Chicks In Broods Research Articles

Hatching order and size-dependent mortality in relation to brood sex ratio composition in chinstrap penguins

The differential environmental sensitivity of the sexes has strong implications in the evolutionary history of species as it can alter sexual size dimorphism, population sex ratios, and the faculty of parents to manipulate offspring sex in relation to environmental conditions. We studied sexual differences in hatching patterns and evaluated sex- and size-related mortality in relation to hatching order and brood sex ratios in the chinstrap penguin Pygoscelis antarctica, a moderately size-dimorphic species, with a modal clutch size of 2 eggs. We found that male, second-hatched, and large eggs showed shorter hatching periods than female, first-hatched, and small eggs. We also found a male-biased mortality of nestlings in the colony. However, male mortality patterns differed depending on the brood sex ratio composition. Mortality of male chicks in all-male broods was higher than in mixed broods and higher than female mortality in all-female broods. Contrary, females from mixed brood showed higher mortality than their male nest mates and higher too than females in all-female broods. Second-hatched chicks also suffered from higher mortality than first-hatched chicks. Our results indicate that both the superior competitive capacity and the higher energy demand of the larger sex constitute 2 causal factors explaining patterns of sex-biased mortality. Both factors occur in the same species and in different situations of sibling competition shaped by brood sex ratio composition. This study constitutes a good example of how patterns of sex-related mortality can vary depending on nest environmental circumstances. Furthermore, our study suggests that hatching period can be a mechanism underlying sexual differences in the embryonic period of birds.

Parental roles of male and female thick-billed murres and razorbills at the Gannet Islands, Labrador

We studied female and male parental roles in two sympatric auks, thick-billed murre (Uria lomvia) and razorbill (Alca torda), with initial biparental care at the breeding site and later exclusively paternal care at sea. Our study addressed the following two questions: Why do males accompany chicks to sea?, and How do the sexes allocate parental effort at the breeding site before parental care at sea begins? We tested the hypothesis that males care for chicks at sea because they are in better condition at the time of chick departure as a result of femalebiased parental effort at the breeding site (‘nest’). Breeding success and duration of chickrearing did not differ between the two study years in either species at the Gannet Islands, Labrador. At the breeding colonies, females of both species provided more food (murres: 2.84 ± 0.18 loads day−1; razorbills: 2.02 ± 0.11 loads day−1) to their chicks than males (murres: 2.26±0.12 loads day−1; razorbills: 1.42±0.09 loads day−1), and males spent more time brooding the chicks. These differences were chick-age dependent in both species, with females providing more meals to chicks older than two weeks. Razorbill males spent more time with chicks greater than two weeks old, while murre male’s attentiveness of brooding did not vary with chick age. In both species, males (murres: 3.04 ± 0.3 h day−1; razorbill: 3.30±0.2 h day−1) performed longer foraging trips with meal delivery than females (murres: 1.23 ± 0.4 h/day; razorbill: 2.50 ± 0.4 h day−1). Thick-billed murres showed a consistent diurnal pattern of egg and chick attendance: females were usually found at the breeding site during the day whereas males were found there early in the morning and at night. In contrast, razorbill’s timing of attendance was much more variable and did not differ between sexes. Despite these differences in timing of breeding site attendance between species, males of both species spent twice as much time as females engaged in the defence of the egg or chick at the breeding site, which suggest male-biased capability of protecting the chick at departure. Overall our data indicated different female and male parental roles at the breeding site but not a female-biased allocation of time, energy and risk as predicted. In fact, males seem to provide equal if not more parental effort than females prior to the time of colony departure. We propose that the patterns of parental roles found between sexes is the result of a chain of events favouring male involvement in chick brooding and care at sea.

