Chick-rearing Period Research Articles

Summer sandeel consumption by seabirds breeding in the Firth of Forth, south-east Scotland

The industrial fishery for lesser sandeels (Ammodytes marinus) is currently the largest single-species fishery in the North Sea and this species is also the main food of many seabirds breeding in colonies in this area. It has been suggested that inshore sandeel fisheries could have adverse consequences for local seabird populations. One potential area of concern is the fishing grounds on the banks (Wee Bankie and Marr Bank) which lie approximately 40 km oV the coast of south-east Scotland, well within the feeding range of many seabirds breeding at colonies in and around the Firth of Forth. A bioenergetics model is used to estimate that seabirds associated with these colonies consumed 6000‐17 000 t of sandeels during each of the summers of 1996 and 1997, with the majority of the fish being in the 1-group or older age categories. Distributions of birds at sea recorded during a systematic survey during the breeding season demonstrated that the Wee Bankie was an important feeding area for guillemot (Uria aalge), razorbill (Alca torda), and kittiwake (Rissa tridactyla) and to a lesser extent puY n( Fratercula arctica) indicating that the exploitation of sandeels by these species shows strong spatial overlap with the industrial fishery. In contrast, shags (Phalacrocorax aristotelis) and common/arctic terns (Sterna hirundo/paradisaea) showed predominantly inshore distributions while the North Atlantic gannet (Morus bassanus) probably fed mainly outside the area surveyed. Species-specific comparisons of the estimated size of the observed at-sea populations with those predicted from the number of individuals associated with colonies in the area suggests that during the chick-rearing period a high proportion of the Firth of Forth guillemot population was feeding in the surveyed area. However, for the other species the number observed at sea was consistently lower than predicted. The size of the sandeel stock associated with the Wee Bankie is currently unknown. Comparison of the size of the annual catch of the fishery and the amount taken by seabirds indicates that in most years the former has been consistently higher than the latter. Thus the potential for the fishery to aVect seabirds is likely to be greater than the converse. ? 1998 International Council for the Exploration of the Sea

Flexible foraging strategy of Cory's shearwater,Calonectris diomedea, during the chick-rearing period

Procellariiformes are well known for their low rates of food provisioning to their slow-growing chicks. In some species, the patterns of food delivery to chicks have been deduced from changes in their weight, obtained from periodic weighings. However, the behaviour of individual parents cannot be resolved using this method. In this study, we used a periodic weighing protocol with Cory’s shearwater chicks on Selvagem Grande island, in the northeast Atlantic. In addition, we used an automatic logging system to examine the attendance of individual parents. In 1997, the chicks were fed infrequently, and were in significantly poorer condition, than in other years and at other colonies. This suggests that the adults were experiencing some difficulties in finding an adequate food supply close to the colony. Under these conditions, individual parents adopted a dual provisioning strategy, making both short and long foraging trips, a previously undescribed behaviour in any northern hemisphere petrel species. Although meals delivered to chicks were larger after long trips than after short trips, the average amount of food provisioned per day spent at sea decreased with increasing trip length, and so chicks did not benefit from longer trips. This finding suggests that long trips can be used to restore the adult’s body condition, presumably depleted during short trips as shown previously for some petrels and albatrosses. The adoption of this flexible foraging strategy, which differs from the uniform intervals observed in Cory’s shearwaters experiencing situations of ‘normal’ food abundance, may represent a mechanism through which breeding birds compromise between the needs of their chicks and the maintenance of their own body condition.

