Ruffed Grouse Final Paper
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Transcript of Ruffed Grouse Final Paper
21 April 2015Charles McColeB.S. Wildlife and Fisheries SciencesPennsylvania State UniversityUniversity Park, PA, USAEmail: [email protected]
RH: McCole et al. Ruffed Grouse Populations in Scotia Barrens
Proposed Reversal of the Steady Decline in Ruffed Grouse Populations in the Scotia
Barrens Region of Pennsylvania
CHARLES MCCOLE¹, Department of Ecosystem Science and Management, Pennsylvania State
University, 416 Forest Resources Building, University Park, PA, USA
MARK CHRONISTER², Department of Ecosystem Science and Management, Pennsylvania
State University, 416 Forest Resources Building, University Park, PA, USA
SHARA HERMAN³, Department of Ecosystem Science and Management, Pennsylvania State
University, 416 Forest Resources Building, University Park, PA, USA
Corresponding author: [email protected]
Present address: 416 Forest Resources Building, University Park, PA, USA
ABSTRACT
Ruffed grouse (Bonasa umbellus) are a species of concern for the state of Pennsylvania.
Historical records compared to current population densities are revealing a sharp decline across
the state at a rate of ~15% per year. Conservation efforts are needed to reverse the trend enabling
the reestablishment of growing populations across the state. The Centre County population
located on Pennsylvania Game Land #176, commonly called Scotia Barrens, is the basis for our
study. We used an age-structured Leslie matrix model for our population projections. Models
were ran which simulate the management actions that were considered: do nothing, increase
suitable grouse habitat, and implement an open season on avian predators. Population data was
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obtained from a previous long-term study done in the Scotia Barrens form 1976 to 1998 (Storm
2003). Data for the effects of habitat management and avian predator reduction on ruffed grouse
populations was also obtained from the study. The current growth rate (λ) of the grouse
population that we studied is 0.84, which indicates a declining population. Our goal for the study
was to determine if implementing the proposed management action could increase the λ-value
greater than 1.0. After running the models, it was determined that our habitat management action
would increase the λ by 0.19, which would result in a λ of 1.03. We also ran a model for our
management action of reducing the avian predator population by opening a hunting season,
removing a quarter of the predators. Our results showed that λ only increased by 0.05, up to 0.89,
much lower than our target value. Although it is commonly known that ruffed grouse
populations operate in a 10 year cycle, it is clear from our results that habitat plays a very large
role in their success and managing habitat has the greatest effect on their numbers.
Key Words: Ruffed Grouse, Bonasa Umbellus, Scotia, Habitat, Avian, Predation
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The Ruffed grouse (Bonasa umbellus) is the state bird of Pennsylvania. It has become a
commonly hunted game species throughout the state. Ruffed grouse have a maximum lifespan in
the wild of about 8 years. The females mate every year and on average lay 10 eggs per season.
However, 63% of the first nesting events are unsuccessful, meaning that no eggs are hatched
from the nest. In those cases, there is a 100% re-nesting rate, although only 33% of second nests
are successful. Grouse chicks are precocial and will begin to walk on their own and forage upon
hatching. In a week they are able to fly. Grouse mature at age 1 and have a constant fecundity
rate once maturity is reached. Male grouse are territorial although grouse are not monogamous
and both males and females can mate with multiple grouse. They thrive in early successional
habitat which is growing scarce throughout the state of Pennsylvania, resulting in their declining
numbers (Rusch 2000).
Pennsylvania’s population of grouse is rapidly decreasing and if current rates of decline
continue the population will be essentially extinct in 35 years. Specifically, in Scotia Barrens,
abundance has declined 10-15% per year. Though the trend is thought to be primarily a result
from habitat destruction, predation may also be a cause for concern. To reverse the decline of
grouse, habitat must be analyzed to determine if a change in the landscape will contribute to the
reversal in population trajectories (Storm 2003.).
