Published by Associazione Teriologica Italiana Volume 23 (1): 35–48, 2012

Hystrix, the Italian Journal of Mammalogy

Available online at:

http://www.italian-journal-of-mammalogy.it/article/view/4670/pdf doi:10.4404/hystrix-23.1-4670

Research Article

Surveying wolves without snow: a critical review of the methods used in SpainJuan Carlos Blancoa,∗, Yolanda Cortésa

aProyecto Lobo, CBC. C/ Manuela Malasaña 24, 28004 Madrid, Spain

Keywords:Spainwolfsurveyssimulated howlingpack sizesolitary wolves

Article history:Received: 18 April 2011Accepted: 6 July 2012

AcknowledgementsWe are indebted to John Muddeman for cor-recting the English of the first draft and F.J.García and two anomymous reviewers for theircomments. Francesca Marruco and DamianoG. Preatoni made a careful edition of the ma-nuscript.

Abstract

Wolves (Canis lupus) are difficult to survey, and in most countries, snowis used for identifying the species, counting individuals, recording move-ments and determining social position. However, in the Iberian peninsulaand other southern regions of its gobal range, snow is very scarce in winter,so wolves must be surveyed without snow. In Spain and Portugal, wolvesare surveyed through estimating number of wolf packs in summer by meansof locating litters of pups when they are at rendezvous sites. Packs are con-firmed when pups are observed or respond to simulated howling. We makea critical review of this method, exploring the sources of error when estim-ating number of packs, the constraints of the simulated howling method,the sources of uncertainty caused by variations in effort, in observer exper-ience and in other variables. We stress the difficulty of assessing averagepack size and percentage of wolves not included in packs (pairs and solit-ary wolves), which can exceed 30% of the population. These restrictionsmake this method unaccurate and unable to detect moderate or even largepopulation size variations. At the same time, indices based on abundanceof wolf tracks and scats is hampered by the lack of snow and the problem todistinguish them from those of dogs. We conclude that accepting the limit-ations of these wolf surveys and highlighting the uncertainty of the figuresthey provide is more realistic and will encourage a more prudent approachto wolf management.

When faced with uncertainty about aspecies, the first question administrat-ors and the public ask is “How manyare there?”. This appears to be an en-tirely reasonable inquiry, but is usuallythe wrong question. The crucial ques-tions are: “Is the population increas-ing or decreasing?” and “Which para-meters are responsible for the observedtrend?” (Eberhardt and Knight, 1996).How many grizzlies in Yellowstone?

∗Corresponding authorEmail address: jc.blanco2503@gmail.com (JuanCarlos Blanco)

Introduction

Many bird species, like storks and vultures, areconspicuous, breed in very visible nests andare easy to count. In recent decades, reason-able complete censuses of these species havebeen carried out, and results including numberof breeding pairs, its annual change and otherinformative data such as productivity are reg-ularly published (Birdlife International, 2004).Because of this, many managers and the pub-lic think that wolves (Canis lupus) can be mon-itored in the same way. Nevertheless, wolves,as other large carnivores, are elusive, mainlynocturnal, wonder over long distances, and liveat low densities. As Linnell et al. (1998) havestated, “estimating the density, and monitoring

Hystrix, the Italian Journal of Mammalogy ISSN 0394-1914 20th July 2012© CC© 2012 Associazione Teriologica Italianadoi:10.4404/hystrix-23.1-4670

Hystrix, It. J. Mamm. (2012) 23(1): 35–48

the trend, of large carnivore populations is noteasy – in fact, it must be one of the most dif-ficult tasks that a wildlife biologist or managercan undertake!”.In addition, snow seems to be crutial for sur-

veying wolves. Except when surveys are basedmainly on genetic methods, almost all wolf es-timates are based on estimating the number ofreproductive units (i.e. wolf packs). In NorthAmerica, the most common method to estim-ate wolf populations during the last 30 years hascombined estimates of occupied range, averageterritory, and winter pack size as computed byongoing telemetry studies, with estimates of in-terstitial spaces between packs and the percent-age of lone wolves in the population. Estim-ates of occupied range and pack size are carriedout in winter when snow is present, since thesnow tends to unifymembers of the pack (Fuller,1991), and allows researchers to track and countthem from aircrafts, especially when there is atleast one radio-collared wolf in a pack (Fuller etal., 1992; Mech, 1986; Wydeven et al., 2009).In Europe, in recent years, similar methods

also have been used. For example, in Scand-inavia, the area where research and monitor-ing on wolves has reached the highest level inEurope, a combination of snow tracking andfaecal genotyping has been used to establishnumber of packs, pairs, and solitary wolves(Wabakken et al., 2001). Over the last decade,data provided by radio-collared wolves have ad-ded more information on wolf territory, groupsize, and reproductive success. These para-meters are estimated from combined data of 1)pre- and post- reproduction intensive monitor-ing in snow, 2) movement patterns of adult GPS-collared wolves during the parturition period, 3)summer field-work by trained research person-nel and 4) data on age-specific dispersal (Sandet al., 2008). In Poland, wolf numbers have beenestimated with data from winter snow trackingcollected by services of the state forests and na-tional parks (Jedrzejewski et al., 2002). In theAlps, a mixture of snow tracking and geneticanalysis has been used for the annual monitoringof its population (Marucco et al. 2009; Maruccoet al. 2012, this issue).In all these countries, snow is crucial to es-

timate wolf populations. As has been stated by

Wabakken et al. (2001) in Scandinavia, “snowwas a pre-requisite for identifying species,counting individuals, recording movements anddelimiting territories, determination of sex, anddetermining social position (i.e., distinguishingscent-marking residents from solitary non-resi-dents)”. Even in the small Italian Alpine pop-ulation, where wolf surveys are mainly basedon faecal genotyping, snow is needed to trackwolves and collect their scats (Lucchini et al.,2002; Marucco et al., 2009).Nevertheless, in the southern parts of the glo-

bal wolf range, snow is absent during winter,thus making the population estimates more dif-ficult. In Spain and Portugal, number of wolfpacks are estimated in summer by means of loc-ating the litters of pups when they are at rendez-vous sites (Blanco et al., 1992; Llaneza et al.,2005; Pimenta et al., 2005). The objective ofthis review is tomake a critical description of themethods used to survey wolves in Spain, wheresnow is absent in winter from most of the re-gions. The lessons learned from this review canbe helpful to researchers working in the south-ern regions of the wolf range, where snow isvery scarce in winter. This area includes mostof southern Europe, a large region in southernAsia, and part of the southern Unites States.A principal purpose of this review is to dis-

credit the idea that it is possible to obtain ac-curate wolf numbers using this method. Wewill explore its sources of error and levels ofinaccuracy due to: the difficulty in estimatingnumber of packs, the problems of determin-ing average pack size, and the impossibility ofknowing the percentage of wolves living outsidepacks without undertaking intensive radiotrack-ing. Because of these inaccuracies, this methodcan fail to detect large variations in number ofwolves over time. We emphasize the need tohighlight the uncertainty of these wolf surveys,rather than hiding it, is important to carry outwise management of the population.

