Brent Geese Branta bernicla and Zostera; factors affecting the exploitation of a seasonally declining food resource

Brent Geese Branta bernicla wintering at Lindisfarne, northeastern England, fed almost exclusively on intertidal habitats. Their main food supply was two species of Eelgrass Zostera noltii and Zostera angustifolia. Although abundant when the birds arrived in September, this Zostera was rapidly depleted during the period October-December. Brent Goose food intake rate declined with the decreasing food supply, and the birds responded by extending the time that they spent feeding. When it was no longer possible to extend the time spent feeding (i.e. they were feeding for all of the time that the food supply was available to them), they moved away from the site. The geese fed extensively at night in order to achieve their daily feeding requirements, especially later in the season. Conversion of daily food intake to energetic intake suggested that there may have been an energetic trigger acting: the geese left the site when they were unable to satisfy their basic energy demand. No evidence was found for direct interference competition between Brent Geese and the other grazer in the system, Wigeon Anas penelope: the two species showed no spatial segregation in their feeding areas at the scale investigated nor any temporal avoidance of each other.     

Day and night feeding territoriality in Willets Catoptrophorus semipalmatus and Whimbrel Numenius phaeopus during the non-breeding season in the tropics

This study was carried out to determine whether or not, and under what conditions, Willets Catoptrophorus semipalmatus and Whimbrel Numenius phaeopus continue to defend and use their daytime feeding territories at night in a tropical environment. The study was conducted in coastal Venezuela by registering, by night and by day, the behaviour and the position of colour-marked and radio-tagged birds. Night observations were made with the use of a light intensifier.
In Willets, both territorial and non-territorial birds were observed. The use and defence of territories was observed only on sandy mud areas where Fiddler Crabs Uca cumulanta were plentiful; the soft mud sites were used only by non-territorial birds. All Whimbrel were territorial. Individuals of both species defending a given space during daytime continued to occupy and defend the same area during the night. The proportion of birds foraging at night was higher on moonlit than on moonless nights. Territorial defence involved alert postures, parallel walks, calls and the chasing of intruders. Agonistic encounters between Willets and Whimbrel and other species were rare. Willets were territorial at all states of the tide except when high tides flooded the territories. Tide had no effect on the time of feeding in Whimbrel. Moonlight was clearly the factor conditioning the occurrence of nocturnal foraging on territories by both species. Foraging strategies and the type of prey and substrata explain why the incidence of night foraging varied with moonlight in territorial Willets and Whimbrels and not in non-territorial individuals.     

Temporal resource partitioning varies with individual competitive ability: a test with Arctic charr Salvelinus alpinus visiting a feeding site from a refuge

The relationship among relative size, growth rate and diel visits into a feeding compartment were studied in Arctic charr Salvelinus alpinus , a species known for its flexible activity patterns. Individual swimming activity from a refuge compartment into an uncovered feeding compartment was studied using an automated passive integrated transponder system. Approximately half of the individuals in four groups of S. alpinus spent 70–80% of their time in the feeding compartment, regardless of the time of day. The remaining individuals spent nearly as much time (70–80%) in the feeding compartment during the night, but only spent c. 20% of their time in the feeding compartment during the day. These individuals had a lower mean ± s . d . masses (13·17 ± 4·34 g) and growth rate (daily growth coefficient, G = 0·80 ± 1·19) than those individuals that spent most of their time in the feeding compartment during the day (mass = 16·65 ± 5·73 g and G = 2·04 ± 0·81). This indicated that some smaller fish were absent from the feeding compartment during daytime, possibly to avoid aggression from larger conspecifics. In the open compartment, the aggressive interactions were more frequent in daylight than during night and always low in the covered compartment.     

Dark-bellied Brent Geese Branta bernicla bernicla, as recorded by satellite telemetry, do not minimize flight distance during spring migration

