Egg formation and the pre-laying period of the Common guillemot Una aalge

The patterns of colony attendance of male and female Common guillemots, relative to calendar date and relative to the female's laying date during the three weeks prior to egg laying, are presented. The probability of a male being at the colony was consistently higher than that for females. Male attendance peaked in the three days before his mate laid: female attendance was lowest at this time. Examination of the yolk showed that the egg was formed over 14–15 days, with yolk deposition (of first eggs) taking 11–5 days, and a lag period (between the end of yolk deposition and laying) of 3–4 days. Yolk deposition occurred over a shorter period (9–3 days) in replacement eggs, and followed a different pattern from first eggs.     

Intercolony movement and behaviour of immature Guillemots Uria aalge

A minimum of 61 Guillemots Uria aalge ringed as chicks at other colonies was recorded at the Isle of May between 1987 and 1991 (four prior to 1990, six in 1990, 51 in 1991). Two were adults and 59 were immatures. Most of the British and Irish colonies where many chicks had been ringed were represented. Higher proportions of birds ringed at colonies relatively close to the Isle of May were observed compared to birds ringed at more distant sites. Visitors ranged in age from 2 to 5 years, with single 10- and 14-year-olds. Relatively fewer 2- and 5- than 3- and 4-year-old birds were seen. Visiting birds were usually recorded once only, significantly less often than native immatures of the same age, except for 2-year-olds. The proportion of birds occupying sites on intertidal rocks as against sites in the colony appeared to be higher compared with native birds of the same age. Visiting birds formed a substantial proportion of the immature population. Ten immature birds from the Isle of May were recorded elsewhere. Four of these had been seen on the Isle of May previously, and four were seen there subsequently. A 6-year-old hatched at Sumburgh ( c. 420 km by sea) bred at the Isle of May in 1992.     

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.     

Population status of Common Guillemots Uria aalge at a colony in western Alaska: results and simulations

Colony-wide boat-based censuses suggest that numbers of Common Guillemots at Bluff, Alaska declined markedly in the late 1970s and remained low until 1983. Annual land-based counts of study plots since 1979 generally showed no trend. However, numbers declined substantially in one study area between 1978 and 1983. Reproductive success varied considerably among years and was highest in moderately warm summers. Simulation analyses suggest that the changes in numbers cannot be attributed to changes in reproductive success several years previously. Thus, factors affecting survival, presumably in winter, are apparently implicated in the declines.     

Age-related effects on breeding phenology and success of Common Guillemots Uria aalge at a North Sea colony

Capsule: Common Guillemots Uria aalge show delayed breeding and marked age-related changes in reproductive success consistent with improved performance with experience.

Aims: To determine age of first breeding and age-related effects on breeding phenology and success of Common Guillemots.

Methods: Resighting data from a long-term colour-ringing study of Common Guillemot chicks were combined with observations of breeding phenology and success to follow the recruitment process, breeding phenology and success of 62 birds at a major North Sea colony over a 30-year period.

Results: The median age of first breeding of Common Guillemots was 6.6 years. There were no detectable costs of first breeding on return rates or the likelihood of breeding the next season but first time breeders bred later and less successfully. Age of first breeding and lifetime breeding success both varied among individuals but there was no clear optimal age of first breeding and early first breeding was not associated with higher lifetime breeding success.

Conclusions: Common Guillemots in the Isle of May population delayed breeding for 3–4 years beyond physiological maturity. The marked increase in breeding success with age was consistent with improved performance with experience rather than selection for higher quality individuals. Findings from this study will inform population models by providing improved estimates of age of first breeding and age-related changes in reproductive performance.     

The post-fledging survival of young Guillemots Uria aalge in relation to hatching date and growth

The post-fledging survival of a total of 1277 young Guillemots Uria aalge ringed in 6 years was assessed using sightings of 267 individuals back at the natal colony and recoveries of 46 ringed birds. In two years there was a significant decline in survival prospects with estimated hatching date, the first time such a trend has been demonstrated in the Alcidae. In these years pairs breeding early had a 2–3 times greater chance of having a young survive to return to the colony than pairs breeding three weeks later. Hatching date had no effect on survival prospects in the other four seasons and in none of the years did chick body condition have a demonstrable effect on post-fledging survival.     

Variation in the correction factor used for converting counts of individual Guillemots Uria aalge into breeding pairs

The correction factor k (breeding pairs/total count of birds) was measured for two nesting groups of Guillemots Uria aalge over 6–7 years. The value varied between different subgroups but there were no significant differences between groups or between years. These results, and those from other studies, suggest that a value of 0–67 is applicable to a range of colonies. Values of k for Razorbills Aha tarda were more variable. A plea is made for the presentation of original counts rather than 'corrected' figures in published work.     