Spain: a large area to survey in adecentralized country

All the methods to survey wolves must be ad-apted to the geographic and habitat conditions,to the political and social circumstances of the

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Surveying wolves without snow in Spain

area and to resource availability (Linnell et al.,1998). In Spain there is a large wolf popula-tion (few hundred packs), distributed over morethan 100,000 km2 in different habitats, from rel-atively well preserved mountain regions to agri-cultural and densely populated areas. The Span-ish population is contiguous with the Portugueseone (around 63 packs: Pimenta et al. 2005),and both form the large Iberian wolf population(Linnell et al., 2007). In most of these wolf areassnow is completely absent in winter; the groundis covered by snow during a few weeks in winteronly above 1500mof the CantabrianMountains.

Figure 1 – Detected wolf packs in Spain and Portugal. Thefigure shows the river Duero. From Álvares et al. 2005.

Spain is a decentralized country, where wild-life management is under the jurisdiction of eachautonomous region. The Ministry of Environ-ment has the task of coordinating the autonom-ous regions; however, its influence has been re-cently decreasing. There are 17 autonomous re-gions in Spain, and wolves breed in 8 to 9 ofthem. The autonomous regions decide if sur-vey the wolf population, the amounts of fundsinvested, whether to hire scientists for this pur-pose or use their own staff, the interval betweenconsecutive surveys, etc. Most of the Spanishwolves live north of the river Duero, so they areincluded in the Annex V of the Habitats Direct-ive and can be hunted with quotas establishedby the autonomous regions. South of the riverDuero the wolves are protected under the An-nexes II and IV of the Habitats Directive, andcan only be culled under the conditions of art-icle 16 (Fig. 1).Apart from the first wolf survey carried out in

1987 and 1988 (Blanco et al., 1992), no other na-

tional survey has been undertaken. Nowadays,all the surveys are carried out at a regional level.There are big differences in regions characterist-ics and size (from Castilla y León, 94000 km2,to La Rioja, 5000 km2). The wolf populationestimate in Spain is the sum of the most recentsurveys carried out in every autonomous region.

Methods used for wolfsurveys in Spain

The method currently used for wolf surveys hasbeen described and discussed several times in Spain(Blanco, 2008; Blanco and Cortés, 2002; Blanco etal., 1992; Fernández-Gil et al., 2010; Llaneza andBlanco, 2005; Llaneza et al., 2005). The method hastwo parts: a) collecting and analyzing the known in-formation in published and unpublished reports, andb) field work. The ultimate objective of the field workis to find rendezvous sites and confirm pups pres-ence in summer or early autumn to document wolfpacks, assuming that every pack produces just one lit-ter every year.

The field work consists of three main activities:1) Personal (face-to-face) interviews with shepherds,wardens, hunters, biologists, and naturalists, to obtainlocal data on wolf presence: number of wolves seentogether, evidence of breeding (presence of pups, fe-males with visible nipples, dens), wolves killed, dam-age to livestock, and other data. The main object-ive is to detect rendezvous sites or areas of high wolfactivity; 2) Transects travelled on foot or by drivingalong forest roads to detect wolf signs (scats, tracks,scratches, etc.); the assumption is that areas heavilyused and marked with scats in late spring and summercan point to possible locations of dens or rendezvoussite. Special searches of dens and rendezvous sites arethen carried out in areas where many signs have beencollected, and with low human activity, dense veget-ation and water availability (Ausband et al., 2010).3) Confirmation of pup presence mainly from Augustto October during sit-and-wait sessions from vantagepoints and transects using elicited howling (Fuller andSampson, 1988; Harrington and Mech, 1982a) to seeor hear pups.

Two types of packs are defined: confirmed andprobable packs. In the first case presence of pups isconfirmed by direct observation, when pups respondto simulated howling or when pup tracks are found inareas of high activity of adult wolves. The packs aregenerally considered as probable when there is evid-ence of stable presence of several wolves in summer– sightings, livestock damage, signs, etc. – at least 8

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Table 1 – Number of packs detected in the Autonomous Regions of Spain and in Portugal.

Region Packs detected Authors Survey yearGalicia 68 Llaneza et al.1 1999-2003Asturias 36 Llaneza et al.1 2004Cantabria 5 Blanco ans Cortés1 1997Basque Country 1 Arberas1 2010Castilla y León 149 Llaneza and Blanco (2005) 2000-2001Castilla - La Mancha 1 Blanco1 2010Andalousia 2 Carrasco1 2010Total Spain 262

Portugal 631 personal communication

km away from the next nearest pack (considering av-erage pack territories of 200 km2: Cortés 2001), butthe presence of pups has not been confirmed.

For example, in the 2000 and 2001 wolf survey inCastilla y León Region (total area: 94000 km2), 9biologists carried out the field work during 557 man-days. During this time, 2778 personal interviews withlocal people were conducted, 7787 km of forest roadswere scouted for wolf signs, and 209 sit-and-wait ses-sions and 879 simulated howling sessions carried out.In addition, data on 11 radio-collared wolves wereused. In total, 149 packs were located, 107 of whichwere considered confirmed and 42 probable over anarea of about 75200 km2 (80% of the region) (Llanezaand Blanco, 2005).

In total, 265 packs have been detected in 8 regionsof Spain over an area of 120000 km2; documentedwith data collected from 1997 (in Cantabria) to 2010(in Asturias). In Portugal, 63 packs (51 of them con-firmed and 12 probable) were documented over 16000km2 in 2003-2004 (Table 1).

Interpreting the survey dataand assessment of thereliability of the method

In order to assess if the described method ofsurveying packs in summer produces plausibleresults, Blanco et al. (1992) compared the res-ults obtained by different regional teams withinSpain, and additionally compared them to thoseof other authors using different methods. Tell-ería and Sáez-Royuela (1989) calculated thewolf population in an 8000 km2 area in Castillay León by using hunting statistics. They re-lated the number of wolves shot (n = 34) with

the number seen (n = 179) during 52 huntingdrives. Applying this percentage to the num-ber of wolves shot in drives during one year overtheir complete study area, they calculated a min-imum density of 2 wolves/100 km2 during thewinter hunting season. Blanco et al. (1992) es-timated a density for the whole Spanish range of1.5-2.0 wolves/100 km2 (1470-2058 wolves in100000 km2). Furthermore, Purroy et al. (1988)using the same method as Tellería and Sáez-Royuela (1989) calculated the number of wolves(17.5) in the Riaño Hunting Reserve (715 km2)in the León mountains during the hunting sea-son. In spite of the small size of their studyarea, the result (2.44 wolves/100 km2) agreeswith those found by Blanco et al. (1992) for thewhole mountain area of León and for the border-ing region of the Asturias province. Hence, as-suming an homogeneous density of wolves overthe area, the agreement of these estimates indic-ate that the results of these surveys are roughlyplausible, but does not give any measure of ac-curacy and precision. In Portugal, the number ofwolves has not been estimated, but the density ofpacks (Tab. 2) is higher than in Spain, despite amore disturbed habitat. In Minnesota, the dens-ity of packs is much higher than those estimatedin the Iberian peninsula (Tab. 2), but in Min-nesota a pack is defined as a group of >1 wolf,while in Spain and Portugal a pack is defined as agroup of wolves with pups (otherwise they can-not be detected by simulated howling). In Spain,the recent estimates focus only on the number ofpacks, whereas number of wolves has not beenestimated. Blanco et al. (1992) estimated 1500-2000 wolves, but some NGOs claim that the fig-ures are much lower. Considering this last es-

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Surveying wolves without snow in Spain

Table 2 – Packs and wolf densities estimated in the Iberian peninsula and in Minnesota.