Nine Dark-bellied Brent Geese Branta bernicla bernicla were equipped with satellite transmitters during spring staging in the Dutch Wadden Sea in 1998 and 1999. The transmitters (in all cases less than 3% of body mass) were attached to the back by a flexible elastic harness. One juvenile female was tracked to the Yamal peninsula in 1998. Eight adult males were selected from a single catch of 75 to span the range of body mass observed on the date of capture (11 May 1999) and all but the lightest individual completed the first lap of the migratory flight to the White Sea, Russia, according to the time schedule normal for the species. Six birds were successfully tracked to Taymyr for a total distance averaging 5004 km (range 45775164) but judging from later movements none bred (although 1999 was a breeding year). Although the routes chosen during spring migration were closely similar, none of the tagged birds migrated together. On average the geese used 16 flights to reach their summer destinations on Taymyr. The longest uninterrupted flights during the first half of the journey (Wadden Sea to Kanin) covered 1056 km (mean of seven adult males, range 7681331), while the corresponding value for the second half of the migration (KaninTaymyr) was only 555 km (mean of six adult males). Only 7% of total time during spring migration was spent in active flight, as contrasted to c.  80% at long-term stopovers. Overall average travelling speed was 118 km/day (range 97148). Including fattening prior to departure the rate of travel falls to 62 km/day (range 4970), in keeping with theoretical predictions. Routes followed deviated from the great circle route, adding at least 700 km (16%) to the journey from Wadden Sea to Taymyr, and we conclude that the coastal route is chosen to facilitate feeding, drinking and resting en route instead of minimizing total flight distance.     

Do bird captures reflect migration intensity? – Trapping numbers on an Alpine pass compared with radar counts

A limitation of standardized mist netting for monitoring migration is caused by the lack of knowledge about the relationship between trapped birds and birds flying aloft. Earlier studies related nocturnal radar counts with trapping data of the following day. In this study, we compared for the first time data gathered simultaneously by radar and mist netting, separately for diurnal and nocturnal migration. Trapping numbers were strongly correlated with migratory intensities measured by radar (r>0.6). A multiple regression analysis, including wind speed and wind direction explained 61% of variation in the number of captures. During the night, and particularly with favourable winds, birds flew at higher altitudes and hence escaped the nets to a higher proportion. The number of nocturnal migrants trapped during daytime was well correlated with migratory intensities observed by radar in the preceding night. The diurnal time patterns, however, revealed fundamental differences between trapping counts and radar observations. This was mainly due to increasing and decreasing flight altitudes in the course of the night, and by the limitations of the radar technique that underestimates migratory intensities during the day when birds aggregate in flocks. In relation to the migratory intensity recorded by radar, diurnal migrants are trapped in a much higher proportion than nocturnal migrants. Finally, our results confirm that trapping data from a site hardly used for stopover are well suited to represent the ongoing migration during the day and night.     

Phenology of migration and use of wintering sites by the increasing population of dark-bellied brent geese Branta bernicla bernicla

During the recovery of the population of dark-bellied brent geese Branta bernicla bernicla , traditional wintering sites in Britain have experienced increases in numbers and new sites have been colonized. Goose counts were used to describe the migration phenology and winter use of Scolt Head, north Norfolk (a traditional site) and the Burry Inlet, South Wales (a relatively new site) over the period of re-colonization and colonization, respectively. During the 1950s, only a few hundred birds wintered at Scolt Head, and most stayed for only a short period. By the late 1980s/early 1990s, numbers had reached several thousands, their period of stay was longer and there was little variation between years in median arrival (28 October) and departure (11 March) dates. A similar process was observed during the entire colonization phase at the Burry Inlet; initially birds arrived late and departed early, but arrived progressively earlier and departed later as wintering numbers increased. The autumn arrival rates at both sites were slower than the spring departure rates. During years of good breeding productivity, those adults with young arrived slightly later in Norfolk than failed breeders and non-breeders, and a higher proportion of young birds remained in spring after the main departure. However, the overall pattern of arrival and departure did not vary according to whether there had been a good or poor breeding season. Some adults of breeding age also remained until May. The effects of food depletion and use of novel feeding habitats in relation to migration phenology and winter use of sites are discussed.     

Foraging activity of the sand beach isopod Scyphax ornatus Dana

Abstract

The terrestrial isopod Scyphax ornatus lives on exposed sand beaches. Adult isopods spent the daytime in burrows near the high water mark and made nightly foraging excursions over the uncovered middle beach. Hourly records of their night time distribution showed that Scyphax congregated near the water’s edge during the last 4 h of flood tide, where they fed on carrion. Insects (mostly drowned honey bees) were the main food item, but coelenterates, amphipods, crabs, and goose barnacles were also eaten. During ebb and early flood tides Scyphax occurred at low densities over the uncovered middle beach. Analysis of the distribution of large and small food items on the beach showed that by feeding during the flood tide, Scyphax exploited a rich concentration of carrion that accumulated in the swash zone and that was moved slowly up the beach by the incoming tide.     

