Field experiments on the effect of ticks on breeding success and chick health of cattle egrets

Abstract Two experiments compared broods that were naturally tick-infested with an equal number that were rendered tick-free by application of an acaricide to their nests and of barriers against further infestation. In the first experiment conducted in 1991–92 nestlings in tick-infested broods had up to 159 larval ticks at once and a mean infestation of 23.6 larval ticks per chick per day. The chick's mean tick load was inversely correlated with its longevity. Chicks that survived to at least 18 days post-hatching had significantly lower larval tick loads than those that died by 18 days, excluding the third-hatched chick in each brood whose survival rate was low irrespective of tick-infestation. At 7 days post-hatching, tick-infested chicks had a lower haematocrit and higher polychromasia than tick-free chicks. I infer that blood loss anaemia caused the deaths of tick-infested chicks in their first week. None died in their second week and the demise of those in their third week may have been due to the paralysis manifested prior to their death. I conclude that heavy tick infestation of their chicks reduced the breeding success of the parent egrets below that of the egrets whose chicks were kept free of ticks. In the second experiment in the 1992–93 season the mean level of tick infestation was much lower (5.1 per chick) and these chicks survived equally with tick-free chicks through fledging.     

Comparative reproductive biology of sympatric species: nest and chick survival of American avocets and black‐necked stilts

Identifying differences in reproductive success rates of closely related and sympatrically breeding species can be useful for understanding limitations to population growth. We simultaneously examined the reproductive ecology of American avocets Recurvirostra americana and black‐necked stilts Himantopus mexicanus using 1274 monitored nests and 240 radio‐marked chicks in San Francisco Bay, California. Although there were 1.8 times more avocet nests than stilt nests, stilts nonetheless fledged 3.3 times more chicks. Greater production by stilts than avocets was the result of greater chick survival from hatching to fledging (avocet: 6%; stilt: 40%), and not because of differences in clutch size (avocet: 3.84; stilt: 3.77), nest survival (avocet: 44%; stilt: 35%), or egg hatching success (avocet: 90%; stilt: 92%). We reviewed the literature and confirmed that nest survival and hatching success are generally similar when avocets and stilts breed sympatrically. In addition to species, chick survival was strongly influenced by age, site, and year. In particular, daily survival rates increased rapidly with chick age, with 70% of mortalities occurring ≤ 1 week after hatch. California gulls Larus californicus caused 55% of avocet, but only 15% of stilt, chick deaths. Differential use of micro‐habitats likely reduced stilt chick's vulnerability to gull predation, particularly during the first week after hatch, because stilts nested in vegetation 2.7 times more often than avocets and vegetation height was 65% taller at stilt nests compared with avocet nests. Our results demonstrate that two co‐occurring and closely related species with similar life history strategies can differ markedly in reproductive success, and simultaneous studies of such species can identify differences that limit productivity.     

DOES PREY BIOMASS OR MERCURY EXPOSURE AFFECT LOON CHICK SURVIVAL IN WISCONSIN?

Abstract: Past studies suggest that the productivity of common loons (Gavia immer) is lower on acidic lakes in northern Wisconsin, USA, than on neutral lakes. Two hypotheses have been proposed to explain low chick survival: (1) reduced food consumption related to changes in prey communities on lower pH lakes and (2) high mercury (Hg) exposure on lower pH lakes. To address these hypotheses, we quantified prey and Hg consumption by loon chicks on 51 lakes and survival on 55 lakes ranging in pH from 4.9 to 9.5 in northern Wisconsin in 1995 and 1996. The time adults spent providing prey to chicks was unrelated to lake pH but increased with number of chicks and chick age. The number of prey caught per provisioning time declined as lake pH declined because adults made fewer dives, not because success of prey capture declined. Chicks consumed more insect larvae on acidic lakes and more crayfish (Family Astacidae) on neutral lakes. Biomass consumed ranged from an average 1.99 ± 1.05 (SE) g/hr/chick during the first week of a chick's life to a peak of 7.93 ± 1.93 g/hr/chick during the eighth week. Biomass intake per chick body weight (g/W_g/hr) declined with lake acidity but was not related to chick survival (P = 0.25). Although the Hg concentration in the 3 major prey species was positively related to lake acidity and blood Hg level of chicks at a lake, total Hg consumption (μg/W_g/hr) was highest on moderately acidic lakes rather than on the most acidic lakes. We suggest that loon chick survival in northern Wisconsin lakes is more likely related to prey availability than to Hg exposure. When we removed from our analysis 1 lake where 2 11-day-old chicks were killed by predators, chick survival was negatively related to lake acidity but not to biomass or Hg consumption. We discuss mechanisms of Hg excretion that may allow young chicks to survive on acidic lakes in northern Wisconsin despite high Hg intake.     

