Co-Authors

Doug Howell, Waterfowl Biologist

North Carolina Wildlife Resources Commission

Wildlife Management Division

Surveys and Research Program

Joe Fuller, Migratory Game Bird Coordinator

North Carolina Wildlife Resources Commission

Wildlife Management Division

Surveys and Research Program

Roald Stander, M.S. Student

University of Manitoba

Department of Environment and Geography

Master of Environment Program

Special Thanks! – You are viewing this document because you have played an integral role in insuring

this project’s successful fruition. Whether you are a property owner, research advisor, local wildlife

professional, project sponsor, or simply a helping hand, your help does not go unnoticed. I would like

to thank every person involved.

- Daniel Lawson

Graduate Research Assistant

Lawson 1

Background

The American black duck (Anas rupripes) population has been in decline since the 1950s. According to United States Fish and Wildlife Service (USFWS) mid-winter survey estimates, black duck numbers decreased more than 50% from the 1950s to the 1990s (Figure 1) (USFWS 2017). Since this time, the black duck population has stabilized in the Atlantic Flyway (Figure 2).

Figure 2: USFWS Mid-winter Waterfowl Survey Estimates for the American Black Duck in the Atlantic Flyway (1990-2015)

There are several potential explanations for

this decline, including loss in the quantity and

quality of breeding and wintering habitats,

overharvest, and interactions (competition,

hybridization) with mallards (Anas

platyrhynchos) during the breeding and

wintering periods (Anderson et al. 1987, Conroy

et al. 2002). The historical loss of coastal

wetlands in the Mid-Atlantic region has been

significant (Dahl 1990) and their continued

degradation (Tiner 1987, Dahl 2000, Dahl 2006,

Stedman and Dahl 2008, Dahl and Stedman

2013) may limit the ability of this area to support

black duck populations at conservation goals

(Morton et al. 1998, NAWMP 2014).

Although there have been ongoing efforts to

understand the limiting factors of Mid-Atlantic

black ducks during the nonbreeding season

(Cramer et al. 2012, Livolsi 2015, Ringelman et al.

2015), there is a need to better understand the

breeding season limiting factors as well,

especially in light of analyses that suggest long-

term declines in recruitment (Brook 2006).

Consequently, the Black Duck Joint Venture has

determined that there is a need to quantify

regional differences and factors influencing

black duck productivity.

Black ducks breed in highest concentrations in

the eastern Canadian provinces (Rusch et al.

1989), and nesting studies in this region

generally have found nest success is adequate to

maintain the population and is similar to

sympatric mallards (Petrie et al. 2000). A smaller

population of black ducks nest in the Mid-

Atlantic region, however less is known about

their nest success. Until recently, the status of

the breeding black duck population in North

Carolina was poorly understood. North Carolina

represents the southern extent of the species’

breeding range (Stewart 1958, Parnell & Quay

1962, Bellrose 1980). Although breeding black

ducks in North Carolina are well documented,

their long-term population trend and nesting

success is unknown. We suspect that breeding

populations have declined over time, similar to

breeding populations farther north in Virginia

and Maryland (Costanzo and Hindman 2007),

Figure 1: USFWS Mid-winter Waterfowl Survey Estimates for the American Black duck in the Atlantic and Mississippi Flyways (1955-2015)

Mid-winter Survey for American Black Ducks (1955-2015)

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but there is no empirical or baseline data to

support this.

There have been a few past attempts to

quantify the status of breeding black ducks in

North Carolina; however, these were spatially

limited. Parnell and Quay (1962) reported black

duck production between 1938-1958 on Pea

Island, North Carolina and conducted more

thorough nest searching and nest success

research in 1959-1960. They found black duck

nesting was beginning to decline and noticed

lower apparent nest success (69%) than those

observed in the Chesapeake Bay (91%) or

Canada (81%) (Stotts 1956, Wright 1954).