Brood size and immunity costs in zebra finchesTaeniopygia guttata

Birds rearing experimentally enlarged broods have lower antibody responses to a novel antigen, and we tested three hypotheses that could explain this result. We used zebra finchesTaeniopygia guttatainoculated with sheep red blood cells (SRBC) as a study system, for which this trade‐off was previously demonstrated. 1. Compensatory cellular immunity: The humoral immune response is slow, and removal of SRBC through up‐regulated cellular immunity could pre‐empt an antibody response. However, cellular immune response to PHA decreased with increasing brood size, allowing rejection of this hypothesis. 2. Costs of antibody‐production: Chicks in large broods grow less well, and birds with large broods may allocate resources to chicks instead of antibodies when these are costly. Compared to saline controls, SRBC suppressed metabolic rate in the hours following immunisation, but there was no effect in the following night, or at any time 4 and 8 days later. Fitness costs were measured by repeatedly immunising parents with SRBC while rearing young. Chick growth, parental condition, and subsequent reproduction of the parents were not affected by SRBC. We conclude that the costs of antibody formation cannot explain the trade‐off between brood size and antibody responsiveness. 3. Costs of immune system maintenance: Maintaining a system enabling antibody‐formation may be very costly, and birds rearing large broods may have down‐regulated this system. Based on this hypothesis we predicted that antibody formation would still be reduced in parents rearing large broods when immunised after rearing the chicks. Our results confirmed this prediction, and we suggest that birds rearing large broods have lower antibody responses because they economised on the maintenance costs of the immune system.

Evidence of re‐nesting after brood loss in Red Grouse Lagopus lagopus scoticus

The Red Grouse Lagopus lagopus scoticus is a single-brooded species that can re-lay if a clutch is lost during the nesting period (Cramp & Simmons 1980). However, there is no reported evidence regarding second clutches being attempted after a brood of young chicks is lost. Indeed, there is only one record of re-nesting after brood loss in Galliformes and this refers to the Ring-necked Pheasant Phasianus colchicus (Dumke & Pils 1979). In that study four ‘wild’ Pheasant hens in Wisconsin were recorded as having re-nested after brood loss. However, doubts about the short time intervals between suspected re-laying, incubation and hatching noted for at least two of the birds suggest that nest appropriation played some part in the result (Dumke & Pils 1979). During the summer of 2003, we monitored a number of radiotagged hen Red Grouse on a heather Calluna vulgaris moor managed for Red Grouse in the Scottish central highlands. Without disturbing the hen, we used radio-telemetry on alternate days through May to monitor whether the hen was incubating and thus determine hatch date. After hatch, we located hens by radiotelemetry and used trained pointing dogs to find chicks on days 5, 10 and 15 after hatching. Thirty-three hens successfully hatched chicks from their first nesting attempt. Of these, 15 lost their entire brood in the first 15 days after hatching. However, we found that two of these hens (A and B) produced a second brood after the loss, for unknown reasons, of their first brood between days 5 and 10. The presence of a second brood was established on the 50th day after each first clutch had hatched, as hens were located at this time to determine survival rates. Hens A and B were found to have chicks judged, from the juvenile primaries, to be under 12 days of age (Parr 1975). In comparison with other chicks of known ages, they were estimated to be 7–10 days of age for the four chicks with Hen A and 10–12 days for the five chicks with Hen B. We estimate that Hen A would have re-laid between 4 and 9 days after brood loss and Hen B between 3 and 8 days after brood loss. These second broods would have hatched in mid-June 2–3 weeks after the main hatching period. Hence Red Grouse can, if rarely, re-lay and produce second broods after losing the first. Although we cannot exclude nest appropriation, we think that the time between brood loss and re-laying, along with the well-documented parental abilities of Red Grouse, support our conclusion. We thank Phones and Ralia estates for access, David Howarth, Nadine Clark and Scott Newey for help during the field season, Kate Graham and two anonymous referees for comments on the manuscript, and the Game Conservancy Scottish Research Trust for funding.

Hormonal correlates of siblicide in Nazca boobies: support for the Challenge Hypothesis

The androgen hormone testosterone (T) mediates vertebrate aggression in many contexts and according to the Challenge Hypothesis is up-regulated during social challenges. While originally applied to challenges experienced by breeding adults, we show for the first time that T is similarly up-regulated during deadly sibling aggression in young birds. When two nestling Nazca boobies hatch, one—usually the older chick—virtually always kills the other chick by pushing it from the nest. We compared concentrations of T, dehydroepiandrosterone (DHEA; a precursor of T), and corticosterone (Cort; a stress hormone) of chicks at various stages. T was elevated during fights in both chicks in two-chick broods, but not before and after fights, and not in chicks lacking a nest mate. DHEA was elevated 1 day after hatching and declined with age but appeared not to vary in concert with aggression. Cort did not vary across fighting and nonfighting periods. In conjunction with an earlier study [Tarlow, E.M., Wikelski, M., Anderson, D.J., 2001. Hormonal correlates of siblicide in Galápagos Nazca boobies. Horm. Behav. 40:14–20], these results indicate that T is temporarily up-regulated around the time of fights, as predicted by the Challenge Hypothesis. Our data suggest a general role for T during challenges at any time in life, not just during breeding.

