Summer diet of seabirds feeding in sea-ice-covered waters near Svalbard

Summary We describe the summer diets of four seabird species. Kittiwake (Rissa tridactyla), Little Auk (Alle alle), Black Guillemot (Cepphus grylle) and Brünnich's Guillemot (Uria lomvia) collected in sea-ice-covered waters near Svalbard. Birds collected in an area filled with young sea-ice, within the seasonal sea-ice zone, were compared with birds collected from the perennial sea-ice zone dominated by multiyear ice. Pelagic Crustacea and fish dominated the diet of birds feeding in young ice, while sympagic Crustacea and fish were most important in the diet of birds feeding in multiyear ice. Boreogadus saida was the most important fish food item. B. Saida was present in the ice in both areas, while sympagic Crustacea were lacking in the area filled with young ice. Important food items in young ice were B. saida (Black Guillemots and Kittiwakes), Cajanus sp. (Little Auks) and Pandalus borealis (Brünnich's Guillemot). B. saida (Black Guillemots, Kittiwakes, Brünnich's Guillemots), Gammarus wilkitzkii (Brünnich's Guillemot, Black Guillemot) and Apherusa glacialis (Little Auk) were most important in multiyear ice. In general, Black Guillemots and Kittiwakes fed on fish, whereas Brünnich's Guillemots fed on the larger, and Little Auks on the smaller, Crustacea. The importance of sympagic species in the diet of seabirds is thought to be closely related to the age and history of the ice in the feeding area.     

Finding your mate in a seabird colony: contrasting strategies of the Guillemot Uria aalge and King Penguin Aptenodytes patagonicus

Capsule King Penguins recognize their mates by voice, but Guillemots do not need acoustic cues even though their calls show individual variation.

Aims To determine whether the structure of Guillemot calls could allow individual recognition, as with King Penguin, and whether acoustic cues are used to locate mates among a dense mass of conspecifics at a colony.

Methods Observations were made on breeding Guillemots and King Penguins. Calls made by birds returning to their mates were recorded, the signals digitized and the calls analysed. Calls were later played back to the mates of the birds concerned and the effects noted on both them and their neighbours.

Results Both Guillemots and King Penguins emitted calls on return to the breeding site which contained individual signatures and were therefore potentially usable for mate recognition. In King Penguins, auditory recognition was essential for finding a mate, whereas in Guillemots most of the arriving birds located their mate in a dense crowd of conspecifics without the help of acoustic signals. Guillemots could differentiate neighbours from strangers without auditory cues.

Conclusion Calls are essential for the successful identification of mates by King Penguins but not by Guillemots.     

The effects of food abundance on breeding performance and adult time budgets of Guillemots Uria aalge

The breeding performance, food fed to chicks and adult time budgets of Guillemots Uria aalge were examined in a year of high and a year of low food availabiIity. There was no difference between the 2 years in reproductive success, although the rate of chick feeding, chick weight and fledging success were greater in the year of high food availability. On average, chick prey items were larger in the poor food year, but this was insufficient to compensate for the lower feeding frequency. Chick feeding frequency did not differ between days in the good year but did increase later in the season in the poor food year. Compared with the high food availability year, adult Guillemots in the year of low food availability spent much less time resting at the breeding colony. and their foraging trips were twice as long. Foraging birds tended to make several successive trips before resuming brooding duties from their mates when food supplies were good, but in the low food availability year single trips were the norm. These results demonstrate that predators experiencing reduced food supply may mitigate the effects on their reproductive output by shifting their time allocation such that more time is available for foraging.     

The Breeding of the Dipper in North Westmorland

In 1983–84, 14 radio transmitters were attached to Guillemots on the Isle of May. Those with internal tuned loop transmitting aerials, glued in the centre of the bird's back with a small amount of resin were most satisfactory. Most birds retained their transmitters for 10–20 days. The bird's behaviour was sometimes altered and ways of minimizing this are discussed. Except when they had young, three (apparently normal) breeding Guillemots spent very little time on the sea in front of their site. The maximum foraging range was smallest at this time.     

Dramatic changes in the return date of Guillemots Uria aalge to colonies in Shetland, 1962–2005

Capsule Changes in return date coincided with marked changes in population size that probably resulted in fluctuating competition for nest-sites.