Additional research in 1990 (Fleming et al. 2000)

on Piney Island, North Carolina located 12 nests

with an apparent nest success of only 67%. In

2013, the North Carolina Wildlife Resources

Commission (NCWRC) initiated an aerial black

duck population survey to better understand the

distribution and density of breeding black ducks

in suitable coastal marsh habitat in North

Carolina (NCWRC unpublished data). This survey

is based upon the Atlantic Flyway Breeding

Waterfowl Plot Survey (AFPS; Heusmann and

Sauer 2000). During 2013-2016, the

methodology and survey area was refined to

produce more precise breeding population

estimates. In 2016, the sampling frame

contained 1,267 1-km² plots containing between

5-40% marsh habitat, and 595 plots containing

>40% marsh habitat which was deemed suitable

for nesting black ducks. Of these plots, a

randomly sampled subset of 134 plots was

surveyed via helicopter. Extrapolating the results

of the survey of this subset of plots to the

entirety of North Carolina coastal marsh habitat,

results in an estimate of 2,404 (90% CI = 1,131-

3,678) total black ducks and 694 (90% CI = 500-

888) nesting pairs. However, there is no

knowledge about their nest success and the

factors that could influence those values.

Proposed Research

As per research objective request from the

Black Duck Joint Venture, NCWRC along with the

University of Delaware Department of

Entomology and Wildlife Ecology (UDel) initiated

a project that would quantify the breeding effort

of the American black duck in coastal North

Carolina. Specifically, it is our (NCWRC and UDel)

goal to estimate reproductive parameters of

breeding black ducks in coastal habitat in North

Carolina as a function of nesting habitat quality,

human disturbance, predation, flooding, and

marsh burning.

Breeding Black Duck Survey 2017

Introduction: The North Carolina Wildlife

Resources Commission Breeding Black Duck

Survey conducted in 2017 is built upon surveys

conducted each year since 2013. Since the pilot

survey in 2013, NCWRC has developed a method

to index the breeding black duck population in

suitable coastal marsh habitat in North Carolina.

Results: This year 131 of 135 randomly chosen

1-km² plots were surveyed in three days, April 9-

11, 2017. Three were not surveyed due to

restricted airspace at the Dare County Bombing

Range and one plot could not be surveyed due to

residential development. The survey team

counted 158 total black ducks. Per Atlantic

Flyway Plot Survey (AFPS) protocols, this

represented 75 indicated pairs (IP) (Table 1).

Table 1: Group Size of Observed Black Ducks, April 2017.

Group Size Number of Observations 1 29

2 36

3 3

≥4 3

Mean counts of indicated pairs (IP's) of black

ducks were highest in plots containing >40%

marsh. However, plots containing 5-40% marsh

contributed 44% of the total IP estimate due to

the large number of plots in this survey stratum.

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The total population estimate included 1,048 IP's

and 2,270 total indicated birds (TIB) (Table 2).

Table 2: Population estimates of black ducks by survey strata in coastal North Carolina, April 2017.

Discussion: This survey represents the 5th year

of a multi-year effort to develop an aerial survey

to estimate the size of the breeding black duck

population in suitable coastal marsh habitat in

North Carolina. Since no changes were made to

the survey design in 2017, only results from 2016

and 2017 surveys are directly comparable.

Although the estimate of IP's increased

considerably from 2016, the 90% confidence

intervals overlap, suggesting that increases may

in part be related to sampling error.

Interestingly, TIB's in 2017 was very similar to

2016. Total indicated birds is influenced by

observations of grouped black ducks (>4

observed). Grouped black ducks may represent

migrant black ducks that have not left the state

or local, nonbreeding birds (during the survey

window). Previous modifications to survey

design have been made with the goal of reducing

standard errors of survey estimates. Due to

three plots having an outlier number of IP's

observed, standard error increased considerably

from 2016 (SE=110) to 2017 (SE=205). Moving

forward, there is likely no way around this issue

apart from adding additional survey plots.

