Reproductive Tactics of the Long-Tailed Skua Stercorarius longicaudus

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Abstract
From 1967-1979, long-tailed skuas (S. longicaudus Vieill) in a study area in north Sweden did not breed during years of low rodent abundance. In good rodent years, most or all pairs nested. When rodents were common, skuas laid 2 eggs; in medium rodent years, some pairs laid only 1. None of the total 132 clutches contained more than 2 eggs. Recoveries among 26 individually color-ringed adults indicate that long-tailed skuas have high adult survival, and are highly faithful to their traditional breeding sites. The reproductive tactic differs markedly between long-tailed skuas and snowy and short-eared owls, and other rodent specialists in the same region. The owls have much larger clutches and are probably nomadic; theoretical arguments suggest that nomadism should be favored by large clutch size. The difference in clutch size is probably related to alternative adaptations for avoiding nest predation, possibly also to different survival rates during the non-breeding season.