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

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

A blood sampling technique for prehatched chicks

ABSTRACT Collecting blood from neonatal or prehatched chicks is sometimes necessary, requiring specialized blood collection techniques and skills. However, such sampling can be difficult and could potentially have adverse effects. I developed a method for collecting blood from chicks still in an egg. The technique involves enlarging the pipping hole, removing the chick's head to take blood from a jugular vein, and returning the chick into its original position in the egg to complete hatching back in the nest. I used this technique on Crested Tern (Thalasseus bergii) chicks (N= 13), with no apparent adverse effects to growth or short‐term survival. The amount of blood extracted (0.1–0.15 ml) was sufficient for a blood smear, hematocrit, and total white blood cell count. This method should be useful for eggs as small as 40 mm in length; eggs smaller than this would likely not be good candidates for this technique because eggshells may be too thin to safely handle. This technique may be useful for investigators studying the immunological and endocrinological transition between embryos and hatchlings.     

Survival of Greater Sage-Grouse Chicks and Broods in the Northern Great Basin

ABSTRACT Reduced annual recruitment because of poor habitat quality has been implicated as one of the causative factors in the range-wide decline of sage-grouse (Centrocercus urophasianus) populations since the 1950s. Because chick and brood survival are directly linked to annual recruitment and may be the primary factors that limit sage-grouse population growth, we estimated 28-day survival rates of radiomarked chicks and broods from 2000 to 2003. We examined relationships between survival and several habitat variables measured at brood sites, including food availability (insects and forbs); horizontal cover of sagebrush, grasses, and forbs; and vertical cover of sagebrush and grass. We monitored 506 radiomarked chicks from 94 broods; chick survival was 0.392 (SE = 0.024). We found evidence that both food and cover variables were positively associated with chick survival, including Lepidoptera availability, slender phlox (Phlox gracilis) frequency, total forb cover, and grass cover. The effect of total grass cover on chick survival was dependent on the proportion of short grass. The hazard of an individual chick's death decreased 8.6% (95% CI = −1.0 to 18.3) for each percentage point increase in total grass cover when the proportion of short grass was >70%. Survival of 83 radiomarked broods was 0.673 (SE = 0.055). Lepidoptera availability and slender phlox frequency were the only habitat variables related to brood survival. Risk of total brood loss decreased by 11.8% (95% CI = 1.2–22.5) for each additional Lepidoptera individual and 2.7% (95% CI = −0.4 to 5.8) for each percentage point increase in the frequency of slender phlox found at brood sites. Model selection results revealed that temporal differences in brood survival were associated with variation in the availability of Lepidoptera and slender phlox. Years with high brood survival corresponded with years of high Lepidoptera availability and high slender phlox frequency. These foods likely provided high-quality nutrition for chicks during early growth and development and enhanced survival. Habitat management that promotes Lepidoptera and slender phlox abundance during May and June (i.e., early brood rearing) should have a positive effect on chick and brood survival in the short term and potentially increase annual recruitment.     

SOME NOTES ON THE CAPE GANNET,Morus capensis

Tarboton, W. R. 1978. Breeding of the Little Banded Goshawk. Ostrich 49:132-143.