Region/Year

Packs1

detectedArea(km2)

Packs/1000km2

Numberof

wolves

Wolves/100km2

Method Reference

Spain1987-88

293 100000 2.9 1500-2000

1.5-2.0 Surveys ofpacks2

Blanco et al.1992

Spain2010

262 120000 2.2 Survey ofpacks2

several authors

Portugal2002-03

63 16000 3.9 Survey ofpacks2

Pimenta et al.2005

Agricultural areaof Castilla y León(Spain)2001

6 2000 3 3.0 Radiotelemetry Blanco andCortés 2002

Bragança (Por-tugal)1995

17-20 4900 4 Radiotelemetryand survey of

packs

Moreira et al.1997

Minnesota1988-89

233 53100 4.4 1521 2.9 Mainlyradiotelemetry2

Erb andDonCarlos

2009Minnesota1997-98

385 73920 5.2 2445 3.4 Mainlyradiotelemetry2

Erb andDonCarlos

2009Minnesota2003-04

485 67852 7.1 3020 4.5 Mainlyradiotelemetry2

Erb andDonCarlos

20091 In Spain and Portugal, a pack is a group of wolves with pups. In Minnesota, a pack is group with ≥ 2 wolves.2 Described in the text.

timate (2000 wolves in 120000 km2), the av-erage density of wolves in Spain would be 1.6wolves/100 km2; this figure is plausible for alarge area, is lower than the density estimatedby Tellería and Sáez-Royuela (1989) in Castillay León using a different method (2 wolves/100km2), and is lower than that recorded in radio-tracking studies carried out in Spain and in wolfsurveys in Minnesota (Tab. 2).The results produced by the method used in

Spain and Portugal seem to be plausible. Wolfdensities estimates are similar using differentmethods in the same area, and fit roughly withdensities calculated in areas of similar latitude.Nevertheless, although this method can producegood general information, it has several disad-vantages. The level of precision cannot bemeas-ured in terms of confidence intervals (CI) aroundthe estimate, and the method has small power todetect moderate changes in the wolf population.In theory, the estimate of the total number of

wolves in an area is given by [(A × B) + C],where A is the number of packs, B is the aver-

age pack size (i.e., the average number of wolvesliving in each pack) and C is the percentageof wolves living out of the packs (solitary andpairs). This formula to census a wolf populationis very simple; however, it is extremely difficultto accurately obtain a value for each variable ofthe formula and sometimes impossible. In thefollowing sections, we will explore the uncer-tainties and challenges we face when estimatingeach of these variables in Spain.

Sources of error in estimating thenumber of packs

The main source of error is failing to detectsome packs, mainly in large study areas wherethe search effort is low. Hence, this method ob-viously produces approximate results. In a re-covering population where adjacent packs aresometimes many kilometres apart, it is easy todiscriminate one pack from the nearest one. Butin saturated populations, where the packs arecontiguous and share a portion of their home

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ranges, identifying every packs is an hard task,especially considering that packs are very dy-namic and unstable. In Denali National Park(Alaska) where the human influence is almostnonexistent, Meier et al. (1995) and Mech etal. (1998) have demonstrated that packs areconstantly changing their territory limits anddisintegrating, splitting, and budding. Some-times packs produce multiple litters, and some-times wolves have multiple pack affiliation. Inour experience, even with several radio-colla-red wolves in one pack, sometimes it is diffi-cult to assess where a pack finishes and wherethe next one starts. Hence, in a high wolf dens-ity area, it is necessary to include an extensiveradio-collaring program to unravel the complexsocial system of a wolf population.

Constraints of the simulated howlingmethod

The simulated howling technique has beenwide-ly described by Harrington and Mech (1982a).Crête and Messier (1987) tested this method inthe field for the first time and obtained a replyrate of 3%. They considered that this low rateposes statistical problems of precision and de-mands high levels of fieldwork and concluded:“We are inclined not to recommend this tech-nique. At best it can provide an index of wolfabundance, but requiring a considerable amountof work and expense”.Fuller and Sampson (1988) made an excellent

evaluation of the method in the field. They used6 contiguous packs with radio-collared wolvesin a 1400 km2 area. The surveys were carriedout by the second author, who did not know thewolves’ locations. They concluded that the lo-gistical and statistical constraints probably pre-vent the use of this technique for surveys overlarge areas, where the aim is to monitor popu-lation changes. However, they located 5 of the6 packs living in the study area, confirming thatwolf howling is a good technique to locate wolfpacks on a relatively small study area. Other au-thors have reviewed this method (Ballard et al.,1995; Ciucci and Boitani, 1998, 2000; Kunkel etal., 2005; Linnell et al., 1998), and they agreedthat it demands a lot of work when used in largeareas, but provided that enough effort and man-

power is employed, it can give reasonable min-imum pack numbers.The surveys carried out in Spain produce a

percentage of packs which are probable or un-confirmed (i.e. the presence of pups has notbeen confirmed). While the criteria to consider apack as confirmed is objective (i.e. documentedpresence of pups), the criteria to consider a packas probable have a wide margin of interpreta-tion and subjectivity. In general, the percent-age of probable packs is directly proportionalto the surface of the study area, and inverselyproportional to the effort (person-days/area sur-veyed). For instance, in 2000-2001 survey of theCastilla y León region (wolf area: 75000 km2)the effort was low (0.7 person-days/100 km2,although considering just the best wolf areas,the effort can rise to 1 person-day/100 km2 oreven higher). Nevertheless, in the 2002-2003survey of Portugal (wolf area: 16000 km2), thesurvey effort was 3.5 person-days/100 km2, 5times higher than in the Castilla y León survey.This could have influenced the results of packdensity: 3.9 and 2.0 packs/1000 km2 were de-tected in Portugal and Castilla y León respect-ively (Llaneza and Blanco, 2005; Pimenta et al.,2005). Therefore, with small rates of search ef-fort (field days/area), the opportunities for con-firming all or most of the packs decrease, so itis necessary to be more flexible when applyingthe criteria to consider probable packs. For in-stance, in Portugal 81% of the packs were con-firmed, whereas is Castilla y León just 72%wereconfirmed. Nevertheless, when the survey isdone in smaller area (e.g. Los Picos de EuropaNational Park, 750 km2), the probable packs cat-egory is not used; we documented only con-firmed packs. Therefore, the major constraint toconsider and evaluate is the difference in searcheffort between areas and years, which is depend-ent on funds availability.

The observer experience

Searching for the aggregations of wolf tracksand scats that usually reveal the presence of ren-dezvous sites, and carrying out simulated howl-ing trials at night, demands a lot of experienceand motivation. Hence, the experience of thefield technicians may influence the results of the

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surveys. Several studies have tested the influ-ence of personal skills in the results of wild-life surveys. For instance, in the surveys ofdesert tortoises (Gopherus agassizii) in Cali-fornia, which do not demand particular skills,the previous experience of the observer appar-ently does not affect their ability to find tortoises(Freilich and LaRue, 1998). In contrast, therewere large differences in the ability of profes-sional biologists and volunteers to find mouf-flons (Ovis sp.) during a day census in France(Garel et al., 2005). In large mammal surveys,several studies have shown that most of the para-meters variation is due to differences among ob-servers capability (Kindberg et al., 2009). InSpain, there is a real case showing the strong in-fluence of the observer skills on the results of awolf survey. In the Asturias region (with wolvesliving in a 6000 km2 area), the number of packshas been surveyed annually or every second yearsince the late 1980s. In 1995, two survey teamsworking independently on the same area repor-ted 12 and 17 wolf packs, respectively, show-ing the big difference of the results collected bypeople with different skills (Blanco and Cortés,2002; Llaneza, 1997).