The objective of our study is to increase the current rate of population growth (λ) by a
minimum 0.19, thereby increasing it to 1.03 and promote population increase. Current research
indicated that grouse populations in PA are declining at a rate of 16% a year (λ=0.84). (Table 2,
3). To determine the success at meeting this objective, we looked at population abundance using
flush counts and nest counts. Counting nests can give you the female population abundance as
well as nest productivity numbers. Three actions were chosen and modeled to determine which
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management practices would help us to achieve our objective. They are: do nothing, increase
suitable grouse habitat, and implement an open season on avian predators.
MANAGEMENT ACTIONS
The first action that we are proposing is to do nothing. This is the easiest and most cost efficient
action, as no extra effort will have to be made. For this action, no changes will be made to any of
the current management plans concerning ruffed grouse and the populations will continue to be
observed until quasi-extinction is reached.
Our second action is to increase the suitable habitat of the ruffed grouse in the study area
by at least 50%. Suitable habitat is thought to be one of the biggest contributors to survivability
of ruffed grouse. Grouse thrive in a very narrow age class of vegetation which makes it difficult
to maintain suitable habitat for long periods of time. The constant creation of new habitat
involves clear-cutting tracts of land to enable proper vegetation to grow. However, this process
has the potential of being very costly if done over large tracts of land.
Our third action is to remove a specified number of avian predators from the study area.
Avian predators account for 80% of the mortality of ruffed grouse. Northern goshawk, northern
harriers, great horned owl, and barred owls are the top predators of grouse chicks. By reducing
the number of predators in grouse habitat this would allow a higher rate of chicks to survive to
maturity and a breeding age. By having more breeding adults in a population the abundance
should increase dramatically over time.
To meet the objectives, full cooperation is required from all stakeholders that have an
interest in the success of the species. Hunters provide a valuable source of income that aids in all
management objectives implemented. A compromise needs to be made if the decline of a
popular game species is to be averted. Both alternatives can be met with adjustments to the
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regular hunting season and suspension of the birds of prey protection clause covered in the
Migratory Bird Treaty Act. Allowing for the harvest of a species like the Red Tailed Hawk
would provide a substitute to the temporary removal of Grouse as a game species. Additionally,
the action would increase the survival of ruffed grouse by eliminating a direct prey species. This
two-step solution has the ability to remove the additive effects of harvest and predation and
could return the population to lambda levels greater than 1.0.
STUDY AREA
The Pennsylvania Game Commission maintains about 1.5 million acres of land across the state
of Pennsylvania (PGC 2015). This land is open to the public and maintained by funds generated
through license and firearms sales. Many sites are managed and manipulated to research various
species of game animals to better the experience for hunters. Specific to this grouse project State
Game Land (SGL) 176, also named Scotia Barrens, has been managed to improve and better
understand the habits of ruffed grouse. SGL 176 characteristics are mixed hardwoods common
to the Pennsylvania landscape. One major difference to the area is in the name. The barrens of
the area are derived from the abundance of jack, pitch, and white pines growing in the acidic
soils that are found at SGL176. Elevations ranged from 360 m to 450 m. Temperatures in the
area range from -3.4° C to 21.9° C (National Oceanic and Atmospheric Administration 1985).
1,120 ha of land with in SGL 176 (2500ha total) were used to establish a controlled area. This
area has been selectively managed by the PGC since 1975 to establish ideal habitat for ruffed
grouse and other various game species to prosper (Storm 2003).
METHODS
In our original population model, we used population abundance data obtained from a study done
from 1976-1998 at our study site. Survival and fecundity rates were obtained from a grouse
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demography report put out by the USGS as well as a breeding bird survey. An age-based Leslie
matrix was used to estimate population abundance into the future, based on the current
population, fecundity, and survivability numbers. The model showing the original data and
population projection was used as our do nothing model.
In order to change the current population projection two methods of management were
chosen; increasing favorable habitat and decreasing avian predation. The best grouse habitat is a
mosaic of different age structures. They need early successional patches to nest, hide from
predators, and soft mast crops. Mature growth habitat is needed for hard mast that will feed them
through the winter.
In order to achieve this mosaic patchwork the Barrens were put on a clear-cut rotation.
Every 10 years a 1-ha plot will be systematically chosen to be clear-cut and allowed to
regenerate. Any harvestable trees will be sold while undesired trees will be cleared out of pocket.