Aims To document the changes in return dates over a 44-year period and to identify the factors associated with these changes.

Methods We compared changes in return date at Shetland colonies with those for the Isle of May, southeast Scotland, and with the available information on population size, the abundance of some fish species eaten by Common Guillemots and large-scale changes in the oceanography and climate of the eastern Atlantic as reflected by the winter index of the North Atlantic Oscillation (NAO).

Results Common Guillemots normally return to colonies in Shetland in late winter. However, during the 1960s return dates became gradually earlier with birds present from early October. Autumn return remained the norm for about ten years after which return dates gradually reverted back to late winter. In contrast, Common Guillemots on the Isle of May, 400 km south of Shetland, showed no marked shift, returning in October each year. There was a strong negative correlation between date of return of Shetland birds and population size, whereas on the Isle of May birds came back earlier when there was a large positive winter NAO index. There was no convincing evidence that changes in wintering areas or fish abundance influenced when birds returned to the colonies, although the fish data may not have been collected on the correct spatial scale.

Conclusion Competition for high quality nest-sites is the most likely reason for Common Guillemots returning to the colonies during the autumn and winter.     

The diet of Common Guillemot Uria aalge chicks provides evidence of changing prey communities in the North Sea

Local differences in feeding conditions have been suggested as a cause of regional variation in seabird demography but multi‐colony comparisons of diet are rare. In UK waters the main fish eaten by seabirds during the breeding season belong to three families: Ammodytidae, Clupeidae and Gadidae. Climate change and fishing are affecting these fish stocks and so probably impact on predators such as seabirds. We used standardized observations of prey brought in for chicks to make the first integrated assessment of the diet of Common Guillemot Uria aalge chicks at a UK scale. Chick diet varied markedly among the 23 colonies sampled between 2006 and 2011. Sandeels (Ammodytidae), probably Lesser Sandeels Ammodytes marinus, were the commonest prey. Their contribution to the diet varied both latitudinally and among marine regions, with the proportion significantly higher for a given latitude on the west coast compared to the east. The non‐sandeel component of the diet showed latitudinal changes, with small clupeids, probably Sprats Sprattus sprattus, predominant at southern colonies whereas juvenile gadids were the main alternative to sandeels in the north. Comparison of our Guillemot chick diet with data collected 15–30 years earlier suggests that the proportion of sandeels in the diet has decreased at colonies bordering the North Sea. No significant change was apparent in Atlantic colonies but historical data were limited. The early years of our study coincided with a population explosion of Snake Pipefish Entelurus aequoreus in the Northeast Atlantic and North Sea. Pipefish were recorded in Guillemot chick diet at several northern and northwestern colonies in 2006 and 2007 but have been absent since 2009. Spatial and temporal variation in chick diet accorded broadly with patterns expected as a result of rising sea temperatures and impacts of fishing. Guillemot chick diet could potentially be a useful indicator of changes in the distribution and abundance of forage fish.     

Common Guillemot Uria aalge parents adjust provisioning rates to compensate for low food quality

The quantity and quality of food available within the foraging area set important constraints for chick‐rearing birds, but responses to low quality are not well understood. This study explored the potential for parent birds to adjust quantity (feeding rate) and quality (energy content) in chick provisioning, by studying Common Guillemots Uria aalge on Stora Karlsö, Baltic Sea, predominantly utilizing Sprat Sprattus sprattus, during conditions of high food quantity but reduced food quality. Quality is central to reproductive success in this single‐prey loader. From the chick's perspective, provisioning rates should be increased to compensate for low food quality and to fulfil its growing needs with increasing age. However, the high energy cost of flying in Guillemots makes it important for parent birds to minimize commutes to feeding areas. Provisioning parameters were recorded during three dawn‐to‐dusk watches each breeding season from 2005 to 2013, when clupeids, presumably Sprat, constituted 98% of chick diet. Generalized additive mixed models showed that both feeding rate and size of clupeids (a proxy for energy content) varied between years and changed non‐linearly with chick age, but that there was no change within breeding seasons. Chick age and year explained 36% of the variation in feeding rate but only 2% of the variation in the size of clupeids in chick diets. We conclude that parent birds tried to adjust both feeding rate and prey size, but were less successful with the latter. A strong negative correlation was found between annual feeding rates and size of clupeids, evaluated as the differences relative to the baseline year, and adjusted for the effects of chick age. Although the differences between years were small, the relationship indicates a compensation mechanism that does not seem to impact adult survival, and by which increased feeding rates can partly counteract reduced chick energy intake when food quality is low.     

