Long-Term Reproductive Output in Western Gulls: Consequences of Alternate Tactics in Diet Choice

Abstract

Abstract. Numerous studies reveal strong, positive skews in long-term breeding performance among free-living animals, yet few studies explore the mechanisms underlying such variation. We examine the results of a 12-yr study of a population of Western Gulls, Larus occidentalis. Of 112 pairs for which we have either long-term (Ն5 yr) or lifetime reproductive output, 44% bred for only a single year, and an additional 25% bred for only 2-3 yr. A few pairs bred successfully for 6 -12 yr and showed higher average clutch size, hatching success, and fledging success within any single season than did less successful breeders. The principal trait influencing both survival and reproduction was individual diet, which consisted of a mix of human refuse and fish. A strong, positive relationship existed among the amount of fish taken, breeding life-span, and reproductive performance. Birds with short life-spans took little or no fish on an annual basis. Birds with breeding lifespans Ͼ10 yr and high breeding success took Ͼ60% fish. Diet choice was also important for successful recruitment; 90% of banded offspring returning to breed on the colony had parents that had taken predominantly fish. Diets of male, but not female, recruits were correlated with diets of their parents; 90% of male recruits banded as chicks in the colony were successful breeders, in contrast to 10% of other recruits. Despite apparent selective advantages, few recruits take a diet consisting predominantly of fish, which suggests the existence of at least two alternate tactics, i.e., highly risk-prone foraging for fish, or riskaverse foraging for refuse. This suggests that diet choice is passed between generations by means such as learning or cultural transmission from parents to offspring.

Seabird use of discards and incidental captures at the Argentine hake trawl fishery in the Golfo San Jorge, Argentina

“…Kelp gulls in Patagonia are feeding generalists (Bertellotti & Yorio 1999), and usually take advantage of fishery waste at sea (Yorio & Caille 1999, Bertellotti & Yorio 2000. Because fish is valuable in energy and nutritional terms (Pierotti & Annett 1991, Bolton et al 1992, Annett & Pierotti 1999, the consumption of waste fish is probably advantageous for kelp gull breeding success and survival, particularly for young individuals. Many kelp gull colonies have increased in number during the last 2 decades (Yorio et al 1998a), including those located within the Golfo San Jorge, and it has been suggested that the use of discards and other food sources outside their natural diet (e.g.…”

Effects of maternal traits and individual behavior on the foraging strategies and provisioning rates of an income breeder, the Antarctic fur seal

“…This could explain the longer foraging trip durations and greater time spent at sea. The greater variability in foraging effort and diving behavior seen in young females compared to the prime-aged females could also be explained by a higher proportion of lower-quality individuals in the young age classes that have yet to be selected out of the breeding population (Annett & Pierotti 1999, Mauck et al 2004, Beauplet et al 2006. Beauplet et al (2006) found that in sub-Antarctic fur seals there was a higher proportion of low-quality individuals in the lower age classes.…”

“…Few strong relationships between foraging behavior and pup growth were found, suggesting that individual differences in female foraging efficiency, and potentially differences in pup physiology and behavior, are responsible for the large variability in pup growth rates. While the Antarctic fur seals at Cape Shirreff did not demonstrate distinct foraging strategies, the variability observed in their diving behavior may persist because it allows flexibility in response to an unpredictable environment, thus facilitating reproductive success in years of marginal or low prey availability (Arnould et al 1996b, McCafferty et al 1998b, Annett & Pierotti 1999. …”

Foraging strategies are related to skull morphology and life history traits of Melanerpes woodpeckers

“…For example, concurrent changes in morphology, foraging, and diet may have resulted in changes in life history patterns. Within a species diet can influence life time reproduction and behavior patterns (Blondel et al 1991;Annett and Pierotti 1999).…”