In particularly dense blocks an understory burn will take place before the cut in order to recycle
nutrients back into the soil and open up the understory for easier navigation. Hard mast
producing trees will be left in place to ensure that the regeneration is of the appropriate species.
Based on the previous Scotia Barrens grouse study, grouse chick survivability increased
proportionally with an increase in suitable grouse habitat, which is reflected in our tables and
graphs (Storm 2003).
In order to decrease avian predation, there will be a reduction of avian predators in our
study area. Over the entire study site, 2500 Ha, we determined that there were about 20 total
individuals representing the four species that we targeted. The removal of 20% of all avian
predators from the study area, a total of about five individuals over the site, is proposed. A
temporary open season on avian predators will be enacted to allow for hunters to harvest the
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allotted amount to achieve our management action. All falcons are protected under the birds of
prey protection clause in the Migratory Bird Treaty Act. We chose 20% because many avian
predators prey on other nuisance species as well. The changes in survivability and population
abundance is shown in our tables and graphs.
RESULTS
Our do nothing model resulted in a grouse population declining at 16% per year, a λ of 0.84. λ
was reached at the 7 year mark. At that rate, the ruffed grouse population at our study site would
go extinct at the 35 year mark.
It was found that when suitable grouse habitat is increased by 50%, first year survival
will increase by at least 50%. This will ensure that the chicks have a higher rate of survival
during the first year which would bolster the upper age classes in the following years. This
practice increased the lambda to 1.03 within 7 years, an increase of 0.19.
The removal of 20% of avian predators was not found to be as successful. At this rate the
lambda only increased to .89, an increase of 0.05. In order to increase this rate by removal alone
many more birds would need to be harvested which is not feasible.
MANAGEMENT IMPLICATIONS
At the current rate, the grouse population in Scotia Barrens of Pennsylvania will be extirpated
within 35 years. Predation accounts for over 80% of all mortality. Avian predators account for
most of the predation deaths. Management action is drastically needed to protect this vital game
species. A couple management practices have been discussed in this paper such as increased
habitat and an open season on avian predators.
Habitat has shown to be one of the most important determining factors in a successful
ruffed grouse population. Habitat provides adequate cover and the proper food source for all age
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classes. The data for our study was taken from a ruffed grouse study done at the Scotia Barrens
in north central Pennsylvania. The study found that increasing suitable grouse habitat by fifty
percent increases first year survival by at least 50%. For our study we manipulated the habitat
cover to increase abundance. The result was that the lambda increased by 0.19. The resulting
lambda was 1.03 which indicates an increasing population. If that data is accurate, this
management practice would solve the current population decline problems. Additionally, it
shows that even more habitat management could result in higher lambda values. This action has
the potential to create more hunting opportunities and increase hunter satisfaction which would
be a secondary benefit.
The second action that was researched was opening up a season on avian predators,
mainly red-tailed hawks, northern harriers, great horned owls, and barred owls. The main goal
was to increase the lambda above 1.0. After the removal of the allotted predators our lambda
only increased by 0.05, from 0.84 to 0.89 which is far below the goal. However, this directive
will extend the time before the population becomes extirpated from the region. An increase in
predator harvest was considered but avian predators play other important roles in the
environment and nearly all would need to be removed to have a dramatic impact on the growth
rate. Overall, this action did not prove to be a viable option for our goals. For one, the likelihood
that a season would be opened is very slim, as all of these species are protected under federal
law. The second reason is that it isn’t feasible to remove the number of individuals that are
required to increase lambda by our desired amount.
It was found that it is possible to increase the growth rate of the ruffed grouse population
in the region and to prevent future extirpation. The most ideal situation is to indirectly affect the
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population by improving desirable habitat. The alterations to the environment have the
possibility of benefitting other game species and increasing overall hunter satisfaction.
REFERENCES
Fearer, Todd M.; Stauffer, Dean F. 2004. Relationship of ruffed grouse Bonasa umbellus to
landscape characteristics in southwest Virginia, USA. Wildlife Biology. 10(2): 81-89.
Hewitt, David G.; Keppie, Daniel M.; Stauffer, Dean F. 2001. Predation effects on forest grouse
recruitment. Wildlife Society Bulletin. 29(1): 16-23.