Water depth selection, daily feeding routines and diets of waterbirds in coastal lagoons in Ghana

Water depth requirements, diet, feeding styles and diurnal activity patterns are described for waterbirds using two brackish water lagoon systems in coastal Ghana, the Songor and Keta Lagoons. We project the habitat and activity data on a guild structure defined on the basis of individual feeding style and the sensory mechanism used to detect food. A total of 3199 flocks containing 118,648 individuals of 36 different waterbird species were examined during October-November 1994. Feeding habitats varied from dry mudflats to wet mud and shallow water of not more than 20 cm. The depth of water selected by waterbirds for foraging (but not for roosting) was correlated with tarsus length. Foraging birds exhibited a wide range of feeding styles using visual and/or tactile means for detecting prey: pecking, probing, stabbing, sweeping and ploughing, sometimes feeding singly, communally or socially in loose or dense flocks. Prey items taken ranged from seeds of Widgeongrass Ruppia maritima to invertebrates (mainly polychaetes, molluscs and crabs) and fish, mainly juvenile Tilapia. The daytime was spent on two main activities, feeding and roosting, with a small fraction of the time (average of 10% for 25 species) spent on comfort activities. The waterbirds exhibited either a circadian (most waders, except Common Sandpipers Actitis hypoleucos and Turnstones Arenaria interpres) or a diurnal foraging activity pattern (herons and terns), with no purely nocturnal species. Some species fed throughout the day, others showed peak foraging at various times of the day. The proportion of time spent foraging was related to guild (highest in visual and tactile surfaceforaging waders) and was negatively correlated with the size of the species. We conclude that the observed patterns in the use of the 24-h day by waterbirds for foraging are not species specific but vary depending on conditions on the feeding grounds. Nocturnal foraging is a normal and a regular strategy used by waterbirds to obtain enough food to fulfill their energetic requirements, so that irrespective of the sensory mechanism used to detect prey and the conditions prevailing on the feeding grounds, waterbirds forage day and night as dictated by their energetic needs. Water depth appears to be the key environmental factor controlling the availability of food for the waterbirds in the Ghanaian lagoons.     

DHEA levels and social dominance relationships in wintering brent geese (Branta bernicla bernicla)

After testosterone, dehydroepiandrosterone (DHEA) is the main hormone involved in aggressive behaviour in birds. While the role of DHEA has been verified for wintering territorial passerines, it has not been shown for gregarious species. In wintering geese species, both sexes present very low testosterone levels and aggression in a non-sexual context is not testosterone-related. Therefore, testosterone does not seem to be responsible for aggressive behaviour by geese during winter and the role of DHEA must be explored. We used brent geese (Branta bernicla bernicla) to examine the roles of testosterone and DHEA in dominance relationships. For the first time, we highlighted the presence of plasma DHEA in free-living geese. As the level of DHEA was lower than that of testosterone, and there was no obvious impact of DHEA level on dominance status, our results failed to confirm the role of plasma DHEA in the social hierarchies of this species during winter. Nevertheless, because DHEA levels were greater in singletons than in paired birds, we discuss the need to explore hormonal and/or behavioural mechanisms implicated within dominance status acquisition and maintenance within each reproductive status class, to underline the role of the presence of relatives as a signal of dominance abilities. We also acknowledge and discuss the possibility that the long handling time may have affected DHEA levels and masked subtle differences between individuals.     

Activity patterns, feeding and burrowing behaviour of the crab Ucides cordatus (Ucididae) in a high intertidal mangrove forest in North Brazil

Activity patterns, feeding and burrowing behaviour of the economically important semi-terrestrial mangrove crab Ucides cordatus (Ucididae, L. 1763) was studied in a high intertidal Rhizophora mangle forest stand in Bragança, North Brazil. Video observations in the rainy and dry season were conducted over 24 h cycles at different lunar phases to investigate the behaviour of these litter-feeding crabs outside their burrows. During the rainy season, crabs stayed inside their burrows for 79% and 92% of the time during day and night, respectively. Time spent for feeding, burrowing and other activities outside their burrows was significantly longer during the day with 9.9% (night: 1.7%) and at waning and waxing moon with 9% (full and new moon: 0.9%). At neap tides (no tidal inundation) foraging and feeding activities outside burrows were clearly light-dependent, increasing at dawn and decreasing at dusk. Highest activities during daytime relate to the visual localisation of food. During the dry season, crabs spent less time inside burrows at neap tides than during the rainy season (80% and 91%, respectively). However, time spent for feeding activities was similar during both seasons. During almost all observation periods crabs collected leaf litter, but rarely fed on it outside burrows. At neap tides nearly all available litter was collected, suggesting that the U. cordatus population is litter-limited during these times. At spring tides (regular tidal inundation) the surface activity of U. cordatus was tide-dependent. Crabs closed their burrow entrances 2-3 h before flooding and re-emerged as soon as the tide retreated. During the day, burrow maintenance was the second most frequent behaviour after feeding. Agonistic interactions were regularly observed and were mainly related to burrow defence. The mean foraging radius of the crabs was only 19 cm (max: 1 m) underneath high Rhizophora mangle trees where crab densities were high. The results point to a high competition for burrows and show that U. cordatus is territorial. It is concluded that several exogenous factors, in particular light, leaf litter availability, flooding of burrows and the presence of conspecifics are important in controlling the crabs' activity patterns.     