The breeding biology of Guillemots Uria aalge on the Isle of May over a six year period

The breeding of Guillemots was studied in five areas of different breeding density and habitat type on the Isle of May in 1981-86. Prior to 1981 numbers were increasing at 5 6° per annum but during the study the rate of increase slowed down and from 1983 to 1986 numbers were fairly constant. Adult survival was high, with a mean minimum annual adult survival of 930% (s.e. = 03). Observations in 1986 suggested that the percentage return of colour-marked immature birds was low, with only l-6% and 5.5% of second and third year birds being seen. We suggest that poor recruitment was responsible for the levelling off in numbers at the colony.
The timing of laying was constant from year to year in 1981-85 but was later in 1986. It was significantly and inversely related to sea temperature the previous March. There was a consistent ranking in median laying dates amongst the areas, with area 1 (the highest density of birds) always earliest. However, there was no significant difference in synchrony between the areas. Overall breeding success was high (0–71-0-82 young fledged per pair). There was no consistent ranking of breeding success with breeding density, habitat type or laying synchrony.
The only aspect of Guillemot biology which changed significantly was the daily food intake of a chick which approximately halved during the study period. However, this reduction in food intake had no detectable effect on either the weight of chicks with wing lengths greater than 60 mm or the amount of time off-duty breeders spent at the site. Both of these parameters were still consistent with conditions being favourable in 1986.     

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.     

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.     

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.     

Food of young and colony-attendance of adult guillemotsUria aalge on Helgoland

The guillemot colony on Helgoland, Germany, was visited from June 5th to 21st 1990. The presence of adults and food delivery to chicks was studied on a ledge holding about 50 breeding pairs. Attendance varied through the day, with most birds present at mid-day. Food consisted only of fish, 94.6% Clupeidae (herring and sprat) and 5.4% sand-eel. On average, a chick received 2.72 fish per day. After a marked early morning peak of feeding, the number of feeds per hour levelled off to a constant rate during the rest of the day until dusk. At sea, high numbers of guillemots were present in front of the colony, with densities dropping steeply with distance. The birds are thought to forage at distances of more than 5 km away from the colony.     

Effects of testosterone on cell-mediated and humoral immunity in non-breeding adult European starlings

One of the primary assumptions of the immunocompetence hypothesisis that testosterone is immunosuppressive. Although many studiesin birds and mammals have supported this assumption, conflictingresults have been reported in a variety of species. We investigatedthe effects of testosterone manipulation on both cell-mediatedand humoral immunity in adult songbirds, European starlings(Sturnus vulgaris). Male and female starlings were wild-caught,housed in the laboratory, and implanted with either empty silasticcapsules or capsules containing testosterone. Six weeks after implantation, humoral immunity was assessed by injecting thebirds with a novel antigen, keyhole limpet hemocyanin, andmeasuring specific antibody responses 10 and 15 days latervia an enzyme-linked immunosorbant assay. Cell-mediated immunitywas assessed 7 weeks after implantation via intradermal injectionof the T-cell mitogen phytohemagglutinin into the wing web and measuring the degree of swelling 24 h later. Antibody responsesto antigenic challenge were significantly suppressed in testosterone-treatedfemales 10 days post-injection and in both sexes 15 days post-injection.Furthermore, there was a significant inverse relationship betweenindividual variability in antibody responsiveness and plasmatestosterone concentrations. Cell-mediated responses to phytohemagglutininstimulation were also significantly suppressed in testosterone-treatedmales compared to same-sex controls. Testosterone treatmentsignificantly increased plasma corticosterone concentrations compared to controls, and the possibility of this effect mediatingthe immunosuppressive effects of testosterone is discussed.The present study is among the first to demonstrate testosterone-inducedsuppression of both cell-mediated and humoral immunity in aspecies of songbird.     

Distribution of the bridled form of the Common guillemot Uria aalge in the North Atlantic

This study documents the fourth survey (198 1–1982) of bridled guillemots and provides the most complete information yet available on the distribution of the bridled form of the Common guillemot. The distribution has remained largely unchanged since the last survey (1959-60), although marked changes have occurred at a few colonies. Sea surface temperature "explains" only 35% of the variance in the proportion of bridled guillemots. Minimum air temperatures during the breeding season are much more closely correlated with bridling and "explain" 60% of the variance. No relationship exists between sea temperatures and the proportion of bridled guillemots in wintering areas. The distribution of bridled guillemots may represent the slow, southward spread of the bridled form. Alternatively, selection may favour the bridled form in cooler areas. There is insufficient evidence to distinguish between these two hypotheses, but if selection is important, the correlations with environmental factors suggests that it operates during the breeding season rather than at other times.     

Survival and habitat preferences of adult Bolitophagus reticulatus

1. Data from a 4-year mark–recapture study of the fungivorous tenebrionid beetle Bolitophagus reticulatus at a locality in central Sweden and a trapping study of the species elsewhere in the same region are used to describe the survival and habitat preferences of the species.
2. The adult beetle was found to survive for up to three winters. A minimum estimate of the yearly survival rate was 0.20.
3. The beetle was found to occur preferentially on tree trunks that were either standing or lying but only touching the ground along a minor part of their length; that were relatively thick; and that carried many Fomes fomentarius sporocarps. In contrast to previous information for this species, the beetle was found to use living sporocarps to a large extent, and not only dead ones.
4. An experiment with beetles given a choice between living and dead fungus tissue indicated that pairs of one male and one female beetle preferred living fungus while single beetles preferred dead fungus.