Preliminary Modeling of Bicknell's Thrush Population Growth

PRELIMINARY MODELING OF POPULATON GROWTH OF BICKNELL'S THRUSH ACROSS A LATITUDINAL GRADIENT
Kent McFarland and Chris Rimmer Vermont Center for Ecostudies
Yves Aubry and Sebastien Paradis, Environment Canada, Canadian Wildlife Service
Scott Sillett, Smithsonian Migratory Bird Center

-19.5% annual decline -18.9% annual decline -7% annual decline

Declining annually at a rate of 19.5 % in Nova Scotia H.E.L.P. – Bird Studies Canada

Declining annually at a rate of 18.9 % in New Brunswick H.E.L.P. – Bird Studies Canada

7% Annual Decline 9 Years 17 Routes 7% Annual Decline

Mountain Birdwatch

Demographic Study Sites Gaspe (1998-2003) Stratton Mountain (1997 – 2008) Mount Mansfield (1992-2008)

Study Areas Mt. Mansfield Stratton Mountain

Capture-Mark-Recapture Methods
Active (broadcast elicitation) and passive mist-netting to capture or recapture BITH (late May- early Sept).
Age and sex determined at capture
No. Individuals Captured:

Nest Monitoring Methods
Nests located with telemetry (~80%)
Efficient, minimizes disturbance, less bias
Females outfitted with a small radio transmitter

n=4 n=4 n=10 n=3 n=5 n=7 Overall mean = 2.2 males : female n = number years Breeding Adult Sex Ratios

Nestling Sex Ratios

r r r r r r r r r r 5 Males - 95% KHR 5 Males - 50% KHR Bicknell’s Thrush Kernel Home Range Overlap

Adjacent Female Territories

adapted from R.F. Morris (1951). The effects of flowering on the foliage production and growth of balsam fir. Forestry Chronicle 27: 40-57.

“ Predators (red squirrels) appear to be the principal limiting factor.” George J. Wallace 1939 0/1 nest successful in 1933 4/13 nests successful in 1935

Nest Predation Results
Null model is the most plausible
Year is ranked 2 nd
Distance to ski trails has little support
No apparent edge effects
Predation appears to be random

171 BITH nests monitored
48% successful
75% of failed nests due to predation

Nest-survival module in Program MARK
Global model with 4 groups:
Study mountain (Mansfield or Stratton)
Annual red squirrel presence (high or very low to absent)
Eight years were grouped as high red squirrel years (n=97 nests) and 7 years were grouped as low red squirrel years (n = 77 nests)
Covariates:
Distance to nearest ski trail or work road edge
Stem density 5m radius
Nest height

Nest Survivorship Models

27-day nesting cycle: 19% success in squirrel years 57% in no squirrel years No Squirrels Squirrels

Annual Fecundity (females/female)

Annual Survivorship Estimation Program MARK
Global model contained:
Study mountains (Mansfield, Stratton, Gaspe)
Study areas with abrupt linear edges from ski trails and work roads vs. natural areas
Male, Female and SY, ASY
Possible that SY adults emigrate after their first breeding season while older birds tend to have very high site fidelity, we used transient in our modeling which compares Φ and t in year +1 as one group (transients) and year 2+ as a second group.
p(site*habitat) chosen a priori .

Mark-Recapture Annual Survivorship Models

Estimates of Population Growth Rate
Used a two-stage Leslie matrix model.
Parameterized with estimates of annual survivorship and fecundity.
Survival from fledging until first breeding is unknown. We used 0.3 as an estimate of fledgling survival.
Model calculations performed in MS EXCEL using POPTOOLS add-in module (Hood 2002).

Population Growth Rate

Relative Contributions of Survival and Fecundity to Population Growth Rate

Acknowledgements
We are grateful to the many field biologists and volunteers who dedicated countless hours of field work under conditions that were often difficult.
We also thank the Stratton Mountain Resort, the Mt. Mansfield Company, for valuable logistic support.
VCE’s work on this project through September of 2007 was conducted under the Vermont Institute of Natural Science, to whom we express thanks for its institutional support.
Funding was generously provided by the Conservation and Research Foundation, the Davis Conservation Foundation, the Frank and Brinna Sands Foundation, the National Fish and Wildlife Foundation, The Nature Conservancy - Vermont Chapter, the Nuttall Ornithological Club, the Philanthropic Collaborative, the Stratton Foundation, the Stratton Mountain Resort, the Thomas Marshall Foundation, the Wallace Genetic Foundation, a State Wildlife Grant through the Vermont Fish and Wildlife Department, the Vermont Monitoring Cooperative, USDA Forest Service Northeastern Research Station, U.S. Fish and Wildlife Service, the William P. Wharton Trust, and many individual donors.

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Preliminary Modeling of Bicknell's Thrush Population Growth

by Vermont Center for Ecostudies on Sep 01, 2009

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Preliminary Modeling of Bicknell’s Thrush Population Growth — Presentation Transcript