Sequential Polyandry in Piping Plover, <em>Charadrius melodus</em>, Nesting in Eastern Canada

On Cape Sable Island, Nova Scotia, we confirmed that a banded female Piping Plover (Charadrius melodus melodus) produced two broods of chicks during the 2000 nesting season, the second on a beach approximately 2 km from the first. The female abandoned her second brood two days after hatching, leaving the male to complete brood rearing.

Long days, long trips: foraging ecology of female rockhopper penguins Eudyptes chrysocome chrysocome at Tierra del Fuego

In rockhopper penguins Eudyptes chrysocome, the relationship between foraging effort and the daylight period is unclear. We studied the foraging ecology of female southern rockhoppers that were brooding chicks at Bahia Franklin (Staten Island) in December 2000. We compare our data with data presented for other subspecies and locations, analyzing the features of their foraging ecol- ogy and its relationship with the daylight period around Staten Island, the population size of differ- ent breeding locations and the marine environment. Southern rockhopper penguins performed longer trips (about 30 and 60% longer for daily and overnight trips respectively) and between 5 and 7 more overnight trips (53%) than the northern and eastern subspecies. Mean dive depth and dive duration were 28.9 ± 24.6 m and 79 ± 30 s respectively. The diving rate (30.4 ± 5.0 dives h -1 ), and the proportion of trip duration underwater (66.2 ± 5.9%) confirmed the high foraging effort of rockhop- per penguins. During the study period foraging trip duration increased, but dive parameters did not vary. Penguins traveled as much as 20 km to their foraging waters, either in shelf waters and/or in waters of a close shelf-break and slope. The diet was dominated in numbers by euphausiids, amphipods, cephalopods, fish larvae and juveniles, all prey species commonly found in Subantarctic waters. The long trips could be explained by the long twilight period and by diel vertical migration of prey, confirming the phenotypic plasticity of penguins in response to different marine environments. The extended foraging trip duration may contribute to sustaining the high level of the breeding population (167 000 breeding pairs) at Bahia Franklin, and account for differences in the recent his- tory of different breeding colonies in the SW Atlantic Ocean.

Foraging strategy of a top predator in tropical waters: great frigatebirds in the Mozambique Channel

Although oceanic tropical waters occupy almost 50% of the total area of pelagic oceans, knowledge of the foraging ecology of top predators in these low productivity waters is limitied. This is particularly the case for tropical seabirds that are believed to rely on scarce and unpredictable resources and have developed specific foraging strategies to exploit these resources. Frigatebirds are tropical seabirds that rely on subsurface predators such as tuna or cetaceans to feed. We studied the foraging strategy at sea of great frigatebirds breeding on Europa Island in the Mozambique Channel using satel- lite transmitters and altimeters. When foraging, birds moved at slow speeds (average 16.4 km h -1 ) and stayed at an average altitude of 180 m, continuously climbing and descending. During climbs, they reached high altitudes (maximum 2867 m) and during descent rarely came close to the surface to feed. Birds came to the surface on average 6.2 times d -1 . Feeding opportunities occurred only during the day, peaking early in the morning and late in the afternoon. Frigatebirds foraged over extensive distances, up to 612 km from the island, usually during the incubation or post-breeding periods, concentrating their effort in the western oceanic waters of the channel where overall productivity, although low, was still higher than in the eastern part of the channel. The higher productivity in the western waters is due to the presence of a persistent field of mesoscale anticyclonic gyres. Birds tended to avoid the centre of cold eddies and remained at the edge of eddies. When brooding chicks, birds foraged closer to the island, at an average distance of 94 km, mainly in the northwest of the island, in the vicinity of shallow waters of the Bassas da India Bank. During both long and short trips, birds did not return to the same area. Diet was composed essentially of flying-fish and Ommastrephid squids. The results of the study indicate that the strategy of frigatebirds is based on wide ranging foraging directed toward scarce prey patches that are encountered irregularly, and are not predictable in exact location at a coarse scale. At a mesoscale level, birds appear to favour large areas with slightly enhanced productivity such as a zone of strong eddies. Since they feed in close association with subsurface predators, mainly tuna in our area, it can be predicted that large predators such as seabirds or tuna are spread over extensive areas and have an unpredictable localisation at a coarse scale, but have some specific preferences on a regional scale.