The movements of gentoo penguins Pygoscelis papua from Ardley Island, Antarctica

The movements of gentoo penguins (Pygoscelis papua) in Antarctica were studied by equipping a total of 37 birds captured at Ardley Island, South Shetlands between December 1991 and May 1996 with position-determining devices. Information on area usage was derived from 20 of these devices and covered the incubation period (N = 3 birds), the chick-rearing period (N = 14 birds) and the over-wintering period (N = 3 birds). During incubation birds only ventured further than 50 km from the colony 20% of the time and no individual ranged further than 200 km from the colony. In contrast, no individuals attending chicks ranged further than 16 km from the colony. During winter the maximum distance ranged from the colony was 268 km. Mean distances between the birds and the colony were 80, 81 and 127 km. Individual birds tended to associate with one spot, making short (10 day) forays away before returning to nodal areas. The ranging capacity of gentoo penguins appears considerably less than that of sympatric congeners and may reflect the ability of gentoo penguins to dive deeper and thus exploit prey not accessible to congeners.

Diet of Westland Petrels Procellaria westlandica: the Importance of Fisheries Waste During Chick-rearing

SummaryThe diet of the Westland Petrel Procellaria westlandica was studied during the chick-rearing period (August—October) from 1993–96. Fish occurred in 92% of samples and formed 78.8 ± 6.5% by weight of the solid food brought back to the colony. Cephalopods were found in 32% of samples and contributed 18.7 ± 6.2% of solid food by weight. Crustacea occurred in only 4% of samples and contributed only 2.4 ± 2.4% of solid food by weight. During the part of the chick-rearing period in which the Hoki Macruronus novaezelandiae fishery was operating (August to mid-September), fisheries waste accounted for 80% of the fish found in samples and formed around 63% of the total diet at that time. After the Hoki season, fisheries waste accounted for only 31% of the fish found in samples, therefore contributing only around 25% of the total diet as birds switched to capturing more natural prey, or scavenged a wider variety of fish species, presumably from smaller, inshore fishing vessels.

The Diet of the Antarctic Shag during Summer at Nelson Island, Antarctica

Analysis of 139 stomach contents of the Antarctic Shag (Phalacrocorax brans-fieldensis) collected at Nelson Island, Antarctica, showed that fish were the main component in the diet, followed by octopods, gammarids, euphausiids, and polychaetes. The fish No-tothenia coriiceps predominated in frequency (56%) and in mass (49%), whereas Harpagifer antarcticus was the most important by number (58%). The sizes of N. coriiceps and H. antarcticus taken by males were significantly larger than those caught by females. This dietary difference is probably due to differential prey selection related to shags' sexual dimorphism, temporal prey availability, and/or different foraging depths/areas. Observations at nests showed that females mainly foraged in the morning, whereas males foraged in the evening. No significant differences were observed between the number of daily foraging trips made by males and females, averaging 1.7 during incubation, 2.0 in early chick-rearing, and 4.6 during the late chick-rearing period. The estimated daily food intakes were 321, 315, and 758 g for females, and 421, 582, and 1,288 g for males during incubation, early and late chick-rearing, respectively.

Factors Affecting Parental Behavior in Semipalmated Plovers

We studied Semipalmated Plovers (Charadrius semipalmatus) during two field seasons in Churchill, Manitoba, to examine the contribution of males and females to parental care during incubation and chick rearing, and to test the hypothesis that birds nesting in habitats with higher visibility and more food (i.e. coastal habitats) tend chicks less closely than birds nesting in habitats with lower visibility and less food (i.e. inland habitats). Males at the coast flew and vocalized more than females during the chick-rearing period, and, in both areas, incubated during the darkest hours (2400 to 0220), whereas females incubated from 0220 to 0530. Incubation shifts were longer at night than during the day but did not differ between sexes or habitats. Incubation by males during the darkest hours may allow females to feed when invertebrates are most active, and may be a mechanism by which fe­ males obtain a better energy balance. Coastal habitats contained more food than inland habitats and more potential predators of both chicks and adults. During incubation, parents in coastal habitats exhibited fewer vigilant behaviors than parents in inland habitats, although the overall time budgets for the most common behaviors did not differ between habitats. Parent-chick distances did not differ between coastal and inland habitats, although as chicks became older, they foraged farther from their parents and were brooded less frequently. The apparent response of adults to predators did not differ between the two habitats. The time that parents spent brooding chicks was negatively correlated with ambient temperatures but was not affected by habitat.

