A Phylogenetic Approach to Reversed Size Dimorphism in Diurnal Raptors

Several adaptive hypotheses have been proposed to account for reversed size dimorphism (females larger than males) in diurnal raptors, but no consensus has emerged. We adopted a phylogenetic approach by mapping size ratios onto Sibley et al.\u27s phylogeny for the Ciconiiformes, a diverse order that includes diurnal raptors. Reversed size dimorphism (RSD) has apparently evolved at least five times in the Ciconiiformes: four times among aerial-pursuit predators (the diurnal raptors, skuas, boobies, and frigatebirds), and once in a largely polyandrous group that includes the jacanas and phalaropes. Among diurnal raptors, RSD is likely to represent the ancestral condition, but its magnitude depends on feeding habit. It is most extreme in taxa that feed on agile, avian prey (Falconidae and some Accipitridae), and has been secondarily lost in taxa that feed on slow-moving prey or carrion (Sagittariidae and Old-world vultures within the Accipitridae). The importance of foraging mode is further suggested by the case of the Hawaiian hawk (Buteo solitarius), a highly dimorphic species that was probably restricted to agile, avian prey upon colonization of Hawaii. Comparison of the Hawaiian hawk with its putative, continental ancestor suggests that both males and females became smaller on Hawaii, but the reduction in male size was greater. This differential size reduction is not explained by an intersexual allometry among Buteo species, but may reflect constraints that set a lower limit on female size

A spatial conservation prioritization approach for protecting marine birds given proposed offshore wind energy development

There are currently no offshore wind energy developments (OWEDs) in North America, although numerous OWEDs have been proposed along the Atlantic Coast. Development pressure has been a catalyst for marine spatial planning (MSP) to identify suitable areas for OWED. However, integrating complex ecological information to guide OWED siting remains a substantial challenge. We developed spatial distribution models of marine birds from aerial surveys that we conducted from 2010 to 2012 throughout a 3800km2 area off the coast of Rhode Island. For seven groups of marine birds, we constructed either a density surface model or a presence-absence model that incorporated relevant environmental covariates. We integrated our spatial models, along with uncertainty, using spatial conservation prioritization (SCP) software. This identified sites with high marine bird conservation priority that aided evaluation of proposed OWED sites. We found that shallow nearshore waters had the highest conservation priority overall, but we also detected key offshore areas of high priority. Hypothetical OWEDs placed in conservation priority areas significantly reduced the overall distribution of focal species. Currently proposed OWED sites are located in areas of relatively low conservation priority and so would not substantially reduce the overall distribution of marine birds. This SCP approach when combined with quantitative models of bird distribution given relevant environmental covariates provides a robust framework that satisfies the principles of ecosystem-based MSP. Thus, this combined SCP-distribution modeling framework should be extremely helpful to decision makers as they evaluate proposed siting locations of OWEDs in the context of a dynamic marine system. © 2013 Elsevier Ltd

Bird Responses at Inherent and Induced Edges in the Murray Mallee, South Australia. 2. Nest predation as an Edge Effect

We assayed nest predation as an edge effect, using artificial ground nests, at inherent (naturally occurring) and induced (human-created) edges in the Murray Mallee, South Australia. Nests were constructed at distances between 0-120 m away from habitat edges. The relative predation rate on nests generally increased close to induced edges with a significant difference (P < 0.05) recorded for two out of five experiments. Predation rate at inherent edges was similar from the edge to the interior, and was lower than that recorded at induced edges. Our results suggest that increased predator numbers, activity or efficiency at locating nests occurred close to the induced edges at our study sites

The evolution of reversed size dimorphism in hawks, falcons and owls: a comparative analysis

Krüger O. The evolution of reversed size dimorphism in hawks, falcons and owls: a comparative analysis. Evol. Ecol. 2005;19(5):467-486