Summary 1.We studied chick diet in a known-age, sexed population of a long-lived seabird, the Brünnich's guillemot ( Uria lomvia ), over 15 years ( N = 136; 1993-2007) and attached time-depth-temperature recorders to examine foraging behaviour in multiple years ( N = 36; 2004-07). 2. Adults showed specialization in prey fed to offspring, described by multiple indices calculated over 15 years: 27% of diet diversity was attributable to among-individual variation (withinindividual component of total niche width = 0·73); average similarity of an individual's diet to the overall diet was 65% (mean proportional similarity between individuals and population = 0·65); diet was significantly more specialized than expected for 70% of individuals (mean likelihood = 0.53). These indices suggest higher specialization than the average for an across-taxa comparison of 49 taxa. 3. Foraging behaviour varied along three axes: flight time, dive depth and dive shape. Individuals showed specialized individual foraging behaviour along each axis. These foraging strategies were reflected in the prey type delivered to their offspring and were maintained over scales of hours to years. 4. Specialization in foraging behaviour and diet was greater over short time spans (hours, days) than over long time spans (years). Regardless of sex or age, the main component of variation in foraging behaviour and chick diet was between individuals. 5. Plasma stable isotope values were similar across years, within a given individual, and variance was low relative to that expected from prey isotope values, suggesting adult diet specialized across years. Stable isotope values were similar among individuals that fed their nestlings similar prey items and there was no difference in trophic level between adults and chicks. We suggest that guillemots specialize on a single foraging strategy regardless of whether chick-provisioning and self-feeding. With little individual difference in body mass and physiology, specialization likely represents learning and memorizing optimal feeding locations and behaviours. 6. There was no difference in survival or reproductive success between specialists and generalists, suggesting these are largely equivalent strategies in terms of evolutionary fitness, presumably because different strategies were advantageous at different levels of prey abundance or predictability. The development of individual specialization may be an important precursor to diversification among seabirds.

Flight is a key adaptive trait. Despite its advantages, flight has been lost in several groups of birds, notably among seabirds, where flightlessness has evolved independently in at least five lineages. One hypothesis for the loss of flight among seabirds is that animals moving between different media face tradeoffs between maximizing function in one medium relative to the other. In particular, biomechanical models of energy costs during flying and diving suggest that a wing designed for optimal diving performance should lead to enormous energy costs when flying in air. Costs of flying and diving have been measured in free-living animals that use their wings to fly or to propel their dives, but not both. Animals that both fly and dive might approach the functional boundary between flight and nonflight. We show that flight costs for thickbilled murres (Uria lomvia), which are wing-propelled divers, and pelagic cormorants (Phalacrocorax pelagicus) (foot-propelled divers), are the highest recorded for vertebrates. Dive costs are high for cormorants and low for murres, but the latter are still higher than for flightless wing-propelled diving birds (penguins). For murres, flight costs were higher than predicted from biomechanical modeling, and the oxygen consumption rate during dives decreased with depth at a faster rate than estimated biomechanical costs. These results strongly support the hypothesis that function constrains form in diving birds, and that optimizing wing shape and form for wing-propelled diving leads to such high flight costs that flying ceases to be an option in larger wing-propelled diving seabirds, including penguins.light is a key adaptation that has evolved independently on many occasions (1). Despite the apparent advantages of flying, the ability to fly has been secondarily lost in several groups. Because a major advantage of flight is reduced extrinsic mortality (2), one hypothesis for the evolution of flightlessness posits that gains in efficiency in other locomotory modalities, such as diving, offset mortality risks in relatively safe environments. The high energy demands of flight also may be disadvantageous, particularly in habitats with low productivity (3, 4). The restriction of some terrestrial flightless birds to remote, predator-free islands with low productivity supports this hypothesis (3, 4). The reasoning seems less tenable for flightless diving seabirds that often exploit highly productive waters but are vulnerable to predation by seals, whales, and sharks. Moreover, many species of penguin travel long distances between their breeding and feeding grounds on a journey that could be made far more quickly by flying than by walking and swimming (5). An alternative biomechanical hypothesis suggests that flightlessness evolved in these birds because of a tradeoff in the optimization of wing-propelled locomotion in different media. In short, as wings become more efficient for swimming they become less efficient for flying, and vice versa. At some point, adaptations to increase swimming...

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Abstract. We explored foraging strategies used by marine animals to search for prey by examining the relative importance of information exchange and memory in a cold ocean environment from 1998 to 2000. Recent technological advances have increased our knowledge of the foraging patterns of marine predators, but few of these studies have concurrently measured prey distribution and behavior. We quantified the arrival and departure behavior of a pursuit-diving, colonial seabird, the Common Murre, Uria aalge, at two colonies on the eastern Newfoundland Shelf through observational techniques. We also measured the distribution, abundance, and behavior of the capelin, Mallotus villosus, the main prey species of murres, within foraging ranges of each colony, using hydroacoustic, vessel-based techniques. Return and departure flight directions of murres did not match at either colony during the same period. This indicated that murres departing colonies did not use information on prey distributions outside of visual range of the colony provided by the flight paths of returning flocks of birds to the colony carrying fish. High-abundance aggregations of capelin were reliably found within specific 2.25-km areas (''hot spots'') for up to two weeks within the foraging ranges of murres from both colonies (ϳ100 km). This circumstance suggests that murres could use memory to locate hot spots on the coarse scale (1-100 km) of foraging ranges from both colonies. Specific commuting routes (regular flight paths) of murres toward and away from hot spots were obvious at sea, and feeding murres consistently marked the location of capelin schools within hot spots. These distributions provided excellent conditions for murres to locate capelin schools on both coarse and fine (1-1000 m) scales by cueing to the activities of conspecifics, known as local enhancement. While central-place foraging from breeding colonies, murres likely use a mixture of memory and local enhancement to locate prey, depending on the spatial and temporal resolution of search and current prey conditions. Uncovering such behavioral mechanisms responsible for predator-prey interactions increases our understanding of linkages among trophic levels and, ultimately, ecosystem dynamics.

Key forage species lie at the core of complex marine food webs, providing essential linkages among trophic levels. We examined the interactions of an important forage and commercial fish, capelin Mallotus villosus, and its primary avian predator, the common murre Uria aalge, in the NW Atlantic. Murres are capelin specialists and robust samplers of capelin biology. During the 1990s, the coldest surface-water event in the past 50 to 100 yr occurred in the NW Atlantic (1991), and the eastern Canadian ground-fishery was closed (1992). Concordantly, the biology and behaviour of capelin has undergone very substantial changes. We examined parental food deliveries and production at the world's largest common murre colony on Funk Island off the northeast coast of Newfoundland throughout the 1990s. Murres delayed breeding and delivered smaller and lower quality capelin to their chicks. These changes, corroborated with independent fisheries data, resulted in poor condition of murre chicks, indicating significant effects of changing capelin demographics at higher trophic levels. The diets of the murre chicks indicate that the composition of the capelin population has shifted from high size diversity to mainly smaller capelin. We hypothesize that this change resulted from the elimination of the larger-sized and earlier-spawning genotype and that the NW Atlantic capelin population is exhibiting signs of reduced reproductive potential that likely reflects lower spawning biomass.