In-depth studies of Magellanic penguin ( Spheniscus magellanicus ) foraging: can we estimate prey consumption by perturbations in the dive profile?

A new concept based on analysis of dive depth data was developed to help estimate prey consumption in ten free-ranging Magellanic penguins (Spheniscus magellanicus) that were brooding chicks. By simultaneously analysing the undulations in the dive depth profile (measured by time-depth recorders, TDRs) and beak opening (obtained from the recently developed intra-mandibular angle sensors, IMASEN), it was possible to determine the proportions of the undulations in the dive profile that resulted (or not) in prey capture. This methodology allowed the number of prey consumed to be estimated with a mean error of 10±6% using TDR data alone. If the mean mass of prey is known, then the overall mass of prey consumed per unit time can be determined. Additionally, the method allows estimation of the depth at which prey is taken and thus indicates how penguins exploit the water column. Due to its simplicity, the proposed methodology has applications for other Spheniscus penguin species and should be considered for other marine endotherm divers that show undulations in the dive depth profile.

No evidence for differential maternal allocation to offspring in the house sparrow (Passer domesticus)

We tested the differential maternal allocation hypothesis in a population of house sparrows. We experimentally altered the attractiveness of males by treating them with implants filled with crystalline testosterone (T) or left empty (C). We subsequently monitored maternal investment as a function of male hormonal treatment and the size of the black patch of feathers on the throat (i.e., the badge), a sexually selected trait. The differential allocation hypothesis predicts that females should adjust their investment with respect to the benefits they receive by mating with an attractive male. Given that both circulating levels of T and badge size are condition-dependent traits, we expected that females mated with T males and/or with large-badged males should invest more into current reproduction. Contrary to this prediction, we found no evidence that suggested differential maternal allocation in this population of house sparrows. Female investment in yolk T, yolk mass, clutch size, chick brooding, and feeding was not affected by male hormonal treatment or by male badge size. As expected, T males invested less into chick brooding and feeding. More surprisingly, females did not compensate the reduced paternal contribution to chick feeding. As a consequence, the breeding success of T pairs was largely reduced compared with that of C pairs. The absence of differential allocation in a system in which it could have an adaptive role raises the question about the possible constraints or overriding factors operating on patterns of reproductive investment in this species. .

Influences of sex, sex composition of brood and hatching order on mass growth in common terns Sterna hirundo

We studied sex-dependent mass growth of chicks of the monomorphic common tern Sterna hirundo which fledged at a colony site in Wilhelmshaven, Germany, between 1997 and 1999. Brood size, brood mates' sex and hatching order (a-, b- and c-chicks) were known for many individuals, which were sexed by molecular techniques. Daily growth rates and age of fledging were independent of sex. However, in all years male chicks reached higher peak mass and fledged up to 5.2% heavier than female chicks. Broods with at least two fledglings showed that besides sex, brood size interacting with sex composition affected chick mass. In mixed broods, brothers had higher peak and pre-fledging mass than sisters they were reared with. Especially in the combination a-daughter and b-son the brothers were heavier. Lowest mass was found in broods with three nest mates of the same sex. A detailed study of 24 three-fledgling broods showed that male c-chicks were heavier than their siblings. The results reveal an advantage for chicks in mixed broods, especially for sons, and more especially if the son was a c-chick. Higher mass and possibly dominance of sons in c-position might be related to higher maternal androgen levels, which are known to increase with each egg laid. The results suggest that even in a monomorphic species, sons might be more expensive to rear, and are discussed with respect to sibling competition, parental effort, survival of sons, as well as to fitness benefits favoring parents producing sons.

Sex‐specific patterns in baseline corticosterone and body condition changes in breeding Red‐footed Boobies Sula sula