The behaviour and vocalizations of a pair of Little Banded Goshawks Accipiter badius during part of their breeding cycle is described. Both sexes built the nest. Two eggs were laid three days apart. The first egg was incubated for 52% of the day, but this increased to 90% when the clutch was complete, of which the female's share was 86% and the male's 4%. The second egg hatched after 29 days, 18 h. The female did not hunt during the incubation or early nestling period and was fed by the male who brought her, on average, 7,0 food objects per day. Lizards formed 73% of the 91 identified prey objects, and small birds, 24%. The female and chick, when 16 days old, were killed by a predator on the nest at night.     

THE BIOLOGY OF ABBOTT'S BOOBY SULA ABBOTTI

766 pairs of Abbott's Boobies Sula abbotti were located on Christmas Island (Indian Ocean), the species' sole breeding ground, and a further 1,058 pairs conservatively estimated to have been missed. To these may be added an arbitrarily chosen figure of two-thirds the number of juveniles which were on the island at the time of the estimate, to represent sub-adults which were probably away at sea, giving a total of 4,200-5,100 individuals. An independent assessment, based on the number of birds flying in to the island, gave a conservative figure of 3,500-4,500 individuals. This represents a very large increase over previous figures which were merely guesses. The distribution of abbotti is mapped in detail. Its correlation with topographical features is described. Nests are usually placed over 70 feet high in dense jungle, above the 500 foot contour. Abbotti is the only sulid that nests relatively solitarily, but even so there may occasionally be three nests in a tree. The most densely populated area held 90 pairs in 876,000 m². The morphology of all ages is described and weights and measurements given. Adult males averaged 1,503 g, females 1,600 g. The species can be sexed on bill colour (pink in female, blue-grey in male) but the juvenile is virtually indistinguishable from the male. Adults apparently suspend moult during breeding and resume it as their offspring approaches independence. The breeding cycle occupies more than 15 months and egg-laying seems restricted to April-July. Breeding must therefore be biennial (or less frequent). The large egg constitutes more than 7% of the female's weight, more than twice as much as in S. bassana (also uniparous) and considerably more than any other sulid. Incubation takes 56 days and incubation stints average about 52 hours. The growth of abbotti is remarkably slow. A comparison is made with that of S. leucogaster on the same island at the same time. The chick is at first fed by complete regurgitation, a habit not shown by any other sulid. Feeds average one per day until the chick is about two months old, and are iess frequent thereafter. Males and females take approximately equal shares in feeding the young. The fledging period is probably 24 weeks or more and is followed by three to four months of post-fledging dependence. Several features of abbotti's breeding biology suggest that it is a distant, oceanic forager. Abbotti is markedly unaggressive, both in rival and pair situations, and the effects of this are traced in the composition of its behaviour repertoire. It is suggested that marked inhibition of close-range aggression has evolved to reduce the likelihood of falling from the tree tops, a particularly potent danger since a grounded abbotti is doomed. Some other aspects of behaviour (e.g. longdistance pair interactions, restrained chick begging) support this interpretation. Abbotti's chief ritualised behaviour pattern is the “ecstatic” meeting ceremony Mutual Wing Waving, which is probably important in maintaining the pair bond, in a species needing such prolonged co-operation in breeding. Wing Waving is also used as a territorial (agonistic) display. Head Jerking, the only other conspicuous ritualised display, is chiefly aggressive but frequently occurs in the pair context. The main elements of abbotti's behaviour are summarised (Table 8) within the sulid framework. The Discussion considers the probable adaptiveness of abbotti's plumage and morphology, the evidence for classing abbotti as a distant forager, its behavioural peculiarities compared with the family norm, and the phylogenetic implications. The future prospects for Sula abbotti are a matter for concern, since Christmas Island is destined for further phosphate mining, involving substantial destruction of cover. It has been suggested that “tree islands” in the key areas would help conserve a significant proportion of the world's abbotti population. It is hoped that a survey of abbotti's numbers and distribution around 1972 will help evaluate the effect which destruction of habitat has already had and provide a basis for estimating future prospects.     

