Relationship between demographics and diet specificity of Imperial Eagles Aquila heliaca in Kazakhstan

Abstract

The demographic consequences of within-population variability in predator foraging are not well understood. We assessed the relationship between the degree of diet specialization and two demographic parameters, population density and reproductive output, within a single population of Imperial Eagles Aquila heliaca at a nature reserve in north-central Kazakhstan. Nearest-neighbour distances between eagle nests throughout the reserve, and thus population density, were correlated with the degree to which diets were specialized. Diet diversity showed an extensive regional variability that was linked to prey distributions, but withinyear analyses of reproductive output did not show similar linkages. However, multi-year analyses of breeding performance showed inter-regional differences in nesting success that were paralleled, and probably driven by, similar trends in diet diversity. In contrast, brood size at fledging was not linked to diet diversity and was more probably driven by reservewide influences such as weather. Finally, the decision to initiate breeding was associated neither with diet diversity nor with environmental variability. Our results indicate that the degree of dietary specialization is linked to the demographics of Imperial Eagle populations. For these and other raptor populations, it is possible that management could be used separately to increase or decrease nesting success, brood size at fledging, and the likelihood that a pair will initiate breeding.

Intra- and inter-individual variation in the foraging ecology of a generalist subantarctic seabird, the gentoo penguin

“…Our findings are in agreement with results on a long-distance forager, the wandering albatross Diomedea exulans, demonstrating that specialist and generalist individuals had similar levels of body condition (Ceia et al 2012). No effect of specialisation on reproductive outcomes has been detected in other bird species (Votier et al 2004, Katzner et al 2005, Dehnhard et al 2016. Indeed, even though generalists may deliver somewhat less energy per day, specialisation may not have an impact on measures of evolutionary fitness (Woo et al 2008).…”

Breeding biology of Montagu’s Harrier Circus pygargus in north-central Kazakhstan

“…The area outside the Reserve boundaries was used by humans mainly for sheep, horse and cattle grazing (grazing is not authorised within the Reserve boundaries). Additionally, more than 50% of the steppe outside the Reserve was ploughed for wheat cultivation during the 'virgin lands' program initiated in the 1950s (Katzner et al 2005), so part of the area was covered by agricultural land (mainly cereal crops). Much of this area turned to fallow in the 1990s, having been neglected since the dissolution of the USSR (Katzner, 2003) Detailed quantitative data on the surface covered by these different habitat types is currently lacking, but based on semi-quantitative observations along our network of tracks, 20% of the monitored area was agricultural land, 60% was unprotected non-agricultural areas (including steppe, riverine habitats, and bushy areas, the latter not covering more than 5% of the surface), and 20% was protected areas (within Naurzum Reserve, including steppe, forest, riverine habitats, and bushy areas, the latter not covering more than 5% of the surface).…”

A proposal to define vulnerability of cetacean areas to human development: variables and analysis procedures applied to the Gulf of California

“…Areas with a higher number of species, where species are distributed in more restricted habitat ranges, where species have high diet specificity, and/or where encounters are more frequent become a priority for management and conservation in any given area or region (Katzner et al, 2005;Van Damme and Wallace, 2005;Felizola Diniz-Filho et al, 2006;Roberts et al, 2010).…”