Sources of error in estimating packsizes

Estimating pack sizes (i.e. the average numberof wolves per pack) is a great challenge. Al-though wolves preying on large ungulates haveshown the largest pack size, a few studies con-sistently show a negative relationship betweenpack size and food acquisition per wolf, thusrejecting the hypothesis that the reason wolveslive in packs is to facilitate their predation onlarge prey (Schmidt and Mech, 1997). Theseauthors believe that wolves live in packs primar-ily because adult pairs can then efficiently sharewith their offspring the surplus of the food avail-able. This study explains why wolves feedingon carcasses can live in packs of ten wolves ormore, as happens in the agricultural areas ofSpain (Blanco and Cortés, 2002). In the past, weused data from the literature (e.g. Blanco et al.1992), but nowadays, managers and the publicdemand more accurate data on average pack sizeobtained from data collected in the field. How-

ever, it is very hard to collect accurate data onpack size because members of packs search forfood alone or in small groups, and it is very un-usual to observe all or most of the packmemberstogether (Mech and Boitani, 2003). The mainfactors assembling the members of the pack aresnow and large prey species in winter (Fuller,1991), and the presence of pups during summeraround dens and rendezvous sites (Ausband etal., 2010). However, in Spain, because of thelack of snow, wolves in winter travel alone or insmall groups, just like in summer.

Estimating pack size in summer

In Spain, Barrientos (2000) estimated the min-imum pack size in summer by watching un-collared wolves at rendezvous sites in agricul-tural areas of the Castilla y León region, wherewolves mainly fed on carrion (Cortés, 2001).Barrientos (2000) observed 26 packs with anaverage of 4.73 pups and 3.58 subadult/adultwolves. The main factor affecting pack sizeestimation was the number of times the packswere observed, suggesting that observationsproduced incomplete counts. In packs observedthree or more times (n = 15), 5.47 pups (range 3-10) and 3.86 >1 year old wolves (range 3-6) werecounted, for a total of 9.33 pack members. Inpacks observed once or twice (n = 11), just 3.73pups (range: 3-8) and 3.18 >1 year old wolves(range 2-4) were detected, for a total of 6.91 packmembers.The restrictions posed by dense vegetation,

the mainly nocturnal activity of wolves livingin disturbed areas (Vilà et al., 1995), and thecharacteristics of the rendezvous site attendancepatterns by wolves make it difficult to count allwolves in the pack together. Rendezvous site at-tendance is very variable and unpredictable, ashas been documented by several authors (Bal-lard et al., 1991; Demma and Mech, 2009; Har-rington and Mech, 1982b; Jedrzejewski et al.,2001; Potvin et al., 2004). For this reason, theavailable pack size estimations in summer mustbe considered as minimum numbers.

Estimating pack size in winter

In much of the wolf distribution area, wolf num-bers are estimated in winter because the snow

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cover allows to follow wolf tracks during highlevels of pack cohesion (Marucco et al. 2012,this volume). In addition, the wolf populationsize in winter, when many pups have died, islower than in late spring or summer, just afterthe births. In North America, winter time, whenall or many of the pack members travel andhunt together, facilitate the location and count-ing of wolves from aircraft if there is a radio-collared wolf in the pack (Fuller et al., 1992;Mech, 1986). Fuller (1991) gave some quantit-ative details on the effects of the snow depth onwolf activity and prey selection in Minnesota.When the mean weekly snow depth in GrandRapids was 22 cm, just 49% of the radio-markedpack members were located together; when thesnow depth increased to 44 cm, 81% of theradio-collared wolves in the same pack were to-gether. Fuller (1991) stated that when huntingbecomes more difficult due to shallow snow,pack cohesion may also be reduced. Wolvesusually hunt alone or in smaller groups in sum-mer when prey are dispersed, but increase packcohesion in winter as prey concentrate in winter-ing areas and snow depth increases. When snowis shallow and deer are more dispersed, wolvesspend less time hunting together and revert tomore summer-like hunting behaviour. Huntingin smaller groups, even alone (Mech 1970, p.227), may increase overall encounter and cap-ture rates of deer and thus increase mean percapita food acquisition. However, deep snowprobably encourages individuals to travel to-gether, follow in the tracks of others, and reduceenergetic demands.Conditions of deep snow and concentration

of ungulates in winter ranges rarely happen inSpain. One of the main issues about the size ofthe wolf population in Spain is with the estima-tion of winter pack size. Barrientos and Fernán-dez (2002) stated that the average group size(the number of wolves travelling together) ob-served in winter in agricultural areas was 3.78,and the average group in the Cantabrian Moun-tains (deduced from snow-tracking) was 3.60wolves. Some authors have claimed that all packmembers travel and hunt together in winter inSpain, even with no snow at all. Consequently,they assumed that the size of the groups seentravelling together correspond to the pack size,

so the total number of wolves in winter can becalculated by multiplying the number of packsby 3.60-3.78. Therefore, the total population inSpain would be 937-1188 wolves (Echegaray etal., 2008). This wrong assumption can producea huge underestimation of the wolf populationsize (Blanco, 2008).Llaneza et al. (2009) applied the snow-tra-

cking method to determine winter pack size, andshowed that the members of the packs split ingroups to travel and hunt even in winter. Dur-ing winter 2006-2007, they carried out 9 simul-taneous transects on snow to estimate pack sizefor two packs in Los Ancares natural park (Can-tabrian Mountains in the Galicia region). InDecember 2006, the 11-12 wolves of the firstpack divided into three groups of 4, 2-3 and 5wolves; the 7 members of the second pack weredivided in groups of 4, 1 and 2 wolves. InMarch2007, the first pack of 11 wolves was divided intwo groups of 2 and 9wolves; the second pack of5 wolves, in two groups of 2 and 3 wolves. In-terestingly, the average size of the wolf groupswhich were travelling together was 3.7, but theaverage winter pack size (the mean of Decem-ber and March) was 8.6 wolves. Unfortunately,these more accurate estimates are carried outhigh wolf density areas, and cannot be extrapol-ated to the rest of the wolf range.

Natural and human-induced variation inpack size

One of the problems in obtaining pack size es-timates over the years is that wolf packs arechanging over time, both in pack and territorysizes. Even in protected wolf populations, packsize can change every year. For instance, thesame pack in the High Arctic studied during 8years by Mech (1995, 1997) had 7, 7, 4, 8, 3,3, 2 and 5 adult/subadult wolves from 1986 to1993. Another pack monitored for 8 years inMinnesota had 2, 6, 2, 7, 6, 6, 11 and 6 wolvesin winter from 1973 to 1981 (Mech and Hertel,1983). Considering a larger sample, in DenaliNational Park (Alaska), the average pack sizeof 30 packs monitored during 9 years changedfrom 4.3 to 13.3 wolves/pack as a consequenceof the variation of the prey vulnerability due tochanges in winter severity (Mech et al. 1998, p.

