Anthony J. Gaston

Foraging Behavior and Physiological Adaptation for Diving in Thick-Billed Murres

Foraging behavior and physiological adaptations for diving were studied in Thick-billed Murres, Uria lomvia, in the field and laboratory. Electronic, light-emitting diode, and capillary recording devices were used to measure foraging behavior. Individual dives were a flattened U shape in profile, and occurred in bouts lasting 15 min. Dive patterns were nocturnal; most dives occurred between 2000 and 0400. Murres probably concentrate their foraging effort at times when prey is most available as it migrates closer to the surface in the evening as part of the deep scattering layer. Although dives averaged 18 m in depth and 55 s in duration, most time-at-depth was spent between 21 and 40 m. Thus, murres made a large number of shallow, short-duration dives. Maximum dive depth was 210 m, while maximum dive duration was 224 s. Descent and ascent rates averaged 0.94 and 0.85 m/s, respectively. Hematocrit, hemoglobin, blood volume, and pectoralis myoglobin levels were measured in the laboratory as 52.8%, 18.0 g/100 mL, 12.3% body mass, and 1.9 g/100 g, respectively. Total useable oxygen store was calculated as 44.8 mL/kg, giving an estimated aerobic dive limit (ADL) of 47 s. Murres exceeded the calculated ADL in 48% of their dives. Long-duration diving is probably a more efficient foraging strategy for murres given their relatively small size and limited oxygen storage capabilities. The observed dive depths raised questions of potential problems with decompression sickness (bends) and lung collapse.

The Effect of Age on Timing of Breeding and Reproductive Success in the Thick‐Billed Murre

A seasonal decline in reproductive success is common to many birds breeding in seasonal environments. We examined the reproductive success of Thick-billed Murres breeding at Coats Island, Northwest Territories, Canada to assess the extent to which a seasonal decline in success could be accounted for by correlations between the age of the birds and their date of laying. In 1990 and 1991 reproductive success declined with date of laying: this decline was due mainly to a decline in the proportion of eggs that hatched. No corresponding decline was found in the proportion of hatchlings that reached fledging age. Pairs containing at least one young (4- or 5-yr-old) bird laid later and hatched a lower proportion of eggs than those containing at least one older (>7-yr-old) bird. The two groups did not differ in the proportion of hatchlings reared. When looked at separately, the pro- portions of young and older birds that succeeded in hatching their egg were not affected by date of laying. When the two age groups were combined, the trends with date were similar to those found for a large sample, mostly birds of unknown age. To correct for differences in timing of laying, a sample of early breeders was induced to lay replacement eggs 14 d later. These experimental pairs were as successful as early control breeders. A greater proportion of the experimentally delayed pairs hatched chicks than birds laying for the first time at a similar date. The experimental pairs were also more successful than young birds that bred earlier. The growth of experimental and control chicks did not differ. How- ever, the 14-d-old chicks of young pairs were lighter than those of experienced breeders, suggesting poorer provisioning by the young breeders. We concluded that there was no evidence for a deterioration in feeding conditions with date and that the relationship between age and/or experience and date of laying was the most important factor in causing the decline in reproductive success with date. Our conclusions may apply to other studies of reproductive success in marine birds.

Adaptive loss of mass in thick-billed murres

Mass loss of breeding Thick-billed Murres, Uria lomvia, was examined. Adult breeders lost a significant amount of mass from incubation to chick hatching (0.032 kg in 1988 and 0.063 kg in 1989). Regression of the timing of mass loss during incubation and brooding revealed that body mass was maintained constant during incubation, was lost rapidly soon after chick hatching, and remained constant at the lower level thereafter. Murres made more than twice as many foraging trips per clay while feeding chicks than while incubating eggs, and therefore increased the amount of time spent in flight while brooding the chick. The stepwise mass loss is interpreted as adaptive in increasing flying efficiency as murres spend a greater amount of their time in flight during chick brooding. Murres may experience as much as a 25% of BMR per day energetic savings, or a reduction in the mechanical cost of flight of 9.0% to 9.5% by losing the observed 4.4% to 6.2% of incubation body mass. Murre mass loss during breeding was interpreted as adaptive in reducing the energetic cost of reproduction.

High flight costs, but low dive costs, in auks support the biomechanical hypothesis for flightlessness in penguins

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 thick-billed 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.

Population parameters of thick-billed murres at Coats Island, Northwest Territories, Canada

About 100 adult and 2,000 nestling Thick-billed Murres were banded at Coats Island annually since 1984. Intensive efforts were made in 1990-1993 to estimate the reproductive success of birds of known age and to record the band numbers of as many birds as possible. Adult annual survival, estimated from the numbers of banded birds resighted, was 87% for females and 89% for males. A capture-recapture estimate for the sexes combined gave a mean annual survival of 89%. The youngest age at first breeding was three years, 60% of birds bred at five or younger and nearly 90% at six or younger. Females started to breed about one year earlier than males. Those birds breeding at less than seven years old had a lower apparent survival rate than older breeders. Approximately 50% of chicks that left the colony were resighted again at three years or older. In each year, the mean success of pairs consisting of two experienced breeders, or of one experienced and one unbanded bird was always higher than that of pairs including young birds of relatively less experience. Reproductive success increased with age to at least nine years. The survival of breeding murres from Coats Island, and those from colonies in Greenland, both of which populations are subject to heavy hunting in their wintering area, is generally lower than survival rates of Common Murres populations in Europe and North America, where hunting pressure on breeders is lower. The proportion of birds banded as nestlings that were seen at the colony at three years or older was high compared to Common Murres in Europe. The high survival rate of young birds is apparently sufficient to offset the additional mortality caused by hunting.

