Status and Reproductive Outcome of the Breeding Population of Striated Caracaras (Phalcoboenus australis) at Franklin Bay, Staten Island, Argentina

The dynamic trophic niche of an island bird of prey

“…We thus expect breeders' and chicks' isotopic niches to be a subset of the floaters' niche (e). During the nonbreeding season (b), while the rockhopper penguins overwinter at sea, we propose a range expansion for all age classes (d) with a predicted incorporation of new prey sources and a consequent isotopic niche expansion (f) some rockhopper penguin subcolonies have no associated caracara nests (Balza et al, 2017). Caracaras are the most abundant scavenger on the island (Frere et al, 1999), being over six times more abundant than the second most abundant species (i.e., southern crested caracara, Caracara plancus, UB unpublished).…”

“…Within its tussock ( Poa flabellata ) grasslands, our 4 km 2 study site at Franklin Bay holds a large southern rockhopper penguin colony with 127,000 breeding pairs, plus 4,600 breeding pairs of imperial shag ( Leucocarbo atriceps) and 1,600 Magellanic penguin ( Spheniscus magellanicus) breeding pairs (Raya Rey et al., 2014). Grazing pressure by introduced herbivores (goats since 1856 and red deer since 1974) has apparently restricted nest site availability for caracaras, and some rockhopper penguin subcolonies have no associated caracara nests (Balza et al., 2017). Caracaras are the most abundant scavenger on the island (Frere et al., 1999), being over six times more abundant than the second most abundant species (i.e., southern crested caracara, Caracara plancus , UB unpublished).…”

“…During the breeding season, they associate with seabird colonies, breeding in their proximity and feeding on eggs, chicks, adults, and carcasses (Catry et al., 2008; Liljesthröm et al., 2008; Strange, 1996). It is expected that, to ensure breeding success, nesting attempts are preferentially associated with (i.e., restricted to) foraging habitats that include seabird nesting patches (Balza et al., 2017; Catry et al., 2008; Strange, 1996). Floaters, although also attracted to the colonies, are likely to be excluded, or have limited access to them due to territorial behavior of breeding pairs (Figure 1).…”

Assessing the conservation value of nature reserves: terrestrial birds in Isla de los Estados (Staten Island) Provincial Reserve, Tierra del Fuego, Argentina

“…Therefore, coasts and open-lands presented more exclusive species (species with higher habitat requirements), indicator species, and greater diversity in terms of habitat use and trophic level than forests, highlighting the importance of these habitats for birds in terms of conservation value. P. australis has a very limited distribution, and is classified as Near Threatened (BirdLife International 2016) with an extant population of < 2,500 mature individuals (Balza et al 2017). Furthermore, center fjord could be considered with greater conservation value than west and east fjords because of the higher diversity indices.…”

The highest mercury concentrations ever reported in a South American bird, the Striated Caracara (Phalcoboenus australis)

“…As top predators and facultative scavengers, caracaras may be highly exposed to mercury accumulation. In particular, the resident population in Franklin Bay (Isla de los Estados) build their nests in close association with Southern Rockhopper penguins (Eudyptes chrysocome, hereafter rockhopper) and are the main predator of their eggs and chicks (Liljesthröm et al 2008;Balza et al 2017). Moreover, caracaras of all ages and breeding status depend on marine resources and particularly on penguin subsidies during breeding season (Balza et al 2020).…”