Use of at-sea distribution data to derive potential foraging ranges of macaroni penguins during the breeding season

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 169:263-275 (1998) - doi:10.3354/meps169263 Use of at-sea distribution data to derive potential foraging ranges of macaroni penguins during the breeding season P. N. Trathan*, E. J. Murphy, J. P. Croxall, I. Everson British Antarctic Survey, Natural Environment Research Council, High Cross, Madingley Road, Cambridge CB3 0ET, United Kingdom *E-mail: p.trathan@bas.ac.uk ABSTRACT: Macaroni penguins are the main avian consumer of Antarctic krill in the vicinity of South Georgia. The largest breeding colonies occur on small offshore islands to the northwest of the main island. To delimit the foraging range of penguins from these colonies during the chick-rearing period, we used a series of ship-based survey transects to estimate their distribution and abundance. The survey transects were positioned so as to radiate from a point close to those islands with the largest colonies. Spatial and temporal variations within the data are examined. Penguins were mostly over the continental shelf in water less than 350 m depth and with more than 70% of birds at distances less than 40 km from the main breeding site. To model the observed distribution of penguins, a theoretical at-sea distribution is developed together with a 'potential foraging footprint'. The results are compared with those from previous models based solely on the use of foraging trip duration and at-sea activity budgets. The foraging 'footprint' is probably the best basis currently available for assessing the nature of interactions between macaroni penguins and the commercial fisheries for krill. KEY WORDS: Macaroni penguin · Foraging · At-sea · Colony counts · Eudyptes chrysolophus Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 169. Publication date: August 06, 1998 Print ISSN:0171-8630; Online ISSN:1616-1599 Copyright © 1998 Inter-Research.

Diet of the brown skua Catharacta skua lönnbergi on the Kerguelen archipelago: comparisons between techniques and between islands

The diet of the brown skua Catharacta skua lonnbergi was studied on the Kerguelen archipelago, during the chick-rearing period, over four breeding seasons (1987/1988, 1990/1991, 1992/1993 and 1993/1994). Prey remains and regurgitated pellets left by the breeding pairs were analysed and compared between two nearby and similar islands that mainly differ according to the presence or absence of the rabbit, since its eradication from one of them in 1992. Proportions of prey in diets varied between sampling methods (remains/ pellets), localities, years, breeding territories, breeding pairs and non-breeding individuals. The brown skua preyed upon few species of burrowing petrels and mainly on the blue petrel. Rabbits were exploited secondarily although they apparently reduced the predation pressure on the blue petrel. The eradication of rabbits from one of the islands, during a restoration programme, has not basically changed the trophic interactions between brown skuas and petrels.

How important are pelagic preys for the kelp gull during chick-rearing at the South Shetland Islands?

An analysis of pellets regurgitated indicated adult kelp gulls (Larus dominicanus) on the South Shetland Islands consumed predominantly intertidal prey, whereas previous studies at Antarctic Peninsula sites have reported kelp gulls consuming predominantly pelagic species. The pellets collected at Nelson Island during the chick-rearing period indicated that the limpet Nacella concinna was their most frequent prey, followed by carrion, gammariids, snails and krill. Fish were scarcely represented. Also, regurgitated stomach contents of chicks showed that limpets and carrion were the most frequent food items, accounting for 70% of the mass. However, gammariids were particularly important by number. Significant differences were observed in the overall comparison of the diet as reflected by the two sampling methods. In general, the importance of pelagic prey was negligible when compared to intertidal or scavenged prey. Our results differ greatly from those reported for the Antarctic Peninsula, where chicks were almost exclusively fed with the pelagic fish Pleuragramma antarcticum. These differences could be related to the abundance of pelagic resources in southernmost latitudes, and/or to the presence of more extensive intertidal foraging areas at the South Shetland Islands.