Energetic demands during brood rearing in the Wheatear Oenanthe oenanthe

Daily energy expenditure of Wheatears Oenanthe oenanthe during the brood rearing period was measured using the doubly-labelled water technique. The average daily metabolic rate (ADMR) (± 1 s.d.) for 24 individuals was 6.24 ± 1.17 cm³ CO₂/g/h, which corresponds to 95.3 ± 17.0 kJ/day (RQ = 0.75) for a bird of average mass (24.3 g).
There were no significant differences in daily energy expenditure between the sexes, nor between first-year and older birds. Individual males with longer tarsi had lower ADMR but raised larger broods. The ADMR increased at lower ambient temperatures, but this effect disappeared when the positive correlation with rainfall was taken into account. There was no relationship between the natural brood-size and parental daily energy expenditure. A positive correlation between ADMR and the time spent hopping and pecking suggests that foraging activity may account for some of the variability between individuals. The daily change in body-mass was not related to either the individual's age or its sex, and overall was not correlated with the level of daily energy expenditure. For birds examined on the same day, individuals with a higher ADMR had a greater loss of body-mass, which appears to be a high risk strategy. However, Wheatears also exhibited an ability to increase body-mass in conjunction with a drop in their daily energy expenditure.     

Diel feeding patterns of the congiopodid fishHypodytes rubripinnis in Aburatsubo Bay,Japan

Diel changes in the feeding intensity and diet composition of the congiopodid fishHypodytes rubriphnnis were studied in Aburatsubo Bay, Miura Peninsula, Japan, on July 24 and 25, 1985. In samples taken at night, the ratio of stomach content weight to body weight was high and the frequency of occurrence of fish with empty stomach was very low, while the reverse was the case in the daytime, suggesting that this species feeds intensively at night, instead of during the day. Gammarids were the most dominant prey and isopods and caprellids were next important. These three prey items accounted for 91% of the total diet by number. The proportion of isopods in the total diet showed the most remarkable diel change. They amounted to about 30% at night, but were not consumed in the daytime.     

Wintering site fidelity and movement patterns of Western Sandpipers Calidris mauri in the San Francisco Bay estuary

Western Sandpipers Calidris mauri are the most numerous shorebird species in the San Francisco Bay estuary during winter. A sample of 106 Western Sandpipers was captured in mist nets and radio-marked with 1-g transmitters to examine their wintering site fidelity and movements. Differences in distances moved, home range extent and core area size were examined by age, sex, season, site, time of day and tide. All birds remained in the south San Francisco Bay region during winter and exhibited strong site fidelity, with a mean home range of 22.0 km² or only 8% of the study area. First-year birds had larger home ranges (26.6 ± 3.6 km²) than adults (17.2 ± 2.5 km²) in winter, but home range sizes of males and females were not significantly different in any period. Home range sizes were similar between seasons, but core areas were smaller in spring (6.3 ± 1.2 km²) than in early (9.6 ± 4.0 km²) or late (11.6 ± 1.6 km²) winter. Movements and home range size were similar for radio-marked birds located during day and night. The high degree of regional and local site fidelity demonstrated that the mixture of natural mud fiats and artificial salt ponds in southern San Francisco Bay provided sufficient resources for large wintering populations of Western Sandpipers.     

