Territory fidelity, reproductive success and prey choice in the brown falcon, Falco berigora: a flexible bet-hedger?

Abstract

The brown falcon, Falco berigora, is one of Australia's most common and widespread raptors, inhabiting a broad array of habitats and most climatic zones across Australia. We monitored a large, marked population (44-49 pairs) over three annual breeding seasons in southern Victoria. Reproductive parameters such as clutch size and the duration of parental care were constant across years. However, there were marked differences in brood size and the proportion of pairs breeding. Both sexes of falcons were found to have high territory and mate fidelity, with only 10% of members of each sex changing territories during the study. Falcons were flexible in their choice of nest sites, using a variety of tree species and even isolated nest trees. Nest sites and territories were regularly distributed throughout the study area, with the density of the population the highest on record for this species. The diet of the population as a whole was very broad, but each pair predominantly specialised on either lagomorphs, small ground prey, small birds, large birds or reptiles. Individuals that changed territory within the study area also switched their diet according to the predominant land-use within the new territory and thus prey availability. We argue that, at the population level, broad dietary breadth, flexibility in choice of nest site, and a conservative, static breeding strategy allows the species to persist in a broad range of environments, possibly through 'bet-hedging'. At the individual level, changeable dietary specialisation, high territory fidelity, strong year-round territorial defence, confining breeding to years when individual conditions were favourable and adjusting brood sizes when required appear to be the main strategies enabling brown falcons to thrive under a variety of conditions.

Why do female Lesser Spotted Eagles (Aquila pomarina) visit strange nests remote from their own?

“…As most raptor species are found nesting in the same places year after year, it has often been assumed that individual adults are faithful both to their nesting territories and to their mates in successive years; studies with marked birds are rare however (Newton 1979;Jenkins and Jackman 1993;Forero et al 1999;Wink et al 1999;McDonald et al 2003). It is known that Lesser Spotted Eagle breeding sites are often occupied for decades.…”

Weather dictates reproductive success and survival in the Australian brown falcon Falco berigora

“…We examined several factors likely to influence the reproductive success of the Australian brown falcon ( Falco berigora , Vigors & Horsfield), a medium‐sized falcon (males: 486 g ± 5 SE, n = 69; females: 658 g ± 7 SE, n = 91) which maintains all‐purpose territory boundaries and pair‐bonds year‐round (M c Donald, Olsen & Baker‐Gabb 2003; M c Donald 2004). The population studied has a catholic diet, attributable to differences in prey availability mediated through the principal land‐use regime of each territory.…”

Relative prey size consumption in toothed whales: implications for prey selection and level of specialisation

“…Predators may selectively consume specific types or classes of prey regardless of their local abundance, making them dietary specialists, or they may feed indiscriminately on the most abundant prey in their surroundings, switching from one prey type to another as prey change in abundance, making them dietary generalists (Scharf et al 2000, McDonald et al 2003. The identification of species as dietary specialists or generalists based on how species select prey in comparison to the range available to them is a common factor in many ecological studies (Town 1980, Churchill 1994, Kutt et al 1998, Yamada & Boulding 1998, McDonald et al 2003, Bearhop et al 2004 and is the basis for measures of a species' dietary niche width (e.g. Feinsinger et al 1981, Bearhop et al 2004.…”