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.     

Site use and fidelity in the Common Guillemot Uria aalge

The site fidelity of 470 colour-ringed Common Guillemots Uria aalge with at least 1 year of breeding experience was followed on the Isle of May from 1982 to 1993. On average, 85.7% of birds recorded breeding at a site in any year were present at the same site in the following season. Of those which did not retain their site, 35% had moved to another site, 25% were nonbreeders and 40% were not seen. Site- fidelity of birds which returned to the colony the next year was 91%. There were no significant age or sex effects, but there were significant (and unexplained) year and area effects. Most birds which changed sites moved less than 2 m. Some birds which obtained a new site improved their nesting success, but many others became nonbreeders; it is speculated that the former chose to move site, whilst the latter had been evicted.     

The importance of observer effort on the accuracy of breeding success estimates in the Common Guillemot Uria aalge

ABSTRACT

Capsule: A data-thinning approach was used to assess the effects of reducing the frequency of nest-checks on estimates of breeding success of Common Guillemots Uria aalge. Inter-year and inter-colony differences in fledging age and their implications for setting a minimum age after which a chick could be assumed to have fledged were evaluated.

Aims: To assess the consequences of reducing sampling frequency on the estimation of breeding success, and on the robustness of the assumption that breeding has been successful if a chick survives to 15 days old.

Methods: Breeding success, ages at fledging and loss of chicks were estimated from daily checks at two Scottish colonies over a six-year period. Data-thinning was used to assess the consequences of reducing checks from daily to every two or three days. Breeding success was recalculated assuming that all chicks surviving to 15 days fledged.

Results: Reducing the frequency of checks from daily to every second or third day resulted in a small but statistically significant increase in the estimate of success. Between 20% and 25% of chick losses occurred when chicks were ≥15 days old. Assuming that these chicks had fledged resulted in significant increases in breeding success.

Conclusion: Assumptions about whether or not a chick fledged had a greater impact on the estimate of breeding success than reducing the frequency of nest-checks from daily to every second or third day. There was no threshold age after which a chick could be assumed to have fledged. These findings are relevant to other monitoring schemes where there is pressure to reduce input. Sampling methods used in monitoring schemes need to be clearly stated and changes in protocols documented so that sampling effects can be incorporated into future analyses.     

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.     

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.     

Increase in frequency of the bridled morph of the Common Guillemot Uria aalge on the Isle of May, 1946–2000: a return to former levels?

Bridling in the Common Guillemot Uria aalge is a classic example of a stable ratio-cline polymorphism. Between 1946 and 2000 the frequency of the bridled morph of the Common Guillemot colony on the Isle of May, south-east Scotland, increased significantly from 3.5% to 5.9%. Demographic data collected between 1982 and 2000 indicated that the average breeding success of a pair including at least one bridled bird was 83.8%, significantly greater than 79.5% in unbridled pairs. Over the same period the average overwinter survival was 96.3% for bridled birds and 94.7% for unbridled birds, but the difference was not statistically significant. A population model showed that the increase in frequency of bridling could be accounted for as a return to an equilibrium level close to the 5.04% observed in 1936. Differences in breeding success contributed relatively little to the increase, which could be explained without recourse to differential selection pressure. The latitudinal variation in bridling suggests that bridled morphs are more cold tolerant than unbridled ones. However, the increase in the frequency of bridled birds on the Isle of May was not associated with any decrease in sea or air temperatures over the period.     

GPS tracking of the foraging movements of Manx Shearwaters Puffinus puffinus breeding on Skomer Island, Wales

We report the first successful use of miniature Global Positioning System loggers to track the ocean‐going behaviour of a c. 400 g seabird, the Manx Shearwater Puffinus puffinus. Breeding birds were tracked over three field seasons during the incubation and chick‐rearing periods on their foraging excursions from the large colony on Skomer Island, Pembrokeshire, UK. Foraging effort was concentrated in the Irish Sea. Likely foraging areas were identified to the north, and more diffusely to the west of the colony. No foraging excursions were recorded significantly to the south of the colony, conflicting with the conclusions of earlier studies based on ringing recoveries and observations. We discuss several explanations including the hypothesis that foraging may have shifted substantially northwards in recent decades. We found no obvious relationship between birds’ positions and water depth, although there was a suggestion that observations at night were in shallower water than those during the day. We also found that, despite the fact that Shearwaters can be observed rafting off‐shore from their colonies in the hours prior to making landfall at night, breeding birds are usually located much further from the colony in the last 8 h before arrival, a finding that has significance for the likely effectiveness of marine protection areas if they are only local to the colony. Short sequences of precise second‐by‐second fixes showed that movement speeds were bimodal, corresponding to sitting on the water (most common at night and around midday) and flying (most common in the morning and evening), with flight behaviour separable into erratic (indicative of searching for food) and directional (indicative of travelling). We also provide a first direct measurement of mean flight speed during directional flight (c. 40 km/h), slower than a Shearwater's predicted maximum range velocity, suggesting that birds are exploiting wave or dynamic soaring during long‐distance travel.     