Diving behaviour of Black Guillemots Cepphus grylle in the Pentland Firth,UK: potential for interactions with tidal stream energy developments

Capsule Black Guillemots Cepphus grylle were recorded diving in the Pentland Firth to an average depth of 32 metres and an overall maximal depth of 43 metres. The majority (88%) of dives were benthic with a median dive duration of 95 seconds, and a maximal dive duration of 131 seconds. The results provide empirical evidence that Black Guillemots use depths within the water column at which tidal turbines are likely to operate. Although limited, our data suggest the potential for interactions between Black Guillemots and marine renewable energy devices.     

Survival and non-breeding of adult Common Guillemots Una aalge

Annual survival of colour-ringed Common Guillemots Uria aalge with at least 1 year of breeding experience was measured in five study areas on the Isle of May, southeast Scotland from 1982 to 1993. Annual survival averaged 94.9%. There were no significant sex, year or area differences. Between 5% and 10% of the birds known to be alive in any year did not breed, and on average such birds appeared to survive less well (87%) than breeders (95%). Non-breeding did not occur randomly within the population, and 6% of birds accounted for 47% of the cases of non-breeding. It appeared that non-breeding in Common Guillemots on the Isle of May was socially induced with most cases occurring after an individual had lost its site.     

The food of young Puffins Fratercula arctica

Although Puffins fed their young on those species of small fish that were most abundant in mid water, there was some evidence of selectivity. Sandeels and Sprats were by far the most important prey species. Rockling and Whiting were also taken but they were less suitable because of their small size and low calorific value respectively. Many of the abundant gadoid and flatfish species were not preyed on to any extent. Some years Puffins on St Kilda fed their young on Whiting but in these years chicks fledged at lower weights than in years when young were fed on Sprats. It is suggested that Puffins on St Kilda were short of the best prey species compared to those on the Isle of May and were forced to feed their young on sub-optimal food.     

The diet of black guillemots Cepphus grylle in Shetland

The diet of black guillemots Cepphus grylle (L.) was studied in Shetland between 1982 and 1985, both during and outside the breeding season. Full-grown birds consumed a wide variety of fish and invertebrate species in summer, broadly reflecting the diversity of the inshore benthic fauna. In winter a greater diversity of invertebrates was taken, which assumed increased importance in the diet as the availability of benthic fish probably declined. Chicks were fed a diet of fish, with 70–80% being sandeels Ammodytes marinus and butterfish Pholis gunnellus on the island of Mousa. Sandeels were delivered more frequently in the early morning, coincident with a peak in their feeding activity. Older chicks were fed significantly longer fish. The composition of chick diet varied significantly with date, not chick age. A seasonal decline in the proportion of sandeels in the chick diet may have reflected changes in Zooplankton abundance, but the possibility that intensive industrial fishing of sandeels had adversely affected local stocks can not be ruled out.     

Social interactions among breeding Brünnich's Guillemots Uria lomvia suggest constraints in relation to offspring vulnerability

Brünnich's Guillemots Uria lomvia are adapted to high-density breeding in large colonies on steep cliffs. Because they breed on narrow ledges, egg loss through dislodgement is an important cause of breeding failure. Fighting among breeders presumably raises the risk of accidental dislodgement. In this study, we investigated whether social behaviour among Brünnich's Guillemots shows any adaptations to reduce accidental egg loss by modifying behaviour during incubation. We found that the amount of aggression increased significantly at the time of hatching, perhaps in response to the reduced risk of breeding failure through dislodgement of a chick, compared with an egg. Allopreening followed an inverse trend, falling significantly after the day of hatch. This supports the hypothesis that allopreening is used to reduce aggressive interactions. At the same time, the frequency of allopreening was greatly increased on days when mosquitoes affected the birds, consistent with the hypothesis that allopreening is part of a defence strategy against ectoparasites.     