Diving behaviour of the grey-headed albatross

Foraging grey-headed albatrosses spent 86% of the night but only 20% of the day sitting on the sea; most diving activity occurred during daylight. During the broad-guard period of nesting, peaks of diving activity occurred at midday and dusk. During the subsequent chick-rearing period, however, diving was mainly at dawn and dusk. Of 485 dives measured, the depth averaged 0.74 m, with maximum depth at 6.5 m. On average grey-headed albatrosses dived 24 times during a five day foraging trip. Dive depths increased towards midday, probably as a function of the birds' visual acuity rather than due to vertical migration of their prey. We estimate that grey-headed albatrosses may obtain 30–45% of their daily food requirements by diving.

Past and present status and conservation of the seabirds breeding in the Azores Archipelago

The breeding seabirds of the Azores comprise five species of Procellariiformes, four Charadriiformes and one Pelecaniform. This paper reviews their past and present status, ecology and conservation. Historical population trends inferred from 16th and 17th century chronicles indicate dramatic declines for most species. While the main islands were important breeding places in the past, most seabird populations are now restricted to small islets. Intra- and inter-specific competition for nest sites is noteworthy among burrowing Procellariiformes and shortage of optimal breeding habitat seems important in limiting their populations. The chick-rearing periods of Procellariiformes with similar ecological niche do not overlap, suggesting that segregation related to partitioning of food resources or breeding habitat may be operating. Current threats to the Azores seabirds are diverse and may differentially affect the various species. They range from predation by introduced mammals, human disturbance and exploitation, habitat loss due to invasive alien plants and overgrazing by rabbits, and, potentially, competition with fisheries. Although the importance of the Azores seabird fauna was recognised in recent inventories, accurate population estimates are lacking and many potential breeding areas need surveying. For effective conservation much direct action is needed, including management plans for virtually all sites and wardening at the most important sites.

Geomagnetic map used for long-distance navigation?

We used stable isotopes (δ15N and δ13C) and compared prey provided to chicks by each sex to evaluate seasonal and sex-specific diets in Rhinoceros Auklets (Cerorhinca monocerata) in the central California Current system during 2012–2013. Mixing models indicated northern anchovy (Engraulis mordax) were important prey for adults during fall/winter and juvenile rockfishes (Sebastes spp.) were important prey during incubation both years. Adult trophic level increased between incubation and chick-rearing periods in both years. During 2012, δ15N and δ13C of chick-rearing males and females differed significantly; mixing models indicated that females ate more Pacific saury (Cololabis saira) and less market squid (Doryteuthis opalescens) than males. Likewise, females delivered significantly more Pacific saury and less market squid to chicks than males during 2012. Chick growth (g d− 1) and chick survival to fledging were significantly lower during 2012 than 2013, likely because chicks were fed lesser quality prey or fed less frequently in 2012. Lesser body mass of females during incubation in 2012 indicated sex-specific diet differences may have been related to female energetic constraints. The observed variability in Rhinoceros Auklet diet underscores the importance of managing multiple prey populations in this system so that generalist predators have sufficient resources through changing conditions.

Diving Ability of Blue Petrels and Thin-Billed Prions

Capillary depth recorders (Burger and Wilson 1988) are useful tools for studying the foraging ecology of seabirds, and have been used successfully on penguins, alcids, shags and gannets (Burger 1991, Wanless et al. 1991, Adams and Walter 1993, Croxall et al. 1993). Recent studies of Procellariiformes have revealed that diving petrels (Pelecanoides georgicus and P. urinatrix) are able to dive routinely down to 25-40 m (Prince and Jones 1992, Chastel 1994). Furthermore, investigations on albatrosses (Prince et al. 1994), and on the White-chinned Petrel Procellaria aequinoctialis (Huin 1994), have shown that these seabirds can reach a depth of several meters, giving a new insight on the foraging techniques of albatrosses and petrels, which are generally regarded as surface-seizers (Harper 1987, Prince and Morgan 1987). The Blue Petrel Halobaena caerulea and the Thinbilled Prion Pachyptila belcheri are small burrow-nesting petrels (190 and 150 g, respectively). At Kerguelen Islands these two seabirds breed in very large numbers (up to 1 million pairs, Weimerskirch et al. 1989); the prions particularly are believed to have a significant impact on subantarctic resources (Ridoux 1994). During the chick-rearing period (50 days, Weimerskirch et al. 1994), both species alternate long and short foraging trips over pelagic and neritic waters (Weimerskirch et al. 1994) and prey mainly on small crustaceans (Harper 1972, Prince 1980, Ridoux 1994), principally by surface-seizing (Harper 1987, Prince and Morgan 1987). This paper reports the first study on maximum dive depths attained by Blue Petrels and Thin-billed Prions, during the chick-rearing period at Kerguelen Islands.

