Foraging Area Fidelity of Individual Seabirds in Relation to Tidal Cycles and Flock Feeding

Abstract

I studied the foraging behavior of Black-legged Kittiwakes (Rissa tridactyla) using radio transmitters, remote receiving stations, and a boat to track individuals. I tested the hypothesis that individual birds exhibit foraging area fidelity. I also investigated evidence for information transfer among birds and the role of tidal cycles in foraging behavior. Flight speed, feeding methods, chick growth rates, and fledging success were similar for radio-tagged birds and birds without radio-tags, suggesting that radio-tags had no significant effect. Birds made an average of two foraging trips per day for 13 d, during a spring and a neap tide series. Twenty-four of 26 birds returned repeatedly (X = 19.2 trips) to particular areas to feed; these birds were considered faithful to a foraging area. During spring and neap tides, 17 and 14 birds, respectively, timed their foraging trips to coincide with daily tidal cycles. Foraging area fidelity indicates that kittiwakes learn and remember when and where to forage and therefore may gain local knowledge of their foraging area. Individuals possessing such knowledge may have an advantage over individuals without local knowledge. Foraging area fidelity in individuals indicates that information transfer among colonial seabirds may be less important than previously expected. Birds were selective in joining feeding flocks (13 of 35 flocks were joined). Those that were joined most often were large feeding flocks that occurred in the birds’ preferred feeding areas. Birds often fed alone (n = 26 observations) rather than with feeding flocks (n = 9 observations). Individuals of a mated pair did not forage in the same area, suggesting that information transfer regarding foraging did not occur between mates. Some mates were unable to coordinate their tidally timed foraging with nesting activities, and chicks were left unattended, which may have reduced the number of chicks fledged. Such gaps in attendance may reflect why birds such as kittiwakes have delayed maturation and poor reproductive success during the first few years of breeding.