Plasma levels of corticosterone often mirror changes in body condition and parental effort. In seabirds, the brooding of young chicks is often paralleled by a marked decline in adult body condition. This may reflect the trade‐off between the needs of the chick to be fed regularly and brooded, and that of the adult to spend enough time at sea to restore its body reserves and find food for the chick. In this paper, we describe changes in body condition and baseline corticosterone levels in a tropical seabird, the Red‐footed Booby Sula sula, in which the chick is continuously brooded for 5–6 weeks. Body condition did not decline during the brooding period. Female body condition remained stable throughout breeding whereas male body condition declined significantly during the late chick‐rearing period. Baseline corticosterone levels were low during the prelaying phase, increased significantly during incubation and were highest during the brooding period. Later in the chick‐rearing period, baseline corticosterone levels decreased markedly in females, but stayed elevated in males. There was no correlation between baseline corticosterone and body condition. Because of the chick's slow growth and reduced daily need for food, brooding in Red‐footed Boobies may not require a marked increase in parental effort, and the rise in corticosterone levels is probably more a reflection of slight changes in foraging activity. Red‐footed Booby males are 15% smaller than females and we suggest that the decline in male body condition during the late chick‐rearing period is likely to result from higher energetic flight costs or a lower foraging efficiency imposed by a smaller body size.

Effect of female brooding behaviour on male mate choice in Japanese quail, Coturnix japonica

Brooding behaviour is a likely cue to a female's reproductive status and therefore a potentially important factor in male mate assessment. We induced brooding behaviour in adult female Japanese quail by exposure to foster chicks for five 20-min trials over 3 days. In two experiments, we assessed the influence of this brooding behaviour on male mate choice in Japanese quail using an established mate choice paradigm. In each experiment we gave males a choice between two females presented simultaneously and measured preference by the time spent in proximity to each. In the first experiment, a male's preference for the initially preferred female significantly decreased after he had seen her brooding three chicks. In the control condition, male preference for an initially preferred female remained relatively consistent over consecutive trials if he did not see her brood chicks. These results suggest that females who are brooding chicks are less attractive to male Japanese quail. Further evidence from the second experiment substantiates this finding, and strongly suggests that males are averse to behavioural cues from maternal females, rather than the mere presence of chicks. Copyright 2003 The Association for the Study of Animal Behaviour. Published by Elsevier Science Ltd. All rights reserved.

Which chick is tasty to parasites? The importance of host immunology vs. parasite life history

Summary The Tasty Chick Hypothesis (TCH) proposes that hatching asynchrony evolved as an antiparasite strategy. Hosts would benefit if ectoparasites aggregate more on the offspring that are of lowest reproductive value within a brood, i.e. on the last‐hatched chicks, because offspring reproductive value generally decreases with hatching rank. The poor body condition of the later‐hatched chicks would impair parasite resistance and render them especially attractive to ectoparasites. Thus, the TCH predicts a decline in chick parasite load with hatching order in avian broods. We investigated the main assumption of the TCH that junior chicks are less immunocompetent than their senior siblings. We also examine the prediction of the TCH that junior chicks bear more ectoparasites than their senior siblings. Conform to the assumption of the TCH for hosts, junior chicks in broods of the barn owl (Tyto alba L.) showed a lower humoral immune response than their senior siblings. In contrast, the cell‐mediated immune response of senior chicks in broods of the great tit (Parus major L.) was not significantly greater than that of their junior siblings. In line with the prediction of the TCH for the distribution of parasites among hosts, the fly Carnus haemapterus Nitzsch infested junior chicks in larger numbers than senior chicks in both barn owl and kestrel (Falco tinnunculus L.) broods. In conflict with the TCH, ticks (Ixodes ricinus L.) were distributed randomly with respect to hatching rank in broods of the barn owl and the great tit. Moreover, louse‐flies Crataerina melbae Rondani infested mainly senior chicks instead of junior chicks in the Alpine swift (Apus melba L.). Summarizing, the present descriptive study indicates that the distribution of ectoparasites within‐broods is not generally governed by rank‐related variation in host defence of chicks as initially suggested by the TCH. We argue that specific aspects of the morphology, life history and ecological requirements of various ectoparasite species need more consideration as to explain the dynamics and evolution of host–parasite interactions.