Impacts of chronic marine oil pollution and the murre hunt in newfoundland on thick-billed murre Uria lomvia populations in the eastern Canadian Arctic

Abstract We developed a deterministic and stochastic age-based matrix projection population model to assess and quantify the impact of mortality caused by chronic oil pollution and legal hunting on thick-billed murre Uria lomvia populations breeding and wintering in eastern Canada. We calculate the potential population growth rate in the absence of anthropogenic mortality sources using a modeling technique that translates absolute number of birds killed from anthropogenic mortality to potential survival rates in the absence of these anthropogenic impacts. The intrinsic growth rate of the deterministic matrix based on vital rates from Coats Island (λd=1.0102), as well as the stochastic growth rate (λs=1.0098, 95% C.I. 0.9969–1.0226), matched observed population trends. Hunting mortality reduced population growth rate by 0.020 (0.012–0.039), oiling mortality reduced population growth rate by 0.025 (0.012–0.039). Combined these sources reduced the population growth rate by 0.047 (0.033–0.610). Although thick-billed murre populations are stable or slowly growing in eastern Canada, anthropogenic sources of mortality are reducing the ability of the population to grow, and increase vulnerability in these populations to changes in their environment and other pulse perturbations. Our modeling technique could be used to assess specific anthropogenic impacts on populations where a vital rates and numbers killed are known, but no long-term trend information is available.

Vocal recognition between parents and young of ancient murrelets, Synthliboramphus antiquus (Aves: Alcidae)

Vocalization is a conspicuous feature of the departure of family groups of ancient murrelets, Synthliboramphus antiquus, from their colonies. The nocturnal timing of departure and the temporary separation of adults and chicks, followed by their reunion among many conspecifics, suggest that they recognize one another by their vocalizations. In this study, the calls of adults showed greater between- than within-individual variability, indicating their potential for use in recognition. The calls of sibling chicks were similar and chick calls showed greater variability between broods than within broods. In a playback experiment in a water-filled arena, chicks given the choice of parents and non-parents calls preferentially approached the parents calls and responded to them vocally. In two trials, playback of chick calls in a cove containing many adults seeking chicks attracted the correct parents. It is likely that both parents and chicks recognize each others calls and that this ability is based on their experience with the calls prior to departure. The chicks hear their parents calls each time a parent returns to the burrow to relieve its mate. Parents hear the calls of their two chicks after they hatch, a few days before departure. A system of mutual recognition may be fundamental for the success of the colony-departure strategy of ancient murrelets.

THE RELATIONSHIP BETWEEN EGG SIZE AND POSTHATCHING DEVELOPMENT IN THE THICK-BILLED MURRE

Many nonexperimental studies have reported positive relationships between egg size and posthatching survival or growth in birds. However, these results might be confounded by underlying correlations between egg size and parental attributes. At Coats Island (Northwest Territories, Canada), in 1994 and 1995, we examined the effects of egg size and parental quality on posthatching growth in mass and wing length in the Thick-billed Murre, a colonial, cliff-nesting, Arctic seabird in which the single chick leaves the nest at a young age and at a preliminary stage of development. The relationship between egg size and parental quality was randomized by switching eggs among pairs. The size of the egg originally laid by the experimental females was used as a putative measure of their quality. The size of the egg from which the fostered chicks hatched had little effect on the rate at which they gained mass. Conversely, the rate of wing growth increased with egg size, the main difference occurring at 6–10 d of age, ...

WIND AND PREY NEST SITES AS FORAGING CONSTRAINTS ON AN AVIAN PREDATOR, THE GLAUCOUS GULL

Predators often face a trade-off between energy gain and risk of injury, and their foraging decisions should thus vary with conditions that influence this trade-off. We studied how wind speed affected the foraging decisions of Glaucous Gulls preying on Thick-billed Murres breeding on Coats Island, Northwest Territories, Canada in 1990-1992. At this colony, murres bred at varying densities on broad and narrow cliff ledges. Under calm wind conditions ( 15 km/h, gulls searched more actively and focused their aerial attacks on nest sites on narrow ledges. Aerial attacks on narrow ledges were less successful (in number of eggs or chicks taken per attack) than attacks made on foot on broad ledges. However, aerial attacks also had a lower incidence of contact with defending murres because: (1) gulls could approach ledges readily by gliding; (2) murres on narrow ledges could not turn to fend off attacking gulls without dislodging their eggs or chicks; and (3) dense groups of murres on broad ledges defended their eggs and chicks communally. Gulls foraged successfully on foot on broad ledges despite communal defense by murres, although they suffered a greater risk of being struck on the head by defending murres. Because gulls favored aerial attacks under windy conditions, we concluded that a trade-off between max- imizing energy gain and minimizing risk of injury determines foraging decisions by gulls in this system, and that this trade-off was mediated by wind.

Ingested plastic in a diving seabird, the thick-billed murre (Uria lomvia), in the eastern Canadian Arctic

Plastic debris has become ubiquitous in the marine environment and seabirds may ingest debris which can have deleterious effects on their health. In the North Atlantic Ocean, surface feeding seabirds typically ingest high levels of plastic, while the diving auks which feed in the water column typically have much lower levels. We examined 186 thick-billed murres from five colonies in the eastern Canadian Arctic for ingested plastic debris. Approximately 11% of the birds had at least one piece of plastic debris in their gastrointestinal tracts, with debris dominated by user plastics. This is the first report of ingested plastics in an auk species in Canadas Arctic, and the highest incidence of plastic ingestion to date for thick-billed murres (Uria lomvia).