The inability to determine the sex of any

observed black ducks from the air introduces

some bias into the estimate of IP’s and TIB’s. Per

AFPS protocols, a conservative approach was

used when recording groups of black ducks of

unknown sex. The inability to distinguish the sex

of black ducks has the potential to influence IP

estimates, both positively and negatively. For

example, groups of three black ducks were

treated as two IP’s. If these three black ducks

were identified as three drakes, they would have

been treated as three IP’s. Alternatively,

observations of single black ducks were counted

as one IP. However, some portion of the single

black ducks observed were likely hens disturbed

from their nest. In 2017, the survey team was

able to positively identify one hen flushing from

a nest and did not include this observation as an

IP.

NC American Black Duck Nesting Study

Introduction: The North Carolina Wildlife

Resources Commission and the UDel coordinate

the American black duck breeding ecology study.

This year we conducted nest searches for

incubating black ducks on six 100 m2 study sites

in coastal North Carolina. We monitored these

nests at seven-day intervals until they were

terminated (hatched, depredated, flooded, etc.).

Vegetation measurements were then taken at

nest termination. A select number of nests were

additionally monitored via trail camera in hopes

to better record causes of nest failure and to

synthesize an incubation break chronology for

black ducks in the southern Atlantic Flyway.

Further, we collaborated with Delta Waterfowl

Foundation to test the efficacy of nest searching

with aerial drones employing thermal imaging

cameras.

Stratum No. of Plots Surveyed

Total No. of Plots

Total Indicated Pairs/ Plot

Estimated Indicated Pairs

Estimated Total Indicated Birds

Plots with >40% Marsh 44 595 0.98 581 (293-870) 1,163 (586-1,740)

Plots with 5%-40% Marsh 88 1,267 0.37 466 (251-681) 1,107 (574-1,639)

Total Survey Area 131 1,862 - 1,048 (706-1,389) 2,270 (1,520-3,019)

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Nest Searching: Although there have been a few

previous attempts to quantify the breeding

status of black ducks in coastal North Carolina

(Parnell & Quay 1962, Fleming et al. 2000), there

were not any datasets available that identified

optimal black duck nesting habitat in this region.

To determine how and where to search for these

nests, we drew from studies conducted farther

north, in the Chesapeake Bay region (Krementz

1991, Costanzo and Hindman 2007, Haramis

1996, Stotts and Davis 1960). Based on our

findings, we decided to focus on three habitat

types: upland buffers (upland habitat that

borders wetlands), islands, and tidal brackish

marsh. Further, we chose six focal areas that

contained these habitats and, per the NCWRC

breeding black duck surveys, breeding black

duck pairs. For the sake of logistics, we placed

four sites northeast of the Pamlico River mouth

along the inner banks of the Pamlico Sound

stretching to the intersection of US 64 and the

Croatan Sound (Figure 3). We placed two study

sites encompassing parts of Pea Island and

Roanoke Island on the Outer Banks of North

Carolina (Figure 4).

Figure 3: Inner Banks Study Sites. Hyde and Dare Counties, North Carolina

Figure 4: Outer Banks Study Sites. Dare County, North Carolina

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Our nest searching technique was modified

from all-terrain vehicle (atv) chain drags used for

locating upland nesting waterfowl (Klett et. al.

1986), where a chain suspended between two

atvs is pulled across standing vegetation. The

chain covers all vegetation in between the atvs

and chain links rattle to produce a metallic sound

that causes nesting hens to flush as the atvs

progress forward. Since our study sites were not

accessible to atvs, we decided to modify the

dragging apparatus so it could be used by two

technicians on foot. Nylon rope seemed to be

the most sensible alternative. We used 100 ft.