Regulation of Food Provisioning in the Antarctic Petrel Thalassoica antarctica

Life-history theory predicts that individual birds should invest in reproduction according to their current body condition and the future prospects for survival and reproduction. Thus, it could be expected that current adult body condition should significantly influence food provisioning rates, food loads and concurrent chick growth in the Antarctic petrel. In order to study the significance of parental body condition I correlated meal sizes, feeding frequencies and chick growth with the body condition of the parents. There was a strong correlation between the average meal size delivered to a chick and its growth rate. Adult body condition at the time of hatching was strongly correlated with the average size of meals delivered to individual chicks. Male and female body condition at the time of hatching and average body condition of the pair at the first incubation shift and at hatching significantly influenced the body mass of the chick on day 30. Male body condition and the average body condition of the pair correlated significantly with the growth rate of the chick. The difference in body mass at the age of 30 days of chicks from parents with good body condition compared with chicks from parents with poorer body condition was nearly double that expected. The results strongly suggest that the effort spent during the chick-rearing period, and thus reproductive success, is regulated by the body condition of the parents.

Levels and congener pattern of polychlorinated biphenyls in kittiwakes ( Rissa tridactyla), in relation to mobilization of body-lipids associated with reproduction

Three groups of female kittiwakes ( Rissa tridactyla) were collected in a North-Norwegian colony: (i) before breeding; (ii) immediately after egg-laying; and (iii) late in the chick-rearing period. Concentrations of 21 selected individual polychlorinated biphenyls (PCBs) were determined in liver, brain and fat tissues by capillary gaschromatography (GC-ECD). This was done in order to investigate how the mobilization of lipids associated with breeding influences concentrations and compositions of PCBs in these tissues. The results indicate an average decrease in body mass from pre-breeding to late chick-rearing of almost 20%. During this period, the mean concentration of PCBs in brain tissue approximately quadruples. This increase can be attributed to the redistribution of PCBs from utilized depot fat to metabolizing organs. A strong negative correlation was found between body mass and lipid weight PCB-concentrations in all three tissues. The relative amounts of different PCB-congeners were quite similar in different tissues, and showed only minor changes during the breeding period.

Factors Affecting Daily Activity Budgets of South Georgian Shags during Chick Rearing at Bird Island, South Georgia

Radio telemetry was used to record daily activity budgets of 26 South Georgian Shags (Phalacrocorax georgianus) during the chick-rearing period at Bird Island, South Georgia. There was a significant sex difference in the timing of feeding, with the female making the first trip of the day in 93% of pairs (n = 15). On average, each shag made 2.3 trips/day and was absent for a total of 6.22 hr/day. The majority of time away from the colony was spent diving (86.7%), but long recovery periods on the surface between dives and time needed to travel to the seabed resulted in only 1.06 hr/day being potentially available for prey capture. Given that these activity data were collected during a season when feeding conditions were favorable, breeding shags at Bird Island appear to have little capacity to increase the time available for prey capture. We speculate that the population may be extremely sensitive to changes in food availability. Males spent more time flying and on the sea than did females. On average, birds with broods of two or three chicks spent more time diving (6.42 hr/day) than those with broods of one (4.74 hr/day) but there was no tendency for the amount of time spent diving to increase with chick age. Although South Georgian Shags exhibited the same sexually distinct foraging patterns as Antarctic Shags P. bransfieldensis at a colony on the Antarctic Peninsula, their activity budgets differed radically, with shags at Bird Island spending a much greater percentage of their time away diving (86.7% compared with 8.4%)

