Local and regional demography in a migratory forest songbird and effects of forest management intensity

  • Author / Creator
    Haché, Samuel Alcide
  • The numerical response of forest birds to habitat alteration has been well documented in North America, but the underlying demographic processes driving these changes remain largely unknown. Among species sensitive to such alterations, the Ovenbird (Seiurus aurocapilla) shows one of the largest declines in abundance following low-intensity partial harvesting in the northern hardwood forest. The main objectives of this dissertation were to: 1) document the demographic response of the Ovenbird to partial harvesting; 2) test predictions from different conceptual models of habitat selection; 3) use stable isotope analyses to obtain estimates of natal dispersal distances, and 4) model current and future population dynamics in an intensively managed forest landscape based on alternative harvesting and climatic scenarios. I provided evidence for an ideal free distribution (IFD) in Ovenbirds based on the lack of a treatment (selection harvesting) effect on per capita productivity, daily nest survival, and post-fledging survival and a lower density and productivity per unit area in recent selection cuts compared to untreated deciduous stands. From feather samples of known origin, I showed important year and age variation in stable hydrogen isotope ratios (δ2Hf). Using this information and a multi-isotopic approach (δ2Hf and δ34Sf), I showed that almost all individuals (33/35) recruited in the breeding population would be considered residents and that only 6% of individuals would have originated from within 240 km of the study area. The study area would be a demographic sink, but I also detected source-sink dynamics within the study area. Projections of the future status of the breeding Ovenbird population over a 75-year period suggest that climate change will have more negative impacts than harvesting. Also, if population size is not maintained through immigration, a large decline in abundance is expected. This dissertation provides an important contribution to fundamental and applied avian ecology. Empirical evidence for an IFD has rarely been documented and, overall, my results suggest that the Ovenbird is more resilient to moderate alteration of its habitat than previously reported. Nonetheless, land managers should consider the numerous threats to migratory birds throughout their annual cycle, including the effects of climate change.

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    Doctor of Philosophy
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