Siblicidal brood reduction in South Polar Skuas

Siblicide in the South Polar Skua (Catharacta maccormicki) was studied at Cape Crozier, Ross Island, Antarctica during the 1993/94 austral summer. Sixty‐six two‐egg nests were monitored, providing 49 two‐chick broods for study. Eighteen pairs of chicks (37% of broods) were raised. Single chicks survived in 27 nests, of which 26 were first chicks. Only three second chicks outlived firsts in the same brood, of which only one survived to at least 20 days. Attacks began within the first days of the second chick hatching. Second chicks were lost or evicted from the nest area on average 3.05 ± 0.5 days (mean ± SE) after hatching. Although first and second chicks had almost identical body masses at hatching (68.3 ± 4.7 g versus 69.9 ± 5.6 g), first chicks weighed 102.3 ± 4.2 g when the second hatched. At the peak of attacks at 48 h after the second hatched, first chicks weighed 146.5 ± 4.7 g on average and seconds only 83.3 ± 1.8 g. Between‐brood differences in mass and age of chicks in different broods had minimal influence on either the intensity of sibling aggression or its outcome. First chick aggression towards the second persisted for at least 3 weeks in broods kept separately in enclosures at the nest. All attacks began near the nest, usually at chick feeding. Parents intervened in a high proportion of attacks, invariably in pecking attacks, but did not halt them in the longer term. Twelve of 26 second chicks survived for a time elsewhere on the territory or were adopted by neighbours after being evicted from the nest area. Brood reduction through siblicide in this species is a two‐phase process: eviction from the nest area, followed by death from predation, exposure or starvation. A review of the literature showed that varying levels of siblicide occur throughout the entire breeding range of the South Polar Skua, and, except for some possible records for the Brown Skua, is uniquely confined to this species within the Stercorariidae. We concluded that brood reduction through siblicide is facultative, its intensity in each population each season determined by local foraging conditions.

Summer diet of king penguins (Aptenodytes patagonicus) at the Falkland Islands, southern Atlantic Ocean

The diet of king penguins (Aptenodytes patagonicus) brooding chicks was investigated during February 2001 at the Falkland Islands, where a small but increasing population is located at the limit of the breeding range of this species. Fish was the most important food source by number (98.0%) and reconstituted mass (97.8%), squids accounting for the remainder. Myctophid fishes represented the main part of the diet (97.7% by number and 96.6% by reconstituted mass), Protomyctophum choriodon being by far the main prey item (84.2% and 88.1%, respectively). Four other myctophids and one squid species each contributed to more than 1% of the diet by number: Krefftichthys anderssoni (4.8%), Electrona carlsbergi (4.6%), Gymnoscopelus nicholsi (2.2%) and Protomyctophum tenisoni (1.8%), together with small juveniles of Gonatus antarcticus (1.8%). Twelve squid species were identified from accumulated lower beaks, including the ommastrephid Martialia hyadesi (48.3% by number), the onychoteuthids Moroteuthis ingens (15.6%), Kondakovia longimana (10.5%) and Moroteuthis knipovitchi (7.3%), and Gonatus antarcticus (9.2%). The stable-carbon and stable-nitrogen isotopic composition of chick food and adult blood differed in a way that suggests that, during the same trip, adult birds fed for themselves in distant foraging grounds, and fed for their chicks on their way back to the colony. The study emphasizes that king penguins are specialist myctophid eaters throughout their breeding range in summer, and highlights the importance of Protomyctophum choriodon as a link between zooplankton and top predators in the pelagic ecosystem of the southwestern Atlantic Ocean.

Seasonal changes in the diving parameters of king penguins ( Aptenodytes patagonicus )

Contrasting conditions at-sea are likely to affect the foraging behaviour of seabirds. However, the effect of season on the dive parameters of penguins is poorly known. We report here on an extensive study of the diving behaviour of king penguins (Aptenodytes patagonicus) over the bird's complete annual cycle at the Crozet Islands. Time-depth recorders were used to record dive duration, bottom duration, post-dive interval, ascent rate and descent rate in breeding adults during different seasons in 1995 and 1996. Seasons included summer (n=6, incubation; n=6, chick brooding), autumn and winter (n=5 and n=3, respectively, chick at the creche stage), and spring (n=4, birds at the post-moult stage). In all seasons dive duration increased with dive depth, but, for a given depth, dives were longer in winter (6.8 min when averaged over the 100–210 m depth layer) than in spring (4.6 min) and summer (4.4 min). The time spent at the bottom of the dives, which probably represents a substantial part of the feeding time, was much longer in winter (2.5 min per dive for dives over the 100–210 m layer) than during other seasons (1.0–1.4 min), i.e. there was a 2.5-fold augmentation for similar diving depths. Ascent and descent rates increased with increasing dive depth, but no difference in the relationships between rates of ascent and descent and dive depth was found among seasons. Furthermore, for all dive depths, ascent and descent rates were independent of the bottom duration. In all seasons post-dive intervals increased with dive duration and with dive depth, but they were longer in spring (2.3 min for dives over the 100–210 m layer) and summer than in autumn and winter (1.6–1.8 min). The diving efficiency decreased with increasing dive depth and was higher in autumn and winter (0.22–0.29) than in summer and spring (0.15–0.18). The large increase in bottom and dive duration from spring to winter is in agreement with the seasonal drop in prey density, with penguins spending more time searching for prey. In contrast, the consistency of the vertical velocity during contrasting conditions at-sea suggests that the transit time to depth is an important component of the foraging behaviour (scanning of the water column) that is independent of the prey availability. The time budget of the penguins during diving in a fluctuating environment appears to vary primarily during the bottom phase of the dives, with bottom duration increasing with diminishing prey supplies, while post-dive intervals shorten in the same time.