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Surveying wolves without snow in Spain

41). In these three cases, there was no human-caused mortality.In most wolf surveys carried out in Spain,

we assume that if the number of packs remainsstable, then the total wolf population remainsstable too. But the variation inwolf number doesnot always correspond in a variation in numberof packs. For example, in Denali National Parkover a 4 year period with a natural increase infood availability, the wolf numbers increased by2.5x, but the number of packs only increased by1.7x and the pack size increased by 1.5x (Mechet al., 1998). In Yukon, after severe culling, thewolf numbers were reduced to 52% (from 124wolves in 1985 to 65 in 1986), but the num-ber of packs remained stable (18 packs) and thepack size decreased from 6.9 to 3.6 wolves perpack. In the recovery process, between 1986 and1988, the wolf numbers almost doubled (from65 to 112 wolves) but the number of packs in-creased just 10% (from 18 to 20) (Hayes andHarestad, 2000; Hayes et al., 1991). These ex-amples show that the average pack size can suf-fer large variations as a consequence of changesin food availability, hunting pressure, because ofthe natural increase of recently established pop-ulations, or the recovery of the population afterheavy human-caused mortality. These changesmay be very difficult to detect using the tech-niques described above adopted in Spain.

Sources of error in estimatingwolves not included in packs

In addition to the wolves living in packs, an im-portant percentage of the population can live inpairs or be solitary (i.e. dispersers or peripheralwolves). These loners can be considered a bufferfor the population, making it less vulnerable toexploitation as they are adult individuals that canquickly replace breeders when they die (Fulleret al., 2003). In addition, loners are undetect-able without intensive radiotracking, and theyform a shadow part of the population (Rohner,1997), which is almost impossible to estimateusing the population surveys adopted in Spainand Portugal.Fuller et al. (2003), in an extensive review,

concluded that the average percentage of lonersin North American studies was 12% (range: 7–

20%). But in agricultural habitats of the Castillay León region in Spain, during an intensivestudy carried out mainly with radiotracking, wedocumented higher percentages. In total, wefound that the 14 wolves radio-collared during40.6 wolf-years spent 28% of the radio-days liv-ing out of the packs, alone or in pairs (Blan-co and Cortés, 2007). The three wolves radio-collared in the lowwolf density study area, southof the river Duero, were documented as loners(dispersers plus peripheral wolves) for 1.6% ofthe observations (13.3 wolf-years monitoring),and the rest of the time as territorial wolves liv-ing in packs or in pairs. In contrast, the 11wolves radio-collared in the apparently satur-ated population north of the Duero were docu-mented as loners during 33.5% of the observa-tions (27.3 wolf-years monitoring). The reas-ons for the high percentage of loners north ofthe river Duero likely are the semi-permeableriver Duero barrier, which can limit the dispersal(Blanco et al., 2005), the presence of food sur-plus provided by livestock carrion, which delaysdispersal, and the poor vegetation cover, whichmay limit breeding possibilities and formationof new packs(Blanco and Cortés, 2007).

Other survey methods andindices to monitor populationtrends in Spain

In addition to the method described in this art-icle, other survey and monitoring methods havebeen used or can be used in Spain to assess wolfnumbers, but all of them have severe logistical oreconomic constraints. In the 80’s, the absolutedensity of wolves was estimated in some Span-ish areas using hunting statistics (Tellería andSáez-Royuela, 1986, 1989). But the establish-ment of hunting quotas made this method un-suitable. Genetic analyses on faeces has beenused just once in Spain, in the Basque Country,to identify the minimum number of individu-als (n = 16) in a small area between the Bur-gos and Álava provinces (Echegaray and Vilà,2010). The primary disadvantages of geneticsampling over larger areas are: (1) the high cost,

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(2) the significant field effort needed, and (3) thepresence of genotyping errors that require ex-pensive methods to be reduced (Kunkel et al.,2005; Marucco et al., 2011). The cost of DNAanalyses applied over the whole Spanish rangeis the limiting constraint and further research isneeded to assess sampling designs and optim-ization of the method. Accurate estimates ofpopulation size based on CMR genetic meth-ods have high standards in sampling design,which increase the field work required. Thistechnique has only been tested over relativelysmall areas, mainly in the Alps (Lucchini et al.2002; Marucco et al. 2009; Marucco et al. 2012,this volume), where scats have been collectedin winter by snow-tracking wolves. The lack ofsnow in most of the Iberian wolf range increasesthe problems of proper sample collection. Luc-chini et al. (2002) recommended that scats becollected in winter so the samples are better pre-served for analysis. In addition, scats collec-ted in summer, primarily from roads and trails,were largely only from dominant pack members.Marucco et al. (2009, 2011), who collected wolfscats in the Italian Alps in winter following theirtracks in the snow, estimated that they wouldhave missed 27.7% of young wolves if they hadsimply sampled on roads or human trails, andhighlight the requirements of this technique toavoid errors. Echegaray and Vilà (2010), work-ing in the north-eastern border of the Spanishwolf range, could not estimate the wolf popula-tion size because their scat sampling method didnot accomplish the requirements of the rarefac-tion curves.The use of indirect indices can help tomonitor

wolf populations, especially whenwolf numbersare unknown. However, the statistics of attackson livestock can be misleading, since wolf dam-age directly depends on habitat characteristicsand livestock management (Blanco et al., 1992;Swenson and Andrén, 2005). Hunting statisticsare not applicable because of the hunting quotas,which depend on political criteria. Kunkel et al.(2005), in estimating the annual wolf populationtrend in Idaho, recommended using a combin-ation of 3 different index methods to detect a30-40% population change with 80% power atthe 90% CI level: (1) hunter questionnaire, (2)winter track survey, and (3) summer scat sur-

vey. However, the inability to verify authenti-city of reports and resulting unknown bias pre-cludes the use of hunter surveys as a primarymethod (Kunkel et al., 2005). In Spain and Por-tugal, methods 2 and 3 are impracticable be-cause of the lack of snow and the abundance offree-ranging dogs, which makes the recognitionof wolf scats difficult. For instance, Echegarayand Vilà (2010), in the Basque Country, collec-ted faeces preliminarily identified as belongingto wolves, but the subsequent genetic analysesshowed that, of 86 scats, just 31 actually corres-ponded to wolf (53 corresponded to dog and 2to red fox, Vulpes vulpes).Crête and Messier (1987), after assessing in-

dices of wolf density in Quebec, concluded that“there is no inexpensive way to evaluate the ab-solute wolf density over large forested areas”.We come to the same conclusion, but in Spainthe lack of snow makes things worse. In thesame way, Boitani and Ciucci (1993), after re-viewing the wolf population estimates in Italyhave concluded: “The current estimates and tho-se published in the past must be interpreted asorders of magnitude of the populations and theirtrends, rather than as figures able to support stat-istical comparisons”. Themonitoring of the areaoccupied by wolves seems to be the easiest in-dicator of the population trend. An increaseor decrease of the range usually reflects the in-crease or decrease of the population. Neverthe-less, the population can suffer important vari-ations, while distribution area remains stable. Inaddition, an assessment of the combination ofseveral indices, such as livestock attack statist-ics, records of dead wolves, pack surveys in se-lected areas (mainly on the borders of the wolfrange), may give an insight into wolf populationtrends. All the ecological and demographic datathat can be collected in simultaneously carriedon intensive radio-tracking studies, can be help-ful to interpret the information produced by thesurveys.