Among‐colony synchrony in the survival of Common Guillemots Uria aalge reflects shared wintering areas

Spatiotemporal variation in survival may be an important driver of multi‐population dynamics in many wild animal species, yet few scientific studies have addressed this issue, primarily due to a lack of sufficiently comprehensive and detailed datasets. Synchrony in survival rates among different, often distant, subpopulations appears to be common, caused by spatially correlated environmental conditions or by movement of animals from different sites such that their ranges overlap. Many seabird populations are effectively isolated during the breeding season because colonies are widely separated, but over the winter, birds disperse widely and there may be much mixing between different populations. The non‐breeding season is also the period of main mortality for seabirds. Using mark–recapture and ring‐recovery data, we tested for spatial, temporal and age‐related correlations in survival of Common Guillemots Uria aalge among three widely separated Scottish colonies that have varying overlap in their overwintering distributions. Survival was highly correlated over time for colonies/age‐classes sharing wintering areas and, except in 2004, was essentially uncorrelated for those with separate wintering areas. These results strongly suggest that one or more aspects of the winter environment are responsible for spatiotemporal variation in survival of British Guillemots, and provide insight into the factors driving large‐scale population dynamics of the species.     

Habitat selection,diet and food availability of European Golden Plover Pluvialis apricaria chicks in Swedish Lapland

Fennoscandian alpine tundra habitats support large numbers of breeding waders, but relatively little is known about their breeding ecology despite the fact that this habitat is threatened by climate change. We studied habitat selection, diet and prey availability of European (Eurasian) Golden Plover Pluvialis apricaria chicks at the Vindelfjällen Nature Reserve, Ammarnäs, Sweden. Information from 22 chicks tracked using radio‐transmitters was analysed. By analysing 149 faecal samples, four main prey taxa were identified, Coleoptera (40%), Bibionidae (31%), Hymenoptera (13%) and Tipulidae (10%). We found that chicks switched from feeding on Tipulidae to feeding on Bibionidae as they grew, and that this switch coincided with a shift from the use of the habitat where Tipulidae were abundant (alpine meadow/heathland) to the use of the habitat were Bibionidae were abundant (Willow shrub). Although chicks track food availability to some extent, the link between prey availability and habitat use was not perfect, indicating that additional factors other than food abundance, such as shelter from predators, determine habitat selection. Bibionidae are an important prey for Golden Plover chicks as it is the only prey group that has a late summer flush in abundance, in contrast to the general decline of total arthropod biomass during the chick‐rearing period. However, Bibionidae imagoes only occurred in 2011 and were virtually absent in 2013, which relates to the species’ ecology with 2‐ to 5‐year cycles in mass occurrence. Extreme annual variation in an essential food source such as Bibionidae imagoes might have an important effect on the condition and survival of Golden Plover chicks, an important subject for future studies. The foraging conditions for Golden Plover chicks in Fennoscandia appear to be different to those in the UK, where the chicks rely mainly on a Tipulidae flush only.     

Relationship between diet composition and the fecundity of Musca domestica

A study of the relationship between diet compositions of housefly Musca domestica and the fecundity of the insect was carried out. Fecundity was increased more than 30% by adding a protein source and inorganic salts into the larval and adult diets. Also, adding a protein source into the adult diet prolonged the oviposition period of adult houseflies.     