Response of pigeon guillemots to variable abundance of high-lipid and low-lipid prey.

Populations of the pigeon guillemot (Cepphus columba) and other piscivores have been in decline for several decades in the Gulf of Alaska and Bering Sea, and a decline in abundance of lipid-rich schooling fishes is hypothesized as the major cause. We tested this hypothesis by studying the breeding biology of pigeon guillemots during 1995-1999 while simultaneously measuring prey abundance with beach seines and bottom trawls. Our study area (Kachemak Bay, Alaska) comprises two oceanographically distinct areas. Populations of a lipid-rich schooling fish, Pacific sand lance (Ammodytes hexapterus), were higher in the warmer Inner Bay than in the colder Outer Bay, and sand lance abundance was higher during warm years. Populations of low-lipid content demersal fishes were similar between areas. Chick survival to age 15days was 47% higher in the Inner Bay (high-lipid diet) than in the Outer Bay (low-lipid diet), and estimated reproductive success (chicks fledged nest-1) was 62% higher in the Inner Bay than in the Outer Bay. Chick provisioning rate (kJ chick-1 h-1) increased with the proportion of sand lance in the diet (r 2=0.21), as did growth rate (g day-1) of younger (beta) chicks in two-chick broods (r 2=0.14). Pigeon guillemots in the Inner Bay switched to demersal prey during years of below-average sand lance abundance, and these birds reacted to 38-fold interannual changes in sand lance abundance with reductions in beta chick growth rates, with no decline in beta chick survival. In contrast, the proportion of nests experiencing brood reduction in the Outer Bay (demersal diet) increased >300% during years of below-average demersal abundance, although demersal fish abundance varied only 4-fold among years. Our results support the hypothesis that recovery of pigeon guillemot populations from the effects of the Exxon Valdez oil spill is limited by availability of lipid-rich prey.

Sex ratio in relation to timing of breeding, and laying sequence in a dimorphic seabird

When the cost of rearing sons and daughters differs and the subsequent survival and reproductive success of one sex is more dependent than the other, on the amount of parental investment, adult females tend to produce more chicks of the more dependent sex if the females are in good condition themselves. One method of varying the total investment in each sex is through modifying the sex ratio of offspring produced. This study shows that in broods of European ShagsPhalacrocorax aristotelis, the sex ratio varied with laying date. Presumably in this species, the lifetime reproductive success of males is more dependent on the level of parental investment. Early breeders are in better condition, the brood sex ratio of early broods was male biased (0.63), while that of late broods was female biased (0.36). The overall difference in sex ratio found between early and late nests could be attributed to manipulation of sex in the first laid egg. In early broods, 77% of the first hatched chicks were male but only 30% of the first hatched chicks in late broods were male. The sex combination of the first two chicks in a brood significantly affected growth as measured by asymptotic mass.

Development of a Solar Supplemented Chick Brooding System in Port Harcourt, Nigeria

The design and development of a solar heated chick brooding facility is presented in which air is used as heat transfer fluid and pebbles as storage medium. With a collector (flat plate) area of 1.35 m2 and rock-bed storage volume of 2m3 the solar heating system was constructed and tested for five stockings in two years along with a conventional system based on kerosene fuel heating. During testing 100 chicks (at day-old) were stocked per system per period. The solar brood system recorded 50% lower chick mortality within the 28-day brooding period as compared to the conventional brooding facility. The average liquid fuel saving was 68% over the non-solar brooder. The solar brood system showed significant (p = 0.05) improvement in all the biological performance parameters (body weight, feathering-out time and feed conversion). The solar brooding facility presented a practical means of utilizing solar energy for chick brooding in place of kerosene in Port Harcourt, Nigeria.