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Accepting uncertainty and theimpossibility to detect smallvariations

Using the methods described above in Spain andPortugal, and given the scarce information avail-able on pack size and solitary wolves and pairsin different regions and under different circum-stances, it is not possible to obtain an accur-ate figure of wolf numbers. In addition, ac-curate knowledge on the number of packs isvery difficult, and is perhaps restricted to lim-ited areas (national parks or provinces with a fewwolf packs), where it is possible to apply a highsearch effort and obtain detailed knowledge ofthe area. The results of these surveys are likelymore inaccurate as the area’s size, and hence thewolf population, increase. The wolf pack sur-veys are probably far more accurate in areas withexpanding (low density) wolf populations in theborders of the wolf range, where packs are ap-parently well separated; estimates are more dif-ficult in saturated areas where the radiotrackingstudies have shown a large overlap among packhome ranges (Authors, unpublished data), andthe presence of floaters and pairs settled in theinterstices of packs’ territories in some cases ob-scure the pack delimitation. Therefore, at lowwolf population levels (for instance, the SierraMorena population or the Portuguese segmentsouth of the river Duero) monitoring techniqueswill need to intensify. Methods should be usedthat provide greater precision and higher levelsof resolution needed to detect small and immedi-ate changes in population status to avoid popula-tion extinction. At higher population levels (thelarge north-western Iberian population), monit-oring precision and resolution can be relaxed aslarger long-term trends or changes in populationlevels are of more interest (Kunkel et al., 2005).Even if the number of packs does not change,

the variation in the pack size and in the per-centage of floaters can have a huge influence onthe total number of wolves (Blanco and Cortés,2007). Nevertheless, in order to detect theseparameters without snow, intensive ecologicalstudies with radiotracking and/or genetic ana-lyses are needed, and these kinds of studies arevery scarce in Spain. When wolves are hunted

(as is the case in much of Spain north of the riverDuero) the impact of the wolf removal is verydifferent in populations with large packs and alot of floaters ready to replace the missing packmembers, than in populations with small packsand a lack of adult solitary wolves. Using themethod described in this paper for Spain, it isvery difficult to assess wolf population changesderived from changes in food resources or anincrease of wolf hunting. For instance, afterthe outbreak of the Bovine Spongiform Enceph-alopathy (BSE) in Spain in the year 2000, thecarrion pits have been gradually removed fromthe field. In addition, the laws banning leav-ing livestock carcasses in the field, that weretraditionally ignored, are now strictly enforced.Nowadays, the dead livestock is officially col-lected and burned both from the small and thebig farms, and hence, the availability of live-stock carrion in the field has apparently droppedin agricultural and semi-natural areas. Theselivestock carcasses abandoned in the field rep-resented a huge amount of biomass available towolves (Tellería and Sáez-Royuela, 1989), andwere a staple food for wolves in agriculturalareas, forming 75% of their diet biomass beforeBSE (Cortés, 2001).In theory, this food decrease can change the

population parameters resulting in fewer loners,smaller pack sizes and a general reduction inthe wolf population (Blanco and Cortés, 2007).Since we have not updated surveys in muchof the Spanish wolf range (the last survey inCastilla y León region, which holds more than50% of the Spanish wolf population, was car-ried out in 2000 and 2001) and because of thelow power of the surveymethod described aboveto detect small or moderate variations in wolfnumbers, there are no data on wolf trends. Nev-ertheless, for the first time in 40 years, a smallbut clear reduction of the wolf distribution hasbeen recorded, as has been shown in the At-las of the Spanish Mammals published by theMammal Society (SECEM) in 2003 and 2007(Blanco et al., 2002, 2007). The distributionarea reduction is compatible with the theoreticalpopulation changes predicted, but so far it hasbeen impossible to obtain robust data on packsize and the percentages of loners and pairs toconfirm our hypothesis, because of the political

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constraints on wolf research in some parts ofSpain.As happens with other surveys of large car-

nivores, there is a degree of uncertainty sur-rounding surveys in Spain and Portugal. Un-certainty, in this context should not be confusedwith ignorance. As Garshelis (2002) has statedin relation to the situation of several bear spe-cies, “in the interest of both science and con-servation, biologists should emphasize the un-certainties of population assessments and thusthe necessity of more rigorous research”. Nev-ertheless, to acknowledge this uncertainty canbe difficult from a political perspective, because,“inmost human societies, knowledge empowers,whereas uncertainty signifies fallibility, timidityand weakness”. In addition, managers and pub-lic are used to have more accurate figures of birdcensuses and do not accept the uncertainties sur-rounding the wolf surveys. We think that accept-ing the limitations of the wolf surveys and high-lighting the uncertainty of the produced estim-ates is more realistic and will encourage a moreprudent approach to wolf management.

References

Álvares F., Barroso I., Blanco J.C., Correia J., Cortés Y.,Costa G., Llaneza L., Moreira L., Nascimento J., PalaciosV., Petrucci-Fonseca F., Pimenta V., Roque S., Santos, E.,2005. Wolf status and conservation in the Iberian Pen-insula. Panel. Frontiers of Wolf Recovery. Organized byThe InternationalWolf Center andWolf Specialist Group(IUCN). 1-4 October 2005, Colorado Springs, Colorado.

Ausband D.E., Mitchell M.S., Doherty K., Zager P., MackC.M., Holyan J., 2010. Surveying predicted rendezvoussites to monitor gray wolf populations. Journal of Wild-life Management 74: 1043–1049.

Ballard W.B., Ayres L.A., Gardner C.L., Foster J.W., 1991.Den site activity patterns of gray wolves, Canis lupus,in south central Alaska. Canadian Field-Naturalist 105:497–504.

Ballard W.B., McNay M.E., Gardner C.L., Reed D.J., 1995.Use of line-intercept track sampling for estimating wolfdensities. In: Carbyn L.N., Fritts S.H., Seip D.R. (Eds.).Ecology and Conservation of Wolves in a ChangingWorld. Canadian Circumpolar Institute. Occasional Pub-lication No. 35. Edmonton, Alberta. 469–480.

Bárcena F., 1976. Censo de camadas de lobos en la mitadnorte de la provincia de Lugo (año 1975) y algunos da-tos sobre la población de los mismos. Boletín EstaciónCentral Ecología 5: 45–54. [in Spanish]

Barrientos L.M., 2000. Tamaño y composición de diferentesgrupos de lobos en Castilla y León. Galemys (n.e.) 12:249–256. [in Spanish]

Barrientos L.M., Fernández A., 2002. ¿Cómo estimar eltamaño de grupo en las poblaciones ibéricas de lobos?Seminario sobre “Propuestas para el estudio de la dinám-ica de las poblaciones de lobo en la Península Ibérica”.Fuentes de Nava (Palencia). 1 y 2 de Noviembre de 2002.ASCEL. [in Spanish]

Birdlife International, 2004. Birds in Europe: population es-timates, trends and conservation status. Birdlife Conser-vation Status Series nº 12. Birdlife Conservation. Cam-bridge.

Blanco J.C., 2008. ¿Cuántos lobos hay en España? Preci-siones metodológicas. Quercus 267: 80–81. [in Spanish]

Blanco J.C., Cortés Y., 2002. Ecología, censos, percepcióny evolución del lobo en España. Análisis de un conflicto.SECEM, Málaga. [in Spanish]

Blanco J.C., Cortés Y., 2007. Dispersal patterns, mortalityand social structure of wolves living in agricultural hab-itats in Spain. Journal of Zoology 273: 114–124.

Blanco J.C., Cortés Y., Virgós E., 2005. Wolf response totwo kinds of barriers in an agricultural habitat in Spain.Canadian Journal of Zoology 83: 312–323.