lengths of rope and attached aluminum cans

spaced at ~2m intervals along the entire length

of the rope. Every can received small (~3-4 cm)

rocks to serve as noisemakers in lieu of shifting

chain links. Two technicians conducted nest

drags. One technician would stretch the rope to

the edge of a wetland, typically on the edge of a

body of water. The other technician would

stretch the other end of the rope directly inland

from the wetland edge. Once the rope was

extended, both technicians traveled forward

while remaining parallel to one another and the

wetland edge (Figure 5). An additional technician

was used as a spotter that constantly watched

the dragline to identify flushing hens. The

spotter would identify the exact location of the

flushing hen and guide the other technicians to

the nest. Technicians continued forward until a

hen was flushed. Once a hen was flushed, one

technician would approach the nest and begin

data collection while the other stayed at least 5

meters away and recorded data. In areas where

we could not drag the rope due to vegetation

height and rigidity, technicians distanced

themselves 5–25m apart and walked transects of

the selected area. We utilized this technique

specifically on spoil islands in the Pea and

Roanoke Island study sites (Figure 4).

Figure 5: Nest Dragging in North Carolina Brackish Marsh

We initiated nest searching on April 1ST and

continued until June 17th. During that time we

found our nest dragging technique to be a great

success and almost necessary to find the

sparsely positioned black duck nests in the many

thousands of acres of coastal salt marsh that

were surveyed. This season we found and

monitored a total of 56 duck nests. The majority

of nests were black duck (n=47, 84%). Mallard

and gadwall (Mareca strepera) made up the

remaining nests at 4 (7%) and 5 (9%),

respectively (Figure 6).

Figure 6: 2017 Nests Species Composition

The inner banks study areas (Figure 3)

contained mostly brackish marsh and upland

buffer habitat. We found 55% (n=31) of the

nests in these areas. The remaining 45% of nests

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(n=25) came from the island habitats of the

outer banks.

American black ducks favored nesting on the

slightly elevated beach ridges of the inner banks’

brackish marsh. Beach ridges were slightly

higher than the adjacent low marsh because of

sand deposition due to years of wave action.

These ridges were directly adjacent to the open

water of back bays and points jutting into the

sound. The dominant plant species on the

brackish marsh beach ridges (high marsh) were:

black needlerush (Juncus roemerianus), salt-

marsh cord grass (Spartina alterniflora), salt-

meadow cord grass (Spartina patens), and

saltgrass (Distichlis spicata). These species made

up the high marsh, with each species dominating

in patches or zones to form a mosaic vegetation

pattern (Figures 7 - 8).

Figure 7: Brackish High Marsh Mosaic

Figure 8: High Marsh Dominated by Spartina patens

On our two Outer Banks study sites (Roanoke

Island and Pea Island) we spent a great majority

of our time searching natural and man-made

islands within the Pamlico Sound. These islands

proved to be very diverse in topography,

vegetation structure and composition, and black

duck nesting productivity. Topography reflected

how the island was formed, whereas vegetation

structure and productivity reflected how long

ago. Man-made (dredge islands) where typically

elevated and contained an array of plant

communities (Figures 9 - 10). Some of which

were: dune grasslands, maritime shrublands,

upper and lower beach, and maritime vine

tangles. Typically, the older the island, the later

the successional stage. Naturally formed islands

were low lying and were broadly classified as

brackish marsh. As mentioned earlier, each

island had unique black duck nesting

productivity. Most of the variability was

attributed to predator influence and vegetation

structure.

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Figure 9: Man-made Dredge Island > 10 Years Old

Figure 10: Man-made Dredge Island < 10 Years Old

Collectively, nests were located an average of

25.6 meters from open water. Nests located in

flood prone spots, brackish marsh especially,

were slightly elevated (15-30 cm) structures that

consisted of needlerush or Spartina spp. leaves

(Figure 11) and resembled overwater-nesting

diving duck nests. Nests in the brackish marsh

that were not elevated, were tucked deep into

surrounding cover (Spartina patens, Distichlis

spicata, and Juncus roemerianus) and the bowl

was low in profile and mainly constructed of

Spartina patens (Figure 12). Both varieties had

down lining the nest bowl, but a profuse lining

seemed to be less common in elevated

structures.

Figure 11: Elevated Black Duck Nest in Brackish Marsh

Figure 12: Low-Profile Black Duck Nest in Brackish Marsh

On islands in the Outer Banks study sites, black

duck nests were located within dense vegetation

in any combination of warm season grasses,

Rubus, and forbs (Figures 13 - 14).

