Evidence Suggesting that Ivory-billed Woodpeckers (Campephilus principalis) Exist in Florida

The Ivory-billed Woodpecker (Campephilus principalis) disappeared from the forests of southeastern North America in the early 20th Century and for more than 50 years has been widely considered extinct. On 21 May 2005, we detected a bird that we identified as an Ivory-billed Woodpecker in the mature swamp forest along the Choctawhatchee River in the panhandle of Florida. During a subsequent year of research, members of our small search team observed birds that we identified as Ivory-billed Woodpeckers on 14 occasions. We heard sounds that matched descriptions of Ivory-billed Woodpecker acoustic signals on 41 occasions. We recorded 99 putative double knocks and 210 putative kent calls. We located cavities in the size range reported for Ivory-billed Woodpeckers and larger than those of Pileated Woodpeckers (Dryocopus pileatus) that have been reported in the literature or that we measured in Alabama. We documented unique foraging signs consistent with the feeding behavior of Ivory-billed Woodpeckers. Our evidence suggests that Ivory-billed Woodpeckers may be present in the forests along the Choctawhatchee River and warrants an expanded search of this bottomland forest habitat.

Factors driving territory size and breeding success in a threatened migratory songbird, the Canada Warbler

Successful conservation of migratory birds demands we understand how habitat factors on the breeding grounds influences breeding success. Multiple factors are known to directly influence breeding success in territorial songbirds. For example, greater food availability and fewer predators can have direct effects on breeding success. However, many of these same habitat factors can also result in higher conspecific density that may ultimately reduce breeding success through density dependence. In this case, there is a negative indirect effect of habitat on breeding success through its effects on conspecific density and territory size. Therefore, a key uncertainty facing land managers is whether important habitat attributes directly influence breeding success or indirectly influence breeding success through territory size. We used radio-telemetry, point-counts, vegetation sampling, predator observations, and insect sampling over two years to provide data on habitat selection of a steeply declining songbird species, the Canada Warbler (Cardellina canadensis). These data were then applied in a hierarchical path modeling framework and an AIC model selection approach to determine the habitat attributes that best predict breeding success. Canada Warblers had smaller territories in areas with high shrub cover, in the presence of red squirrels (Tamiasciurus hudsonicus), at shoreline sites relative to forest-interior sites and as conspecific density increased. Breeding success was lower for birds with smaller territories, which suggests competition for limited food resources, but there was no direct evidence that food availability influenced territory size or breeding success. The negative relationship between shrub cover and territory size in our study may arise because these specific habitat conditions are spatially heterogeneous, whereby individuals pack into patches of preferred breeding habitat scattered throughout the landscape, resulting in reduced territory size and an associated reduction in resource availability per territory. Our results therefore highlight the importance of considering direct and indirect effects for Canada warblers; efforts to increase the amount of breeding habitat may ultimately result in lower breeding success if habitat availability is limited and negative density dependent effects occur.