Nest site characteristics, duration of use and breeding success in the Guillemot Uria aalge

The fate of all eggs laid by Guillemots Uria aalge in seven study areas on the Isle of May was recorded in 12 consecutive seasons. The average success at each site was related to its physical characteristics, bird density, position on the cliff and availability of suitable habitat for ticks. The numbers of neighbours and walls, type of site, slope where the egg was incubated and distance from the top of the cliff all had a significant effect on both hatching and breeding success. Potential tick habitat had no significant effect. Much variation in hatching and breeding success remained unexplained. Sites used when the colony was less than half its current size and most frequently in the period 1984–1995 were the most successful. Since an average Guillemot pair remains together at a site for only 3–4 years. the consistently high success of many sites over a period of 10–12 years suggests that the most used sites were occupied by a succession of high-quality birds.     

Feeding area specialization of chick-rearing Adélie Penguins Pygoscelis adeliae in a fast sea-ice area

Individual feeding area specialization has been reported for several seabird species. Researchers suspect that this behaviour results in feeding and/or reproductive advantages. Adélie Penguins Pygoscelis adeliae feed in small predictable open waters in a fast sea-ice area near Syowa Station, Antarctica. Their feeding sites were determined by radiotracking both members of 20 pairs rearing chicks. Twenty-five birds repeatedly fed in distinct areas more frequently than expected by chance, while the remaining 15 birds had no significant feeding area specialization. Birds seemed to feed at sites that were closer to their most recent feeding sites than they were to earlier feeding sites. Variation in specialized area, degree of feeding area fidelity and distance to feeding sites had no significant effect on the number of feeds that a bird brought to chicks per day. Neither did the estimated mass of feeds brought per day per pair depend on feeding area specialization.     

Positional behavior ofCebuella pygmaea in Yasuni National Park, Ecuador

In terms of positional behavior, the small-bodied callitrichids are distinguished from other anthropoids by their ability to leap between and to cling to large vertical supports, feeding occasionally or frequently on sap and bark insects. In this paper, I studied the positional behavior of a group of pygmy marmosets in a hilly wet tropical forest in Yasuni National Park, Ecuador. During traveling, the animals used quadrupedal walk/bound and leaping mostly on small horizontal supports. During foraging, quadrupedal walk/bound and clambering dominated. The main foraging postures were stand and cantilever, occurring mainly on small horizontal lianas. During feeding, scansorial locomotion was used very frequently. Claw clinging was the dominant feeding posture. Furthermore, large vertical lianas and tree boles were the most frequent feeding supports. These observations would suggest that scansorial locomotion, vertical clinging, and vertical leaping are most likelynot part of the same form function complex. Vertical leaps appear to be associated with moving in the lower parts of the forest. On the other hand, scansorial locomotion and vertical clinging appear to be related to feeding on the sap of tree boles and large lianas in the lower parts of the forest.     

