Geometry of Visual Recruitment by Seabirds to Ephemeral Foraging Flocks

Abstract

JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact support@jstor.org. . Wiley-Blackwell and Nordic Society Oikos are collaborating with JSTOR to digitize, preserve and extend access to Ornis Scandinavica. . 1992. Geometry of visual recruitment by seabirds to ephemeral foraging flocks. -Ornis Scand. 23: 49-62.Using geometric relationships, we calculate theoretical upper (20-30 km) and lower (0.7-6.2 km) limits to horizontal distances over which volant seabirds can be visually recruited to join Type I flocks in the open ocean. These are compared to empirical estimates for recruitment distances, obtained from chumming experiments conducted in the western Atlantic Ocean off the southeastern United States. The product of arrival times and flight speeds for individuals (n = 164) joining 10 flocks indicated that potential recruitment distances were closer to the lower theoretical limits, with a mean distance of 4.5 km when flight time and ground speed were adjusted for detection lags, wind speed, and zigzag flight. Distances and time spans for mutual attraction among seabirds have important consequences for evaluating both intraand inter-specific interactions at the community level, as well as direct implications for sampling independence during distributional surveys that employ consecutive line transects or other sequential counting methods.

Physical and biological variables affecting seabird distributions during the upwelling season of the northern California Current

“…Having spent most of their year a long way from the CCS, once birds have found highly productive waters, through olfaction perhaps, they could use visual cues to locate actual prey schools (Haney et al, 1992;Nevitt, 1999c). Although it is possible that nonProcellariiform species were attracted also to the sight of other foraging birds (Hoffman et al, 1981;Maniscalco et al, 1998), this idea was not well supported by the PCA analyses showing only weak associations between most species representing the two groups.…”

Understanding soaring bird migration through interactions and decisions at the individual level

“…showed that the mean recruitment distance to ephemeral foraging flocks was 4.5 km but could reach 20 km (Haney et al, 1992). For a social bird, the distance over which it can detect thermals will be further than for a non-social bird, see the thermal and bird detection limits in Table 2.…”

Nearest neighbors as foraging cues: information transfer in a patchy environment

“…Unlike some terrestrial birds and aquatic birds such as pelicans and avocets (del Hoyo et al 1992(del Hoyo et al , 1995, pelagic seabirds have not generally been observed to cooperate in groups when searching for and capturing prey. Instead, large aggregations of feeding seabirds are believed to result from the accumulation of independent foragers at prey patches (Hoffman et al 1981, Duffy 1989, Harrison et al 1991, Haney et al 1992, Shealer 2002. One important cue that pelagic seabirds use to find prey may be the behavior of other seabirds, a strategy called local enhancement (e.g.…”