The daily pattern of autumn bird migration in the northern Sahara

The temporal pattern of migration by passerine birds during the night, and their arrival during the day at the Egyptian coast and in the northern Sahara Desert was investigated. The mean direction of nocturnal migration at the coast was south-southeast, while at all desert sites it was south-southwest.
Birds arrived at the Egyptian coast only during the second half of the night which is explained by the fact that no birds could have taken off from the Mediterranean Sea. At least some of the birds landed at the coast where they spent the day before taking off shortly after sunset. These birds passed the desert sites at the expected time of day assuming a ground speed of 18 m per second. However, the origin of the birds passing the desert sites early at night is unclear. They must either have spent the day in the desert north of the study sites or they had overflown the Egyptian coast in the afternoon without landing.
The landing of birds during the day at the desert sites was bimodal. This pattern of arrival is explained either by some birds having landed at the Egyptian coast in the early morning before continuing, or by deteriorating conditions later in the day during flight or when resting in the desert, that obliged them to seek shelter at the desert sites.
A correlation between the number of migrants observed during the night and the number of resting birds in the desert on the following day suggests that an unknown proportion of birds might regularly use an intermittent migratory strategy that includes rest periods by day when crossing the desert, whereas others might adapt a non-stop migratory strategy.     

Breeding of waders (Charadrii) and Brent Geese Branta bernicla bernicla at Pronchishcheva Lake, northeastern Taimyr, Russia, in a peak and a decreasing lemming year

During summer 1991, lemmings occurred at high densities in Arctic tundra at Pronchishcheva Lake in the northeastern Taimyr Peninsula, whereas, in 1992, lemming densities were substantially lower and decreased further during the summer. In 1991, avian predators such as Snowy Owls Nyctea scandiaca, gulls and skuas bred well; Arctic foxes Alopex lagopus were rarely observed in the study area but bred in the immediate vicinity. In both years there was a late thaw, but this did not deter breeding by birds. The insect food supply for waders showed similar patterns of abundance in both years. In 1991, 73 nests of nine species of wader were found within a 14-km² study area, and Dark-bellied Brent Geese Branta bernicla bernicla nested in association with Snowy Owls. The overall density of wader nests was estimated to be 7 per km². Clutches disappeared at only two wader nests and no Brent Goose nests, and the Mayfield estimate of the daily probability of predation for waders was 0.0022. In contrast, the daily probability of predation was 0.20 in 1992, when there was a similar breeding density of waders. Arctic foxes were seen searching for food daily within the study area, and fox droppings were found associated with nests taken by predators. The predicted scenarios for peak and decreasing lemming years (the Roselaar-Summers hypothesis), i.e. low predation and high nest success in the peak year and high predation and low nest success in the decreasing year, therefore occurred.     

The ecology of dippers Cinclus cinclus (L.) in relation to stream acidity in upland Wales: time-activity budgets and energy expenditure

Summary The time-activity budget and energy expenditure of a riverine bird, the dipper Cinclus cinclus, was studied from March 1988 to July 1989, across a range of streams of contrasting acidity in upland Wales. Differences in time-activity budgets of birds on acidic and circumneutral streams were consistent with documented differences in prey availability and diet. Birds spent a significantly greater proportion of their active day foraging, swimming and flying, and less time resting, on acidic streams. Activity measurements varied significantly through the year, through the day, and with river flow. Despite differences in time budgets, mean Daily Energy Expenditure (DEE) on acidic streams was only 4.5–7.0% greater than on circumneutral streams. However, rates of energy gain were greater for dippers on circumneutral streams for every month of the year, a pattern confirmed by differences in body condition. By spending more time feeding, dippers on acidic streams will have less time for other activities such as self-maintenance and predator surveillance; they may also be less able to meet the additional demands accompanying the initiation of breeding. These findings are discussed in relation to the feeding ecology and breeding performance of dippers on streams of contrasting water quality in upland Wales.     

四川梅花鹿春季昼夜活动节律与时间分配

1997年4月,在四川铁布自然保护区用直接观察法对220头次四川梅花鹿群的昼夜活动节律和时间分配进行了观察。结果表明,鹿群春季昼夜活动的规律性较强。白昼,鹿群活动呈现明显的双峰型,2个高峰时段为08：30和19：30前后,活动频率分别为71．9％和94．13％,其他时间多处于休息状态;鹿群夜间活动强于昼间,活动频率均在6l％以上,仅在半夜01：30前后有一个相对不活跃期。同时发现,春季活动高峰期约90％的活动时间被四川梅花鹿用于采食和移动。这可能与光照、食物及人类活动的影响有关。     

Variability and stochasticity of meal size and feeding frequency in the Little Sheanvater Puffinus assimilis