FISHING TECHNIQUES AND FOODS OF THE PIED KINGFISHER ON LAKE VICTORIA IN UGANDA

Douthwaite, R. 3. 1976. Fishing techniques and foods of the Pied Kingfisher on Lake Victoria in Uganda. Ostrich 47: 153–160.

Pied Kingfishers fish by diving from hovering flight or from perches; the choice is influenced by location of the prey and the weather, especially wind speed. 40–50% of the dives into Lake Victoria were successful compared with 11% on the Kazinga Channel, near Lake Edward, but dives were made more frequently in the latter area.

Analysis of pellets from the northern shore of Lake Victoria showed the bulk of the adults' diet was composed of Haplochromis, 55–108 mm (median 80 mm) total length, but that Engraulicypris urgenteus. 40–64 mm (median 52 mm) total length was more important numerically. Flying termites, Macrotermes sp., were occasionally eaten in large numbers.

Size selection related to development determines the proportions of Huplochromis and Engraulicypris in the chick's diet. by comparison with the adult most bone consumed by the chick is digested. Two caged juveniles ate about 34.5 g of fresh fish daily, 45% of their post-absorptive weights. Wild birds may consume even more.     

Cocktail-party effect in king penguin colonies

The king penguin, Aptenodytes patagonicus, breeds without a nest in colonies of several thousands of birds. To be fed, the chick must recognize the parents in a particularly noisy environment using only vocal cues. The call an adult makes when seeking the chick is emitted at a high amplitude level. Nevertheless, it is transmitted in a colonial context involving the noise generated by the colony and the screening effect of the bodies, both factors reducing the signal-to-noise ratio. In addition, the adult call is masked by a background noise with similar amplitude and spectral and temporal characteristics, enhancing the difficulty for the chick in finding its parents. We calculate that the maximum distance from the caller at which its signal can be differentiated from the background noise (signal-to-noise ratio equal to 1) should not exceed 8 to 9 m in a feeding area. But our tests show that, in fact, chicks can discriminate between the parental call and calls from other adults at a greater distance, even when call intensity is well below that of the noise of simultaneous calls produced by other adults. This capacity to perceive and extract the call of the parent from the ambient noise and particularly from the calls of other adults, termed the ''cocktail-party effect'' in speech intelligibility tests, enhances the chick''s ability to find its parents.     

Limited consequences of infestation with a blood‐feeding ectoparasite for the nestlings of two North Pacific seabirds

The seabird tick Ixodes uriae parasitizes over 60 host species in the circumpolar regions of both hemispheres. To assess the impacts of these ticks on the growth and development of nestling seabirds, we used a logistic growth model to interpolate between successive measures of mass (g) and wing chord (mm) for 558 Cassin's auklet Ptychoramphus aleuticus and 344 rhinoceros auklet Cerorhinca monocerata chicks over 11 years (1997–2008, less 2003) on Triangle Island, British Columbia, Canada. From the model, we estimated the asymptotic measure and the age at inflection point for each chick's growth trajectory, and assessed their relationships with tick load relative to other sources of annual and seasonal variation in growth. Most chicks (72.4% of Cassin's auklets, 62.2% of rhinoceros auklets) hosted ≥ 1 ticks, and the median tick load on infested chicks was two in both species. Infestation rates varied by a factor of about two among years (0.42 to 0.87 overall), but were uncorrelated between species and with air temperatures over the preceding winter. The probability of hosting a tick declined strongly with chick age, mainly in the first 20 days after hatching, and to near zero by fledging. Asymptotic weights and/or wing lengths declined with tick load in both species, but at normal loads the reductions were minor relative to those imposed by other factors; only at very high loads, which were rare, were effects likely to be biologically relevant. Tick load and survival to fledging were unrelated in both species. While our study found little influence of ticks, we believe there is need for further study of the relationships between parasites and seabird demography, especially in light of ongoing environmental change.     