Rusch, Donald H.; Destefano, Stephen; Reynolds, Michael C.; Lauten, David. 2000. Ruffed
grouse--Bonasa umbellus. In: Poole, A.; Gill, F., eds. The birds of North America. No.
515. Philadelphia, PA: Birds of North America. 28 p.
Sauer, J. R., J. E. Hines, J. E. Fallon, K. L. Pardieck, D. J. Ziolkowski, Jr., and W. A. Link. 2014.
The North American Breeding Bird Survey, Results and Analysis 1966 - 2012. Version
02.19.2014 USGS Patuxent Wildlife Research Center, Laurel, MD
Storm, G. L., W. L. Palmer, and D. R. Diefenbach. 2003. Ruffed grouse responses to
management of mixed oak and aspen communities in central Pennsylvania. Grouse
Research Bulletin No. 1, Pennsylvania Game Commission, Harrisburg, Pennsylvania,
USA
National Oceanic and Atmospheric Administration. 1985. Climates of the states. II. Gale
Research Company, Detroit, MI. 1572pp.
PGC, Pennsylvania Game Commission, 2015. Pennsylvania State Game Lands. April 24, 2015.
http://www.portal.state.pa.us/portal/server.pt/community/state_game_lands/11363
(accessed April 24, 2015).
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Table 1. Survival and fecundity, presented in a Leslie matrix, for Ruffed Grouse in the Scotia
Barren region of Pennsylvania adjusted for each of our actions. Survival rates were obtained
from a USGS report on Ruffed Grouse. Fecundity rates and the initial population values were
obtained from USGS Patuxent Wildlife Research Center, Laurel, MD North American Breeding
Bird Survey. Fecundity rates reflect an initial nesting event and a secondary nesting event that
occurs in the case of a failed first nest.
Do Nothing 0 1 2 3 4+
0.4447 2.5997 2.3497 1.8497 1.34970.069 0 0 0 0
0 0.5 0 0 00 0 0.45 0 00 0 0 0.35 0.25
Predator Removal0 1 2 3 4+
0.4447 2.5997 2.3497 1.8497 1.34970.0828 0 0 0 0
0 0.5 0 0 00 0 0.45 0 00 0 0 0.35 0.25
Habitat Increase0 1 2 3 4+
0.4447 2.5997 2.3497 1.8497 1.34970.139 0 0 0 0
0 0.5 0 0 00 0 0.45 0 00 0 0 0.35 0.25
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Table 2. The proportion of the total population that is occupied in each age class at any given
year once the asymptotic lambda is reached. All three management actions are represented in the
table. Asymptotic lambda is reached in the 7th year of our projection.
Proportion of individuals in age class (Do Nothing)
0 1 2 3 4+ YearAsym
Lambda0.853082666 0.069959518 0.041565822 0.02221529 0.013176703 7 0.841399663
Proportion of individuals in age class (Predator Decrease)
0 1 2 3 4+ YearAsym
Lambda0.841194106 0.078858414 0.044637943 0.022729369 0.012580168 7 0.883262454
Proportion of individuals in age class (Habitat Increase)
0 1 2 3 4+ YearAsym
Lambda0.803787567 0.109050549 0.053233548 0.023361108 0.010567228 7 1.024524577
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Figures
Figure 1. Semi-log graph showing the population size projections for all age classes as well as
the total population, predicted 35 years into the future for the do nothing action. Age classes 1
through 4+ reach extinction between years 12 and 23. Age class 0, as well as the total population,
reaches extinction around year 35. The consistent population decline correlates with the
asymptotic lambda, 0.84.
Figure 2. Semi-log graph showing the population size projections for all age classes as well as
the total population, predicted 35 years into the future for the habitat increase action. An
asymptotic lambda of 1.024 is reached at year 7. Populations continue to increase throughout the
35 year projection.
Figure 3. Semi-log graph showing the population size projections for all age classes as well as
the total population, predicted 35 years into the future for the avian predator removal action.
Lambda was 0.89, which pushed extinction back 20 years.
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Figure 1.
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Figure 2.
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Figure 3.
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