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Figure 13: Black Duck Nest in Pioneer Island Vegetation

Figure 14: Black Duck Nest in Dense Island Vegetation

We took vegetation measurements at nest

sites once nests were fated (e.g. abandoned,

depredated, etc.). We hoped to get an idea of

the exact microhabitat black ducks chose for

nesting in North Carolina. To achieve this,

technicians collected percent composition with a

Daubenmire frame and Visual Obstruction

Readings (VOR’s) with a Robel pole (Robel et al.

1970). Along with the VOR’s, we recorded

maximum average vegetation height. We found

percent composition at the microhabitat scale to

be; 65% grass, 14% litter, 7% forbs, 5% woody

vegetation, 5% water, and 4% bare soil. Our

average VOR was 0.5 meters meaning there was

more than 50% visual coverage by vegetation

below that height. Finally, max average

vegetation height yielded 0.9 meters.

Earliest and latest nesting initiation, peak(s) of

nesting initiation, and nesting season duration

are questions that have never been confidently

answered of black ducks nesting in coastal North

Carolina. Foremost, we estimated nesting

initiation questions by backdating to the

initiation date (the day the first egg was laid).

We did this by adding the number of eggs in the

nest to the incubation stage in days, and then

took the sum and subtracted it from the date we

discovered the nest. Nesting season was simply

the date the first nest of the season was initiated

until the final nest was terminated. The earliest

date we found black ducks initiating nests was

March 3; the latest date was May 24 (Figure 15).

This year we noticed two separate nest initiation

peaks. The first was during the first two weeks of

April (4/2 - 4/15). The second peak was over the

first two weeks of May (4/30 – 5/13). One

possible explanation for the separate peaks is an

inclement weather event that occurred in mid-

late April. During this time, several flood events

caused a high rate of nest failure in brackish

marsh adjacent to the Pamlico Sound. A few of

our monitored nests remained under water for

an extended period of time. It is possible that

the peak at the beginning of May could have

been a renesting effort.

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Figure 15: 2017 Black Duck Nest Initiation Chronology

Nest Monitoring: This season we monitored 47 black duck nests at 7-10 day intervals (Klett et al. 1986). The product of our monitoring efforts allowed us to have several exposure days to insure that our incubation stage estimates were accurate. Multiple visits also insured more precise nest fates, because it reduced the time terminated nests were exposed to the elements. The composition of nest fates for the 2017 season are as follows in (Table 3).

Table 3: 2017 Nest Fate Composition

We identified hatched nests according to (Klett

et al. 1986). In the nest, we looked for presence

of detached shell membranes and yellowish

feather sheaths or small egg fragments without

membranes in nest material, or presence of

ducklings in the nest bowl. Identifying

abandoned nests was a little bit trickier. On

initial nest visits, we noted the hen status as it

related to the nest (i.e. hen present, eggs warm

and covered, eggs cold and uncovered, etc.).

Along with collecting this data, we covered the

nest with down and other present nest bowl

materials and then made a distinct “X” on top

with two pieces of contrasting vegetation.

Likewise, we used the progression of embryo

development to determine if the hen was still

actively incubating the nest. There were several

factors we identified that caused hens to

abandon nests. (Figure 16).

Figure 16: 2017 Nest Abandonment Causes

The factor that attributed most to nest

abandonment was unfortunately, our own initial

Fate Black Duck Nests

Hatch 9

Abandoned 21

Depredated 12

Nonviable 3

Unknown 2

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activity at the nest site. Of this percentage, all

nests were still in lay or very early in incubation

(< 7days). Of the twelve depredated nests, we

identified several nest predators. Nest predators

identified included American and fish crow

(Corvus brachyrhynchos and Corvus ossifragus,

respectively), bald eagle (Haliaeetus

leucocephalus), raccoon (Procyon lotor),

American mink (Neovison vison), and red

imported fire ant (Solenopsis invicta). Nonviable

nests were nests where all eggs addled before

any other fate. To aid in fating nests, we placed

trail cameras on 35 black duck nests.