FACTORS GOVERNING FEEDING RATE, FOOD REQUIREMENT AND BROOD SIZE OF NESTLING GREAT TITS PARUS MAJOR

SUMMARY Observations were made on feeding rates and food-consumption of nestling Great Tits Parus major mainly in Larch plantations at lake Yamanaka, Japan. Feeding frequencies were recorded by an automatic recorder. There were marked differences between early and late broods; the feeding frequencies were twice as great in early than in late broods of the same size. No clear tendency was observed in the variations of feeding frequencies in relation to brood size. There was, however, a clear inverse relationship between the frequencies and the average size of food brought to the nests. The males' share in terms of feeding frequencies is described. These figures, however, did not follow the males' contribution in terms of weight of food, which was nearly always higher than the females'. It is pointed out that feeding frequencies are far too variable to be used as a true index of food consumption by nestlings, and are not reliable. Attempts were made to measure the weight of food; the method is described. The average weight of food brought by males was lighter in early than in later broods. The total weight of food was estimated. The trend of daily food consumption per chick was similar to that of the chick's growth curve. It was found that up to about the tenth day of the nestling period daily food-intake per chick increased linearly as body weight increased. At some nests, rate of defaecation was observed. This was at first low, but it increased steeply on the third day, with a steady increase thereafter. By comparing the rates of food intake, faeces output, and weight increment of a chick, it was found that only 20–30% of digested matter (the difference between food-intake and faeces-output was used up daily (for body temperature regulation various external effort, etc.). The factors responsible for this high efficiency of growth in nestlings are discussed. There was a clear inverse relationship between the total weight of food brought per chick per day and the brood size. This is largely because the heat-loss is greater in small than in large broods, so that a chick from a small brood in fact needs more energy to maintain its body temperature after a certain age than one from a large brood. This is discussed in detail. Factors which caused variations in size of food are discussed in relation to feeding frequencies. It is pointed out that, because of the inverse relationship between energy requirement by each chick and brood size, the total food requirement by a brood as a whole did not vary directly in proportion to the brood size. An estimation showed that a b/3 still required about 75% of the total food required by a b/8. A smaller brood is less advantageous than expected to parents feeding nestlings when they encounter adverse conditions, e.g. food shortage in the habitat, or a lack of help by their mates, etc. On the other hand, it is suggested that once they have left the nest, the food-demand by a brood of fledglings the parents have to feed, so that, in the fledging period, in times of food shortage it would certainly be advantageous to have fewer young. It is suggested that, although fledglings may consume three to four times as much food as nestlings, the parents, in providing this food, would not work proportionately harder, since the parents' efficiency of providing food could be higher in feeding the fledglings, which always follow the parents as they are hunting, than in feeding the nestlings to which food has to be brought. On this basis, the adaptive significance of the length of the nestling period in nidicolous species is discussed in relation to clutch size, brood size and food requirement.     

Predation by Ravens Corvus corax on Brunnich's Guillemot Uria lomvia eggs and chicks and its possible impact on breeding site selection

We studied the behaviour of Ravens Corvus corax taking the eggs or chicks of Brunnich's Guillemots Uria lomvia at East Digges Island, Northwest Territories, Canada. We classified the characteristics of the breeding sites attacked by Ravens according to their location on the cliffs, the width of the breeding ledge, the number of adjacent rock faces and the density of nearby breeding guillemots. Ravens selectively attacked peripheral sites near the top of the occupied area, those on narrow ledges and those with few close neighbours. The risk of predation at the most vulnerable sites was more than seven times the average. For the most part, breeding success at 419 sites near the cliff top conformed to predictions based on the observations of Raven predation. However, losses observed over 3 years suggested that more eggs fall accidentally than are taken by avian predators. We concluded that the risks of predation and of accidental dislodgement both contribute to choice of nest sites by Brunnich's Guillemots. The effect of multiple close neighbours in deterring predation by Ravens may be important in determining the density of guillemot breeding sites within the colony.     

Nest Records of the Swallow

Daytime attendance of Guillemots, Razorbills, Kittiwakes and Fulmars at colonies in east Caithness was monitored by time-lapse photography over the winters of 1982/83, 1983/84 and 1984185. Fulmars frequented the colonies over a large part of each non-breeding period but were absent for extended spells in mid-winter. Guillemot visits were infrequent and usually involved relatively small numbers. They became more frequent in February in 1984 and 1985, but not in 1983, the year of a large wreck of auks on the east coast of Britain. Razorbills and Kittiwakes were absent throughout autumn and winter and re-appeared in late February or early March. The low level of winter attendance by auks, which contrasts with reports from colonies elsewhere, was probably because few adults wintered within easy reach of the Caithness colonies.     

Assimilation efficiency of adult Kittiwakes and Brünnich's Guillemots fed Capelin and Arctic Cod

The mean assimilation efficiencies of 10 adult Kittiwakes (Rissa tridactyla) and 10 Brünnich's Guillemots (Uria lomvia) fed on Capelin (Mallotus villosus) were 77.5% and 74.4%, respectively. When fed on Arctic Cod (Boreogadus saida) they were 83.1% and 78.2%, respectively. After correction for nitrogen retention, the assimilation efficiencies decreased to 72.2%, 70.6%, 81.2% and 74.7%, respectively. Kittiwakes and Brünnich's Guillemots seem to have the same ability to utilize the energy of the different food items. The differences in assimilation efficiencies when fed two fish species was mainly related to the fat content of the fish.