Description of Research

Previous related work by Lasha Young (2003) and Matt Betts (2005) identified Blackburnian Warbler (Dendroica fusca) as a species potentially sensitive to the amount of mature forest at the landscape scale. Many researchers believe that survival is the most important demographic parameter limiting populations (Donovan and Thompson 2001). Estimates of survival for migratory passerines are also largely unknown and what estimates do exist are generally based on small sample sizes.

The objective of this research is to determine the influence of forest management at the landscape scale on the apparent survival of a forest bird indicator species (Blackburnian Warbler) and a more abundant congener with similar habitat requirements (Black-throated Green Warbler, D. virens). Both of these neo-tropical migrant species are reported to be dependent, to some extent, on mature forest (Morse 2004, Morse and Poole 2005) and are potentially affected by mature forest reduction caused by forest management (Hagan et al. 1996). A central question of this research is: How does reduction of mature forest influence the apparent survival of two species of forest songbirds dependent on this habitat type?

Capturing and colour-banding forest songbirds is critical to this work as it potentially gives us measures of (A) age (older birds are often found in the highest quality habitat) (Holmes et al. 1996) and (B) survival (survival is higher in large patches) (Doherty and Grubb 2002). As many breeding neo-tropical migrants exhibit a high-degree of site-fidelity (Holmes et al. 1996), we can gather return rates from year-to-year for banded individuals and estimate apparent annual survival using Program MARK, a flexible capture-mark-recapture computer program. In 2005 and 2006, we also tracked a subset of our population throughout the breeding season to gather rates of within-season survival. This approach addresses the importance of events occurring on the breeding grounds as directly affecting survival. To our knowledge, we are one of the few studies incorporating this component (but see Jones et al. 2004).

Our overall strategy is to measure apparent annual survival of the two focal species along the gradient of amounts of mature forest within the 4000 km² study area: Fundy National Park (206 km²), where contiguous mature forest covers close to 80% of the landscape, and the highly-fragmented Crown Land to the north and west of the Park where percent of mature forest has been reduced to about 12-50% of the landscape. Results of this study will be used by forest managers to determine which species are sensitive to harvesting and how much forest should be left to protect these species. We will also be reporting the first estimates for both of these species based on large sample sizes.

References

Doherty, P., and T. Grubb. 2002. Survivorship of permanent-resident birds in a fragmented forested landscape. Ecology 83: 844-857.

Donovan, T.M., and F.R. Thompson III. 2001. Modeling the ecological trap hypothesis: a habitat and demographic analysis for migrant songbirds. Ecological Applications 11: 871-882.

Hagan, J., W.M. Vander Haegen, and P. McKinley. 1996. The early development of forest fragmentation effects on birds. Conservation Biology 10: 188-202.

Holmes, R.T., P.P. Marra, and T.W. Sherry. 1996. Habitat-specific demography of black-throated blue warblers (Dendroica caerulescens): implications for population dynamics. Journal of Animal Ecology 65: 183-195.

Jones, J., J.J. Barg, T.S. Sillett, M.L. Veit, and R.J. Robertson. 2004. Mininum estimates of survival and population growth for Cerulean Warblers (Dendroica cerulea) breeding in Ontario, Canada. The Auk 121:15-22.

Morse, D.H. 2004. Blackburnian Warbler (Dendroica fusca). The Birds of North America Online. (A. Poole, Ed.) Ithaca: Cornell Laboratory of Ornithology; Retrieved from The Birds of North American Online database: http://bna.birds.cornell.edu/BNA/account/Blackburnian_Warbler/.

Morse, D.H. and A.F. Poole. 2005. Black-throated Green Warbler (Dendroica virens). The Birds of North America Online (A. Poole, Ed.). Ithaca: Cornell Laboratory of Ornithology; Retrieved from The Birds of North American Online database: http://bna.birds.cornell.edu/BNA/account/Black-throated_Green_Warbler/.

Funding Acknowledgements

Fundy Model Forest

Fundy National Park

New Brunswick Wildlife Trust Fund