Trail Cameras: Placing trail cameras on nests

helped us to understand the nesting ecology of

the black duck in North Carolina. By formatting

cameras to capture images every minute, we

were able to record the frequency and duration

of incubation breaks. Cameras captured many

events that had an impact on the nest fate.

Some of these events included: flooding,

depredation, prolonged incubation breaks, and

abandonment. Sample trail camera photos are

pictured in (Figures 17-20).

Figure 17: April 25 Flooding Event with Submerged Black Duck Nest Pictured in Top-center

Figure 18: Black Duck Hen Elevating Nest Bowl Prior to High-water Event

Figure 19: Bald Eagle Depredation

Figure 20: Raccoon Depredation

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Collaborative Drone Research

Figure 21: Delta Waterfowl Research Drone

Introduction: This year we had the opportunity

to collaborate with Delta Waterfowl Foundation

and the University of Manitoba on research

testing the efficacy of thermal-imagery equipped

drones in avian nest searching. Due to the

sparseness of black duck nests within the

brackish marsh of coastal North Carolina, we saw

this as an opportunity to increase our nest

searching capacity while contributing to drone-

based wildlife sampling research. Roald Stander,

the drone research graduate student with

University of Manitoba, brought his research to

our study sites May 24-30.

Results: We chose study plots 10 – 40 acres in

size that contained known active black duck

nests. We surveyed sites between midnight and

sunrise. Detectability of the thermal targets by

the thermal camera varied from site to site; on

the same site over multiple days; or even on the

same site during a single survey. Different

habitats had certain physical characteristics

which increased/decreased the likelihood of

detecting the targets. Certain meteorological

conditions seemed to greatly influence

detectability. Humidity ultimately negatively

influenced detectability. Thermal reflectance

from moonlight was also observed.

Our goal was to fly three successional missions

over different nights recording coordinates of

each target. The aim of flying multiple times

over the same area was to rule out transient

birds, in that targets observed three nights in a

row would be indicative a nesting bird. Flying

three nights was not achieved at all sites due to

inclement weather. All of the sites that we

visited had a relatively low number of known

nests.

The thermal camera does not detect heat

signatures, but rather detects relative

temperature differences. When the habitat

being surveyed is of a homogenous

temperature, detectability is very high. The

avian thermal targets are the hottest objects

within the field of view (FOV) of the camera and

typically show up clearly.

Discussion: Surveying coastal regions provides

unique challenges due to the humid

conditions. Black ducks in the region typically

select salt marsh hay grass (Spartina patens) as

nesting cover. The structure of the grass seems

to inherently hold moisture due to the c-shaped

structure of the blade. The high levels of low-

lying humidity seems to be exacerbated by the

fact that this is a tidal area.

Despite all the challenges, we located 2/2

known black duck nests and 14 Clapper rail

nests. The known nests were relatively open

from above, and the rail nests were located in

black needlerush. One of the two active black

duck nests included in the survey was extremely

visible from 150 meters (Figure 22) using a

transect-based survey method. We were able to

hover over the nest at a relatively low height, <5

meters, without causing the hen to flush (Figure

24).

We noticed a raccoon momentarily disappear

as it was moving through matted patches of

vegetation, including Spartina patens. This

prompted us to test the detectability of a hot

thermal target (>60⁰C) placed in typical nesting

cover. The thermal camera could only detect

the target at 7’ AGL.

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The habitat inherently had challenges

associated with working in tidal areas. The

observed detectability warrants further testing.

Although we found all known nests, the results

were inconclusive.

Figure 22: Nesting Black Duck Thermal Imaging Snapshot

from 150 meters

Figure 23: Nesting Black Duck Thermal Imaging Snapshot

from 50 meters

Figure 23: Nesting Black Duck Thermal Imaging Snapshot

from <5 meters

Lawson 13

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