Blanco J.C., Cuesta L., Reig S., 1990. El lobo (Canis lupus)en España. Colección Técnica. ICONA. Madrid. 130 pp.[in Spanish]

Blanco J.C., Reig S., Cuesta L., 1992. Distribution, statusand conservation problems of the wolf Canis lupus inSpain. Biological Conservation 60: 73–80.

Blanco J.C., Sáenz de Buruaga M., Llaneza L., 2002. Lobo.Canis lupus Linnaeus, 1758. In: Palomo L.J., Gisbert J.(Eds.). El atlas de los mamíferos terrestres de España.DGCN, SECEM y SECEMU EDS., Málaga. 234–237.[in Spanish]

Blanco J.C., Sáenz de Buruaga M., Llaneza, L., 2007.Canis lupus. In: Palomo L.J., Gisbert, J., Blanco J.C.(Eds.). Atlas y Libro Rojo de los Mamíferos Españoles.SECEM, SECEMU, Ministerio de Medio Ambiente yTragsa. 272–276 [in Spanish]

Boitani L., Ciucci P., 1993. Wolves in Italy: critical issuesfor their conservation. In: Promberger W., Schröder W.,(Eds.). Wolves in Europe: status and perspectives. Mu-nich Wildlife Society, Ettal, Germany. 74–90.

Ciucci P., Boitani L., 1998. Il lupo. Elementi di biolo-gia, gestione, ricerca. Istituto Nazionale per la FaunaSelvatica “Alessandro Ghigi”, Documenti Tecnici, 23. [inItalian]

Ciucci P., Boitani L., 2000. Simulated howling survey ofwolves in the Pollino National Park, Italy. A cost-benefitanalysis. Abstract In: “Beyond 2000. Realities of GlobalWolf Restoration”. Duluth (Minnesota), 23-26 February2000. International Wolf Center & Univ. Minnesota, Du-luth. 83.

Cortés Y., 2001. Ecología y conservación del lobo (Canislupus) en medios agrícolas. Ph. D. dissertation, Univer-sidad Complutense deMadrid, Madrid. 272 pp. [in Span-ish]

Crête M., Messier F., 1987. Evaluation of indices of graywolves, Canis lupus, density in hardwood conifer-forestsin southwestern Quebec. Canadian Field-Naturalist 101:147–152.

Demma D.J., Mech L.D., 2009. Wolf use of summer territ-ory in northeastern Minnesota. Journal of Wildlife Man-agement 73: 380–384.

46

Surveying wolves without snow in Spain

Echegaray J., Vilà C., 2010. Noninvasive monitoring ofwolves at the edge of their distribution and the cost oftheir conservation. Animal Conservation 13: 157–171.

Echegaray J., Leonard J., Vilà C.. 2008. ¿Está asegurada laconservación del lobo ibérico a corto plazo? Quercus236: 14–23. [in Spanish]

Eberhardt L.L., Knight R.R., 1996. How many grizzlies inYellowstone?. Journal of Wildlife Management 60: 416–421.

Erb J., DonCarlos M.W., 2009. An overview of the legal his-tory and population status of wolves in Minnesota. In:Wydeven A.P., Van Deelen T.R., Heske E.J. (Eds.). Re-covery of gray wolves in the Great Lakes region of theUnited Estates. Springer, New York. 49–64.

Fernández-Gil A., Álvares F., Vilà C., Ordiz A. (Eds.) 2010.Los lobos de la península Ibérica, propuestas para el dia-gnóstico de sus poblaciones. ASCEL, Palencia, 208 pp.[in Spanish]

Freilich J.E., LaRue E.L., 1998. Importance of observer ex-perience in finding desert tortoises. Journal of WildlifeManagement 62: 590–596.

Fuller T.K., 1989. Population dynamics of wolves in north-central Minnesota. Wildlife Monographs 105.

Fuller T.K., 1991. Effect of snow depth on wolf activityand prey section in north central Minnesota. CanadianJournal of Zoology 69: 283–287.

Fuller T.K., Murray D.L., 1998. Biological and logistical ex-planations in variations in wolf population density. An-imal Conservation 1: 53–57.

Fuller T.K., Sampson B.A., 1988. Evaluation of a simulatedhowling survey for wolves. Journal of Wildlife Manage-ment 52: 60–63.

Fuller, T.K., and Snow, W.J. 1988. Estimating winter wolfdensity using radiotelemetry data. Wildlife Society Bul-letin 16: 367–370.

Fuller T.K., Berg W.E., Radde G.L., Lenarz M.S., JoselynJ.B., 1992. A history and current estimate of wolves dis-tribution and numbers in Minnesota. Wildlife SocietyBulletin 20: 42–55.

Fuller T.K., Mech L.D., Cochrane J.F., 2003. Wolf pop-ulation dynamics. In: Mech L.D., Boitani L. (Eds.).Wolves: Behavior, Ecology, and Conservation. Univer-sity of Chicago Press, Chicago, Illinois. 161–191.

Garel M., Cugnasse J.-M., Gaillard J.-M., Loison A., San-tosa Y., Maublanc M.-L., 2005. Effect of observer exper-ience on the monitoring of a mouflon population. ActaTheriologica 50: 109–114.

Garshelis D., 2002. Misconceptions, ironies, and uncertain-ties regarding trends in bear populations. Ursus 13: 321–334.

González F., Palomero G., Naves J., Solano S., 1987. Situa-ción del lobo ibérico en Asturias (1986). Pp. 28-29. Ellobo ibérico. II Jornadas Estudio y Debate. Salamanca.[in Spanish]

Harrington F.H., Mech L.D., 1982a. An analysis of howl-ing response parameters useful for wolf pack censusing.Journal of Wildlife Management 46(3): 686–693.

Harrington F.H., Mech L.D., 1982b. Patterns of homesiteattendance in two Minnesota wolf packs. In: HarringtonF.H, Paquet P.C. (Eds.). Wolves of the world. Perspect-ives of behavior, ecology and conservation. Noyes Pub-lications. New Jersey. USA. 81–105.

Hayes R.D., Harestad A.S., 2000. Demography of a recov-ering wolf population in the Yukon. Canadian Journal ofZoology 78: 36–48.

Hayes R.D., Baer A.M., Larsen D.G., 1991. Population dy-namics and prey relationships of an exploited and recov-ering population in the southern Yukon. Yukon Fish andWildlife Branch Final Report. TR-91-1: 1–67.

Jedrzejewski W., Nowak S., Schmidt K., Jedrzejewska B.,2002. The wolf and the lynx in Poland – results of acensus conducted in 2001. Kosmos 51: 491–499. [in Pol-ish with English summary]

Jedrzejewski W., Schmidt K., Theuerkauf J., JedrzejewskaB., Okarma H., 2001. Daily movements and territoryuse by radio-collared wolves (Canis lupus) in BialowiezaPrimeval Forest in Poland. Canadian Journal of Zooogy79: 1993–2004.

Kindberg J., Ericsson G., Swenson J.E., 2009. Monitor-ing rare or elusive large mammals using effort-correctedvoluntary observers. Biological Conservation 142: 159–165.

Kunkel K., MackC.M., MelquistW.E., 2005. An assessmentof current methods for surveying and monitoring wolves.Nez Perce Tribe, Lapwai, Idaho, USA.

Linnell J.D.C., Salvatori V., Boitani L., 2007. Guidelines forpopulation level management plans for large carnivore inEurope. LCIE report prepared for the European Commis-sion.