Parasitized Salamanders are Inferior Competitors for Territories and Food Resources

Parasites have been shown to impair the behaviour of their hosts, compromising the host's ability to exploit and compete for resources. We conducted two experiments to determine whether infestation with an ectoparasitic mite (Hannemania eltoni) was associated with changes in aggressive and foraging behaviour in the Ozark zigzag salamander, Plethodon angusticlavius. In a first experiment, male salamanders with high parasite loads were less aggressive overall than males with low parasite loads during territorial disputes. In addition, males with high parasite loads were more aggressive toward opponents with high parasite loads (symmetric contests) than toward opponents with low parasite loads (asymmetric contests). In contrast, males with low parasite loads did not adjust their level of aggression according to the parasite load of the opponent. In a second experiment, foraging behaviour of females was tested in response to ‘familiar’ (Drosophila) prey and ‘novel’ (termite) prey. Latency to first capture was significantly longer for parasitized than non‐parasitized females when tested with ‘familiar’ prey, but not for ‘novel’ prey. Our results suggest that parasite‐mediated effects may have profound influences on individual fitness in nature.     

A Cue-Isolation Experiment to Determine if Caspian Tern Parents Learn Their Offspring's Down Color

A ground-nesting gull or tern (Laridae) parent will attack a foreign conspecific chick that is substituted for the parent's chick at about the time the parent's chick is mobile. Presumably, parents discriminate among chicks using some combination of vocal, morphologic, and behavior cues. It is not known which cues are used. Morphologic variation in chicks' down potentially provides discrimination cues in some species of Laridae, such as the Caspian tern (Sterna caspia). To test discrimination based on the down color of chicks, a parent's chick was replaced sequentially with foreign conspecific chicks that were similar and dissimilar to the down color of the parent's chick. This cue-isolation experiment indicated that parents rejected dissimilar chicks more frequently. Thus, parents learn the down color of their chicks and then use this information as a basis for aggressive rejection of foreign chicks. A recognition system based on morphology allows parents to detect and reject foreign chicks with a probability greater than chance.     

Nestling cuckoos,Cuculus canorus,exploit hosts with begging calls that mimic a brood

Nestling cuckoos, Cuculus canorus, eject host eggs or young from the nest and are then raised alone by the hosts. Using reed warblers, Acrocephalus scirpaceus, as hosts, we investigated how the single cuckoo chick can command the same provisioning rate as a whole brood of host young. Large size alone is not sufficient to stimulate adequate provisioning because single blackbird, Turdus merula, or song thrush, T. philomelos, chicks of the same mass as a cuckoo were fed at a lower rate. Our experiments show that the key stimulus is the cuckoo chick''s rapid begging call (''si, si, si, si ...''), which sounds remarkably like a whole brood of host chicks, and which it matched in calling rate. When single blackbird or song thrush chicks were accompanied by loudspeakers that broadcast either cuckoo begging calls or calls of a brood of reed warblers, the hosts increased their provisioning rate to that for a cuckoo chick. We suggest that the cuckoo needs vocal trickery to stimulate adequate care to compensate for the fact that it presents a visual stimulus of just one gape.     