Adoption of Chicks among Thick-Billed Murres

Thick-billed Murres (Uria lomvia) breed in dense aggregations on cliff 'edges. Like Common Murres (U. aalge), they build no nests, the single egg being laid on bare rock. Breeding murres of both species rarely leave their egg or chick unattended, but they may do so in the event of attacks by predators, in response to disturbances (e.g. nearby rockfalls; Gaston and Nettleship 1981), under conditions of extreme food stress (Birkhead and Nettleship 1984), or occasionally in response to severe attacks by mosquitos, or heat stress (A.J.G. pers. obs.). During periods of desertion, eggs may roll away from the site and chicks may run up to several meters from the site in order to seek shelter in crevices, or to avoid predators. However, parents recognize their own egg by its color and markings (Tschanz 1959, Gaston et al. 1993), and their chick by its call (Tschanz 1959). The chicks also are capable of recognizing the calls of their parents and actively seek to return to them once they return to the site. When their own egg is lost, murres sometimes incubate the egg of another bird, either appropriating one left unattended, or even stealing one from under an incubating neighbor. Chicks hatched from such appropriated eggs are reared in normal fashion. When foreign eggs have rolled from adjacent sites, birds may attempt to incubate more than one egg, but in such cases no more than one hatches (Gaston et al. 1993). Tschanz (1959, 1979) and Birkhead and Nettleship (1984) observed Common Murres protecting foreign chicks that were temporarily deserted by their parents during a period of food shortage. Wanless and Harris (1985) reported two cases where neighbors helped to rear chicks that also were fed by their own parents. None of these observations involved complete fostering. However, Perry (1940) described an apparent adoption of a neighbor's chick by a Common Murre pair. In this note, we describe four cases in which Thick-billed Murre chicks were adopted and reared by foster parents. Three cases involved natural events, while the fourth involved a chick displaced during banding activities. All observations were made at Coats Island, Northwest Territories, Canada in 1993 and 1994. Observations were made daily in both years throughout the chick-rearing period. Methods used were the same as those described by Gaston et al. (1993). Our observations caused no disturbance to breeding birds, so they cannot account for the three apparently natural adoptions. Case 1.-A five-day-old chick was present at site D154 on 25 July 1993, but was missing on 26 July, when a chick of similar age was being brooded by a bird at site D54, about 1.5 m directly below D154. The pair at D54 already had a chick that was one to four days old at that time. The ledge that they occupied supported two other pairs, one of which was incubating an egg that was eventually deserted after it failed to hatch within the normal incubation period. The other was occupied by a pair that was never known to have laid an egg. Both members of the pair at D54 were banded as breeders at the same site in 1986 and had definitely bred at the site annually since 1988. They brooded both chicks continuously throughout the rearing period, one chick usually being under a wing and the other under the breast. Fighting between the chicks was not observed. The pair at D154, also both uniquely banded, remained at their site and made no further breeding efforts. They were never seen to land anywhere except at their own site. Feeding was observed at D54 twice, but we did not see which chick was fed. The plumage development of both chicks was normal. The larger chick (presumably the older, adopted chick) departed from the site at 2023 EST on 14 August, making a successful glide to the sea. Both foster parents were present when it left, but neither interacted with it as it prepared to depart, or accompanied it (for descriptions of adult and chick behavior at departure, see Tschanz 1959, Gaston and Nettleship 1981). Unless it was adopted at sea (some observations suggest that this may occur; G. Gilchrist unpubl. data), the chick would have perished because chicks are fed by the male parent for at least a month after leaving the colony (Scott 1990). The smaller chick left at 2153 the next night, accompanied by both parents, although, as is normal in Thick-billed Murres (Gaston and Nettleship 1981), the female returned to the breeding site within 10 min and continued to occupy it for several days thereafter. Case 2.-At site P23, the egg disappeared on 25 July