Linnell J.D.C., Swenson,J.E., Landa A., Kvam T., 1998.Methods for monitoring European large carnivores – Aworldwide review of relevant experience. NINA Opp-dragsmelding 549: 1–38.

Lucchini V., Fabbri E., Marucco F., Ricci S., Boitani L.,Randi E., 2002. Noninvasive molecular tracking of col-onizing wolves (Canis lupus) packs in theWestern ItalianAlps. Molecular Ecology 11: 857–868.

Llaneza L., 1996. Selección de presa y alimentación delLobo Ibérico (Canis lupus L.) en el Parque Natural deSomiedo. Departamento de Biología de Organismos ySistemas. Universidad de Oviedo. [in Spanish]

Llaneza L., 1997. Evolución y situación del lobo enAsturias.In: Palacios B., Llaneza L. (Eds.). I Seminario sobre elLobo en los Picos de Europa. Grupo Lobo y SociedadEspañola para la Conservación y el Estudio de los Mamí-feros (SECEM). Oviedo. 29–42

Llaneza L., Blanco J.C., 2005. Situación del lobo (Canislupus L.) en Castilla y León en 2001. Evolución de suspoblaciones. Galemys (n.e.) 17: 15–18.

Llaneza L., Herrador R., García V.M., Callejo A., 2009.Seguimiento estival e invernal de lobos en los Ancareslucenses. Galemys 21 (número especial) 21: 217–231.[in Spanish]

Llaneza L., Ordiz A., Palacios V., Uzal A., 2005.Monitoringwolf populations using sampling transects and howlingpoints. Wildlife Biology in Practique 1: 108–117.

Marucco F., Pletscher D.H., Boitani L., Schwartz M.K., Pil-grim K.L., Lebreton J.D, 2009. Wolf survival and pop-ulation trend using non-invasive capture-recapture tech-niques in the Western Alps. Journal of Applied Ecology46: 1003–1010.

Marucco F., Boitani L., Pletscher D.H., Schwartz M.K.,2011. Bridging the gaps between non-invasive geneticsampling and population parameter estimation. EuropeanJournal of Wildlife Research 57: 1–13.

47

Hystrix, It. J. Mamm. (2012) 23(1): 35–48

Marucco F., Avanzinelli E., Boitani L., 2012. Non-invasiveIntegrated Sampling Design to Monitor the Wolf Popula-tion in Piemonte, ItalianAlps. Hystrix (online first) 23(1).doi:10.4404/hystrix-23.1-4584.

Mech L.D., 1970. The wolf. The ecology and behaviourof an endangered species. Univesity of Minnesota Press,Minneapolis.

Mech L.D., 1986. Wolf population in the Central SuperiorNational Forest, 1967-1985. Pages 1–6 in USDA ForestService North Central Forest Experiment Station Re-search Paper, NC-270.

Mech L.D., 1995. A ten-year history of the demography andproductivity of an arctic wolf pack. Arctic 48: 329–332.

Mech L.D., 1997. The arctic wolf: ten years with the pack.Voyageur Press, Stillwater, Minnesota.

Mech L.D., Boitani L., 2003.Wolf social ecology. In: Mech,L. D., and L. Boitani (Eds.) 2003. Wolves: Behavior,Ecology, and Conservation. University of Chicago Press.1–34.

Mech L.D., Hertel H.H., 1983. An eight year demography ofa Minnesota wolf pack. Acta Zool. Fenn. 174: 249–250.

Mech L.D., Adams L.G., Meier T.J., Burch J.W., Dale, B.W.,1998. The Wolves of Denali. University of MinnesotaPress. Minneapolis.

Meier T.J., Burch J.W., Mech L.D., Adams L.G., 1995.Pack structure and genetic relatedness among wolf packsin a naturally-regulated population. In: Carbyn L.N.,Fritts S.H., Seip D.R. (Eds.) Ecology and Conservationof Wolves in a Changing World. Canadian CircumpolarInstitute. Occasional Publication No. 35. Edmonton, Al-berta. 293–302.

Moreira L., Rosa J.L., Lourenço J., Barroso I., PimentaV., 1997. Projecto Lobo; Relatorio de Progresso, 1996.(Cofinanciado pela U.E. – Programa Life). Ministériodo Ambiente e dos Recursos Naturais; Instituto de Con-servação da Natureza. Parque Natural de Montesinho,Bragança (Portugal). 61 pp. [in Portuguese]

Pimenta V., Barroso I., Álvares F., Correia J., Ferrao daCosta G., Moreira L., Nascimento J., Petrucci-FonsecaF., Roque S., Santos G., 2005. Situaçao populacionaldo lobo em Portugal: resultados do censo nacional2002/2003. Relatório Técnico. Instituto da Conservaçaoda Natureza/ Grupo Lobo. Lisboa. [in Portuguese]

Potvin M.J., Peterson R.O., Vucetich J.A., 2004. Wolfhomesite attendance patterns. Canadian Journal of Zo-ology 82: 1512–1518.

Purroy F., Clevenger A.P., Costa L., Sáenz de Buruaga M.,1988. El lobo y el oso en Riaño. Quercus 28: 20–24.

Rohner C., 1996. The numerical response of great hornedowls to the snowshoe hare cycle: consequences of non-territorial “floaters” on demography. Journal of AnimalEcology 65: 359–370.

Rohner C., 1997. Non-territorial “floaters” in great hornedowls: space use during a cyclic peak of snowshoe hares.Animal Behavior 53: 901–912.

Sand H., Wabakken P., Zimmerman B., Johansson Ö., Ped-ersen H.C., Liberg O., 2008. Summer kill rates and pred-ation patterns in a wolf-moose system: can we rely onwinter estimates? Oecologia 156: 53–64.

Schmidt P.A., Mech L.D., 1997. Wolf pack size and foodadquisition. American Naturalist 150: 513–517

Swenson J.E., Andrén H., 2005. A tale of two countries:large carnivore depredation and compensation schemesin Sweden and Norway. In: Woodroffe R., Thirgood S.,Rabinowitz A. (Eds.) People and wildlife: conflict or co-existence? Cambridge University Press, London. 323–339.

Tellería J.L., Sáez-Royuela C., 1986. El uso de la frecuen-cia en el estudio de la abundancia de grandes mamí-feros. Acta Oecologica/Oecologia Applicata 7: 69–75.[in Spanish]

Tellería J.L., Sáez-Royuela C., 1989. Ecología de una pobla-ción ibérica de lobos (Canis lupus). Doñana, Acta Ver-tebrata 16: 105–122.

Vilà C., Urios V., Castroviejo J., 1995. Observations on thedaily activity patterns in the Iberian wolf. In: Carby L.N.,Fritts S.H., Seip D.R. (Eds.) Ecology and conservation ofwolves in a changing world. Canadian Circumpolar Insti-tute , Occasional Publication No. 35. 335–340.

Wabakken P., Sand H., Liberg O., Bjärvall A., 2001. The re-covery, distribution, and population dynamics of wolveson the Scandinavian peninsula, 1978-1998. CanadianJournal of Zoology 79: 710–725.

Wydeven A.P., Wiedenhoeft J.E., Schultz R.N., Thiel R.P.,Jurewicz R.L., Kohn B.E., Van Deelen T.R., 2009. His-tory, population growth, and management of wolves inWisconsin. In: Wydeven A.P., Van Deelen T.R., HeskeE.J., (Eds.) Recovery of the grey wolves in the Great lakesregion of the United States. Springer, New York. 87–106.

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