|Habitat and Ecology:
Behaviour The Rock Shag is a foot-propelled pursuit diver widely distributed in southern South America. It generally forages within 5 km of the colony, and eats a variety of primarily benthic prey. It principally forages during daylight hours, with occasional night time trips during moonlit nights when birds forage in similar locations and depths as during the day (Sapoznikow and Quintana 2002). It forages solitarily, in strictly coastal areas, and feeds at the sea bed (Punta et al. 1993). Diet At Punta Loma, Argentina, the main prey are benthic fish Riberoclinus eigenmant and the polychaete Eunice sp., both associated with sandy seafloors and seaweeds (Quintana 2001). At Bahias Bustamante and at Melo, Argentina, the species fed mainly on Rock Cod (Notothenia spp.), which were present in 87% of breeding and 91% of non-breeding regurgitated pellets (Punta et al. 1993). Foraging range At Punta Loma, Argentina, during the chick-rearing period, birds spent 36% of daylight hours away from the colony on feeding trips, and 92% of the foraging trip was spent diving (Quintana 2001). Shags fed mainly in water less than 10m deep, with a gravelly sand bottom and within 5 km of the shore (Quintana 2001). The mean foraging ranges were 3.8 ± 2.6 km and 2.6 ± 2.3 km in 1996 and 1997 respectively (Quintana 2001). These results are consistent with observations made in Bahia Bustamante, Argentina, where the observed foraging range was between 50-2000 m from the coast (Punta et al. 1993). Typically, the species forages in inshore waters less than 20m deep (Quintana 1999). Using a published relationship between dive depth and dive duration in Shags (depth (m) = (dive time (s)-35)/1.28), the mean diving depth for Rock Shags was estimated at 12.7 ± 7.5 m, with 86% of dives under 20 m (Quintana 1999). In Port Stanley Harbour, Falklands, birds foraged mainly in or just outside giant kelp beds (Macrocystis spp. and Lessonia spp.), within 50 m of shore and where the water was 1-6 m deep (Wanless and Harris 1991). Fewer birds foraged up to 100 m out, in water 7-13 m deep but not over kelp beds (Wanless and Harris 1991). The mean water depth for dives was 4.5 m (Wanless and Harris 1991). At Bahia Bustamante and Melo, Argentina, birds either foraged within bays, or else at a distance of less than 200 m from the shore and among kelp (Macrocystis pyrifera) beds (Punta et al. 1993). They foraged in areas which were 2 - 12 m deep, and contained algae (Punta et al. 1993). Foraging occurred at the bottom throughout the year, but occasionally also in mid-water during the breeding season (Punta et al. 1993). At Punta Loma, Argentina, the seabed in all the foraging areas consisted of bands of shallowly-sloping, gravelly sand sediments, with tuffs and wave cut platforms in some areas (Quintana 2001). The features of the seabed at foraging sites were consistent with the habitat requirements of the principal prey species, i.e. sandy sea floors and seaweeds (Quintana 2001). Shags used the same feeding areas during the two study years (Quintana 2001).