The visual fields of Common Guillemots Uria aalge and Atlantic Puffins Fratercula arctica: foraging,vigilance and collision vulnerability

Significant differences in avian visual fields are found between closely related species that differ in their foraging technique. We report marked differences in the visual fields of two auk species. In air, Common Guillemots Uria aalge have relatively narrow binocular fields typical of those found in non‐passerine predatory birds. Atlantic Puffins Fratercula arctica have much broader binocular fields similar to those that have hitherto been recorded in passerines and in a penguin. In water, visual fields narrow considerably and binocularity in the direction of the bill is probably abolished in both auk species. Although perceptual challenges associated with foraging are similar in both species during the breeding season, when they are piscivorous, Puffins (but not Guillemots) face more exacting perceptual challenges when foraging at other times, when they take a high proportion of small invertebrate prey. Capturing this prey probably requires more accurate, visually guided bill placement and we argue that this is met by the Puffin's broader binocular field, which is retained upon immersion; its upward orientation may enable prey to be seen in silhouette. These visual field configurations have potentially important consequences that render these birds vulnerable to collision with human artefacts underwater, but not in air. They also have consequences for vigilance behaviour.     

Fish fed to young Guillemots, Uria aalge, and used in display on the Isle of May, Scotland

Guillemots on the Isle of May fed their young on Sandeels and Sprats, the proportion of the latter being highest late in the day and the season. There was a peak of feeding after dawn when many large Sandeels were brought. Weather had no effect on feeding rate but this did increase with the chicks age. Food appeared to be abundant. A large Sprat was the most efficient return for effort and Guillemots may select the most energy-rich prey. Display fish (mainly small Sandeels) were brought throughout the season, mostly by females which often ate them later. The significance of the fish-carrying display is obscure.     

The diet and growth of O-group flounder,Platichthys flesus (L.), in the River Dee,North Wales

Many O-group flounder, Platichthys flesus, live in the lower reaches of rivers in North West Europe; while there is extensive information on the niche that they occupy in estuarine and marine environments, little is known of their life in freshwater. The diet of O-group flounder in the Lower Welsh River Dee was studied by stomach contents analysis of diel and seasonal samples. The dominant prey were chironomid larvae and pupae, tubificid oligochaetes and cyclopoid copepods. There was little quantitative variation in diet temporally, although a weak crepuscular pattern of stomach fullness was shown. There was wide variation in length and weight in all months, but the mean values at age I were 60 mm and 2.9 g respectively.     

Effects of prey abundance on the foraging behaviour, diving efficiency and time allocation of breeding Guillemots Uria aalge

The foraging behaviour of Guillemots Uria aalge at sea was compared between 2 years of radically different food abundance. Radio telemetry was used to determine foraging locations and diving patterns. In the poor compared with the good food year, foraging trips were much longer, the birds foraged more than six times further from their breeding sites, they spent over five times as much time diving when at sea and their estimated energy expenditure was twice as great. Time spent foraging in the poor food year was at the expense of time spent sitting at the colony. The duration of a foraging trip was a poor indicator of distance travelled but a good indicator of the amount of time spent diving. Mean dive durations, surface pause durations and interbout periods did not differ between years, but individuals made more than four times as many dives per diving bout in the poor food year. Surface pause lengths did not vary with water depth in either year. In the poor food year, birds made shorter surface pauses for a dive of a gi^ven duration than in the good food year, possibly accepting a lactic acid debt in order to maximize searching time, The duration of the interbout period was positively related to the number of dives in the previous bout, and dives tended to get shorter in long diving sequences, suggesting possible exhaustion effects. These data demonstrate that breeding Guillemots have the capacity to adjust their foraging behaviour and time budgets in response to changes in food abundance, but this flexibility was not sufficient to compensate fully for the very low food abundance experienced by birds in this study.     

A census of the Manx Shearwater Puffinus puffinus on Skomer,Skokholm and Middleholm,west Wales

In 1997/98 a census was made of the Manx Shearwater populations on three Welsh Islands: Skomer, Skokholm and Middleholm. The census was made by counting all the burrows in the winter, playing a tape-recording of a male call (to which only males respond) down a sample of the burrows during the incubation period and applying a correction for the response rate (the proportion of males which respond). The response rate was determined by playing the tape-recordings down a set of burrows in which eggs had been laid and where the incubating birds could be examined. Knowing the total number of burrows, the number of burrows sampled, the number of responses and the response rate enabled us to make an estimate of the population size on each island. Skomer, with an estimated population of some 102000 breeding pairs is probably the largest colony of Manx Shearwaters in the world; the estimates for Skokholm and Middleholm were 46000 and 3000 respectively. These figures are compared with earlier censuses undertaken using traditional methods.