Applying songbird population dynamics models to conservation biology needs
A. L. Podolsky
Section: Population ecology
Proper understanding of the reproductive biology traits and population dynamics patterns of declining songbird
species is crucial for ensuring their effective protection and recovery. Metapopulation dynamics may cause the extinction
of local populations in some landscape patches regardless of the habitat quality and undertaken conservation measures.
At the same time, the source-sink type of the population dynamics could saturate lower quality habitat patches with dispersing
individuals from the population sources. Hence, poorer quality habitats presumed to yield population sinks could
eventually maintain population sources. Consequently, an effective recovery strategy for declining species should include
high quality suitable habitats along with some poorer quality patches in the regional network of protected natural areas.
I developed the mathematical model for songbird reproductive strategy based on the case study of my three-year
field research conducted on the Ovenbird (Seiurus aurocapilla L.) in the Great Smoky Mountains National Park (U.S.A.).
Breeding Bird Survey detected multiannual negative population trends in this species in pristine landscapes of the Southern
Appalachians, whereas its growing populations were found in some of the adjacent areas strongly affected by human
activities. I modified basic Pulliam’s (1988) model of population growth rates for this species by including assumptions
about annual female survival and annual fecundity. I also applied productivity data from 110 active nests to determine an
average successful brood size and nesting success. Finally, I added probabilistic variables accounting for renesting rates
after unsuccessful breeding attempt and double-brooding rates to the model while assuming equal sex ratio among the
breeding individuals. Computer simulations based on actual data and assumed range of values of the model variables yielded
population growth rates well below 1, thus confirming the declining status of the national park populations. Therefore, the
best pristine habitats in the study area were not ecologically significant sources, and in fact they were ecological traps for
this species. Such unpredictable population dynamics in high quality habitats vs. low quality patches could be caused by the
“paradox of predation”: high quality landscapes of the national park attracted, in addition to birds, a variety of mammalian
and reptilian nest predators. Most of these predators were absent or scarce in low quality
ISSN 1995-4301
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