The distribution of Manx ShearwatersPuffinus puffinusin north-west European waters

Seabirds in north-west European waters were surveyed offshore throughout the year from 1979 to 1993. During the breeding season the distribution of Manx Shearwaters centred around the main colonies of Rhum, Skomer and Skokholm. Densities were low in the North Sea, where birds were mainly restricted to waters off the north-east coasts of England and Scotland, in particular the Moray Firth, the Firth of Forth and Flamborough Head. Manx Shearwaters can forage at long distances from the colonies, but highest densities were observed in the Irish Sea, south-west Wales, south-west Ireland and the inshore waters of West Scotland during the chick-rearing period when parent birds visit the colony more frequently. The area of the Irish Sea front was important, particularly in the autumn, and feeding occurred here in preference to other areas of the Irish Sea. From November to February Manx Shearwaters were virtually absent from north-west European waters.

INTRASPECIFIC VARIATION IN EGG SIZE AND EGG COMPOSITION IN BIRDS: EFFECTS ON OFFSPRING FITNESS

1. There is little unequivocal evidence to date in support of a positive relationship between egg size and offspring fitness in birds. Although 40 studies (of 34 species) have considered the effect of variation in egg size on chick growth and/or survival up to fledgling only 12 studies have controlled for other characters potentially correlated both with egg size and offspring fitness. Of these only two have reported a significant residual effect of egg size on chick growth (in the roseate tern and European blackbird) and three a residual effect on chick survival (all in seabirds: common tern, lesser black-backed gull and kittiwake). 2. More consistent evidence exists, though from fewer studies, for a positive relationship between egg size and offspring fitness early in the chick-rearing period; chick growth and chick survival being dependent on egg size in 8 of 10 studies and 4 of 5 studies respectively. It is suggested that the most important effect of variation in egg size might be in determining the probability of offspring survival in the first few days after hatching. 3. Egg size explains on average 66% of the variation in chick mass at hatching (n = 35 studies) but only 30% of the variation in chick body size (n = 18). When effects of hatching body size are controlled for chick mass remains significantly correlated with egg size, though the reverse is not true. This supports the hypothesis that large eggs give rise to heavier chicks at hatching, i.e., chicks with more nutrient (yolk) reserves, rather than structurally larger chicks. 4. Egg composition increased isometrically with increasing egg size in about half the studies so far reported (n equals approximately 20). However, in seabirds, and some passerines, larger eggs contain disproportionately more albumen, whilst in some waterfowl percentage yolk content increases with increasing egg size. Changes in albumen content largely reflect variation in the water content of eggs, but changes in yolk content involve variation in lipid content, and therefore in egg 'quality.' The adaptive significance of variation in egg composition is considered; females may adjust egg composition facultatively to maximise the benefits to their offspring of increased reproductive investment. 5. Considerations for future research are discussed with particular emphasis on experimental studies and the application of new techniques.

The diet of ShagsPhalacrocorax aristotelisduring the chick-rearing period assessed by three methods

This paper describes a study of the diet of Shags using regurgitations by chicks, stomach contents and pellets collected concurrently. Sandeels predominated in all collections. Non- and failed breeders took a wider food spectrum than did chicks. Although adults fed their chicks almost entirely on sandeels, they themselves ate some fish from other fish families and probably digested these before they returned to the colony. Pellets are easy to collect and are useful to detect gross changes in diet of full-grown, but possibly non-breeding, Shags between years or colonies. Otoliths recovered from pellets cannot be used for age determination or back-calculations of size of sandeels eaten by Shags. Regurgitations can be used to describe the diet of chicks. There is no easy way to determine the diet of adults feeding chicks.