The pattern of chick feeding in Little Shearwater Puffinus assimilis on Selvagem Grande was examined by weighing chicks at 4–h intervals throughout eight successive nights and daily for a further 11 days (19 days in all). Individual meals fed to chicks averaged 23.2 g (s.d. ±4.7) or 13.6% of adult mass. Mass increments over 24 h (NET) were linearly related to the sum of positive mass increments over 4–h intervals during the night (SUM) by the equation NET = 0.36SUM - 5.89 (r²= 0.60). Using this relationship, I estimated that over a period of 18 nights, a mean of 95% of chicks were fed each night, and the mean interval between feeds was 1.05 nights, with a maximum of three nights. There was no significant day-to-day variation in feeding rate. These results were not compatible with the prevalent idea that the purpose of large fat deposits in Procellariiformes is to tide chicks over periodic fasts resulting from poor feeding conditions. On average, chicks required 16 g of food per day to maintain constant mass and converted 33% of their intake of food above this requirement into biomass. Meal size and feeding frequency were independent of chick size and body condition (body-mass corrected for body-size), and the masses of food received by individual chicks each night varied in direct proportion to previous values. These results suggest that the rate of food supply to chicks was not regulated by adjustment according to chicks' nutritional requirements. To some extent, this supports the hypothesis that lipid accumulation among Procellariiformes is related to stochastic variation in food supply rate, resulting from an absence of regulation of feeding. However, feeding was not stochastic, in that adults tended to deliver consistent amounts of food to their chicks, and the pattern of feeding among even the worst-fed chicks was inconsistent with a need for large lipid stores based upon chance variation in food delivery.     

Daytime activity budget of an alpine ungulate (Tatra chamois <Emphasis Type="Italic">Rupicapra rupicapra tatrica</Emphasis>): influence of herd size,sex, weather and human disturbance

Environmental factors have strong influence on activity of alpine ungulates. However, the presence and activities of people in high mountains have been growing rapidly and have led to the advent of human-induced factors, which may modify the time budget. In this study, we examined the influence of natural and human-induced factors on the daytime budget of Tatra chamois Rupicapra rupicapra tatrica. On average, chamois spent 46% of their time foraging, 40% resting, 13% moving around and 1% on social behaviour. The amount of time devoted to particular categories of behaviour was influenced by the time of day, herd size, weather conditions and human disturbance. Human disturbance and the time of day had the highest effect on the proportion of foraging in the daytime budget, which increased as the day progressed and at greater distances from the nearest hiking trail. These two factors also increased the amount of time spent resting, which peaked during the afternoon hours and at greater distances from the nearest trail. The time spent moving around decreased with increasing herd size, distance from the nearest trail and as the day progressed. Males devoted less time to foraging and more to resting and moving around than females. The intensity of human-induced factors is particularly important for a population inhabiting a small, isolated area, as is the case with strictly high-mountain species.     

Patterns of GPS tracks suggest nocturnal foraging by incubating Peruvian pelicans (Pelecanus thagus)

Most seabirds are diurnal foragers, but some species may also feed at night. In Peruvian pelicans (Pelecanus thagus), the evidence for nocturnal foraging is sparse and anecdotal. We used GPS-dataloggers on five incubating Peruvian pelicans from Isla Lobos de Tierra, Perú, to examine their nocturnality, foraging movements and activities patterns at sea. All instrumented pelicans undertook nocturnal trips during a 5–7 day tracking period. Eighty-seven percent of these trips (n = 13) were strictly nocturnal, whereas the remaining occurred during the day and night. Most birds departed from the island after sunset and returned a few hours after sunrise. Birds traveled south of the island for single-day trips at a maximum range of 82.8 km. Overall, 22% of the tracking period was spent at sea, whereas the remaining time was spent on the island. In the intermediate section of the trip (between inbound and outbound commutes), birds spent 77% of the trip time in floating bouts interspersed by short flying bouts, the former being on average three times longer than the latter. Taken together, the high sinuosity of the bird''s tracks during floating bouts, the exclusively nocturnal trips of most individuals, and the fact that all birds returned to the island within a few hours after sunrise suggest that pelicans were actively feeding at night. The nocturnal foraging strategy of Peruvian pelicans may reduce food competition with the sympatric and strictly diurnal Guanay cormorants (Phalacrocorax bougainvillii), Peruvian boobies (Sula variegata) and Blue-footed boobies (S. nebouxii), which were present on the island in large numbers. Likewise, plankton bioluminescence might be used by pelicans as indirect cues to locate anchovies during their upward migration at night. The foraging success of pelicans at night may be enhanced by seizing prey close to the sea surface using a sit-and-wait strategy.