Abstract
Aggressive sibling competition for parental food resources is relatively infrequent in animals but highly prevalent and extreme among certain bird families, particularly accipitrid raptors (Accipitriformes). Intense broodmate aggression within this group is associated with a suite of traits including a large adult size, small broods, low provisioning rates, and slow development. In this study, we apply phylogenetic comparative analyses to assess the relative importance of several behavioral, morphological, life history, and ecological variables as predictors of the intensity of broodmate aggression in 65 species of accipitrid raptors. We show that intensity of aggression increases in species with lower parental effort (small clutch size and low provisioning rates), while size effects (adult body mass and length of nestling period) are unimportant. Intense aggression is more closely related to a slow life history pace (high adult survival coupled with a restrained parental effort), rather than a by‐product of allometry or food limitation. Consideration of several ecological variables affecting prey abundance and availability reveals that certain lifestyles (e.g., breeding in aseasonal habitats or hunting for more agile prey) may slow a species’ life history pace and favor the evolution of intense broodmate aggression.
Highlights
In a diverse minority of bird taxa, nestlings aggressively compete with their broodmates for food, often causing their death due to physical lesions, starvation, or eviction (Mock, Drummond, & Stinson, 1990; Mock & Parker, 1997)
In addition to the above axes of life history variation, we explore how different lifestyles affecting the ease of resource acquisition (Sibly & Brown, 2007; Sibly et al, 2012) may explain variations in the intensity of broodmate aggression
We identified the most important behavioral and life history predictors among those suggested by previous studies to directly cause nestling aggres‐ sion in raptors and other birds (adult body mass (Bortolotti, 1986a; Simmons, 1988); provisioning rate (Drummond, 2002); clutch size (Drummond, 2002; Mock & Parker, 1997); feeding method (Mock & Parker, 1997); and length of nestling period (González‐Voyer et al, 2007) using the dataset containing 57 species
Summary
In a diverse minority of bird taxa, nestlings aggressively compete with their broodmates for food, often causing their death (siblicide) due to physical lesions, starvation, or eviction (Mock, Drummond, & Stinson, 1990; Mock & Parker, 1997). A low hunting or provisioning rate (e.g., due to a low abundance or availability of prey) is the ultimate causal factor of broodmate ag‐ gression, either directly (chicks fight for infrequent or unpredictable food parcels, Drummond, 2001, 2002) and/or indirectly because food limitation causes a small clutch size (parents are limited to raise small broods if hunting rates are low, Bortolotti, 1986a; Lack, 1968; Sæther, 1994; Simmons, 2000) and slow development (i.e., a long nestling period, because it takes longer to convert prey biomass into nestling biomass, Lack, 1968) In this scenario, rather than view‐ ing body mass as a fixed constraint, it is allowed to vary in response to selection on other traits (Bennett & Owens, 2002; Partridge & Harvey, 1988). After controlling for life history traits, more aggressive species were migratory species that bred in more seasonal habitats with a highly productive breeding season
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
