Abstract
BackgroundSkuas and jaegers (Charadriiformes: Stercorariidae) are seabirds breeding at moderate to high latitudes and some perform extensive post-breeding transequatorial migrations. Most species overwinter and perform significant portions of their migratory flyways along the Pacific coast of South America, but scant information is available on their at-sea ecology in this waters. Our aims in this study were to determine: 1) the timing of occurrence and fluctuations in abundance of skua and jaeger species, 2) their spatial distribution within the coastal zone and 3) at-sea behavior of birds, including flock size and interactions with other seabird species.ResultsBetween July 2006 and October 2013, we conducted at-sea bird counts at Valparaiso Bay (33°S) in central Chile and confirmed the occurrence of Chilean skuas (Stercorarius chilensis), Brown skuas (S. antarcticus), and Parasitic jaegers (S. parasiticus). Parasitic jaegers are regular austral summer visitors (November to March), whereas Brown skuas occur in the area only in winter (July to October). Chilean skuas were regularly recorded year-round in the area with higher abundances between late winter and early spring (August to October). Brown and Chilean skuas where observed comparatively offshore, whereas Jaegers presented a more coastal distribution, probably associated to host presence. Chilean skuas kleptoparasitized similar-sized (shearwaters and fulmars) and larger seabird species (boobies), whereas jaegers chased only smaller coastal birds (gulls and terns). Brown skuas engaged in no kleptoparasitic behaviors. All three species were observed mostly as solitary individuals.ConclusionsSkuas and jaegers showed in general a marked seasonality in their occurrence and abundance (only Chilean skua occurs year-round) and use this area as a commuting and stopover zone within their extensive migratory flyway along the southeastern Pacific.
Highlights
Skuas and jaegers (Charadriiformes: Stercorariidae) are seabirds breeding at moderate to high latitudes and some perform extensive post-breeding transequatorial migrations
The Stercorariidae constitutes a small, distinctive family of seven kleptoparasitic seabird species all regarded as within the genus Stercorarius (Remsen et al 2013), much debate exists about their systematics; sometimes, more species and a second genus are recognized within the family (Cohen et al 1997; Braun and Brufield 1998; Ritz et al 2008; Chu et al 2009)
Comparatively less is known about their movements, marine habitat use, and at-sea behavior, along the Pacific coast of South America where some species overwinter and perform significant portions of their migratory flyways (Phillips et al 2007, 2009; Kopp et al 2011)
Summary
Skuas and jaegers (Charadriiformes: Stercorariidae) are seabirds breeding at moderate to high latitudes and some perform extensive post-breeding transequatorial migrations. Skuas and jaegers are marine top predators and exert significant effects on their prey/host populations (Furness 1987a, b) Studies on these species have focused mainly on breeding ecology, kleptoparasitic behavior, and systematics. Comparatively less is known about their movements, marine habitat use, and at-sea behavior, along the Pacific coast of South America where some species overwinter and perform significant portions of their migratory flyways (Phillips et al 2007, 2009; Kopp et al 2011). After breeding during northern summer, all tundra species conduct extensive transequatorial migrations down to South American waters, both in the Atlantic and Pacific Oceans (Furness 1987a), but details on their movements and timing of migration remain largely unknown
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