A FIELD STUDY OF THE BEARDED BELLBIRD IN TRINIDAD

The Bearded Bellbird Procnias averano, a medium-sized sexually dimorphic cotingid, was studied for three years in the Northern Range of Trinidad. Its preferred habitat is primary forest at altitudes of 500–1,000 feet and with a rainfall near 100 inches. It is entirely frugivorous, taking mostly drupes. The seeds of the fruits eaten are regurgitated and nearly 2,000 were collected from below the male's calling perch and below nests. Most were from the families Lauraceae and Burseraceae, whose fruits have particularly nutritious pericarps. Adult males own a calling territory from which they call throughout most of the day, and throughout the year except for the period of moult. In each territory there are special saplings where display and mating take place. Only males call; the females are voiceless. The call is loud and far-reaching. In Trinidad P. averano has only two calls, the Venezuelan birds have a third more musical call which appears to have been lost by the Trinidad bellbird during the past 60 years. Both males and females visit the adult male in his calling territory. Here he performs a ritualized display to the visitor, which shows off his black and white plumage, the beard of wattles, and also a bare patch on the thigh. The visit of the female may culminate in mating. All aggressive behaviour observed was between males disputing over calling territories. The female builds the nest, incubates, and rears the chick on her own. The very inconspicious nest is built of twigs that readily interlock. Nearly all the twigs are from two species of tree, and it is suggested that the specialized nest-material may be essential, as the female bellbird builds only with the breast and feet. The clutch consists of a single egg. The incubation and fledging periods are both long, 23 and 33 days respectively. The female's visits to the chick are infrequent, brief, silent and inconspicuous. Many details of breeding behaviour indicate that the inconspicuousness of the nest is of paramount importance. The nestling is fed on fruit which the female regurgitates. The main breeding season is from April to July with a minor one in October and November. It takes two and a half years for the male to attain fully adult plumage, and at least two years to achieve a completely adult call. The relationship between type of nest, clutch-size, feeding habits and sexual bonds in tropical forest birds is discussed. The bellbird is an extreme example of a species in which the need for a very inconspicuous nest and a diet of fruit have combined to promote polygamy, with the emancipation of the male from the nest, and to reduce clutch-size to a minimum. The bellbird's structural adaptations to its method of feeding in flight are discussed and a comparison is made with the birds of paradise. The male's adaptations for its primary function of self-advertising are compared with the parallel adaptations evolved in the related Pipridae.     

Darwin's Finch Begging Intensity Does Not Honestly Signal Need in Parasitised Nests

Parental care should be selected to respond to honest cues that increase offspring survival. When offspring are parasitised, the parental food compensation hypothesis predicts that parents can provision extra food to compensate for energy loss due to parasitism. Chick begging behaviour is a possible mechanism to solicit increased feeding from attending parents. We experimentally manipulated parasite intensity from Philornis downsi in nests of Darwin's small ground finch (Geospiza fuliginosa) to test its effects on chick begging intensity and parental food provisioning. We used in‐nest video recordings of individually marked chicks to quantify nocturnal parasite feeding on chicks, subsequent diurnal chick begging intensity and parental feeding care. Our video analysis showed that one chick per brood had the highest parasite intensity during the night (supporting the tasty chick hypothesis) and weakest begging intensity during the day, which correlated with low parental care and rapid death. We observed sequential chick death on different days rather than total brood loss on a given day. Our within‐nest video images showed that (1) high nocturnal larval feeding correlated with low diurnal begging intensity and (2) parent birds ignored weakly begging chicks and provisioned strongly begging chicks. Excluding predation, all parasite‐free chicks survived (100% survival) and all parasitised chicks died in the nest (100% mortality). Weak begging intensity in parasitised chicks, which honestly signalled recent parasite attack, was not used as a cue for parental provisioning. Parents consistently responded to the strongest chick in both parasitised and parasite‐free nests.     

BREEDING NOTES ON THE BLACK-NECKED GREBE PODICEPS NIGRICOLLIS BREHM

Summary

Tarboton, W. R. &; Fry, C. H. 1986. Breeding and other behaviour of the Lesser Jacana. Ostrich 57: 233–243.

Breeding Lesser Jacanas were studied briefly at Lake St Lucia (Zululand), Hwange (Zimbabwe) and the Okavango Delta (Botswana). The species is monogamous and breeding birds are dispersed as territorial pairs. Male and female share incubation nearly equally, alternating at the nest in shifts averaging 39min; the eggs are attended (incubated or shaded), on average, for 82% of the daylight hours. Eggs are incubated by holding them against the breast with the underside of the wings; at least one chick was seen carried under a parent's wing. The pullus, foraging behaviour, courtship and vocalisations are described. It is suggested that the Lesser Jacana's small egg necessitates a high rate of nest attendance which could account for the sociosexual differences between this species and other jacanas.     

Sex-biased aggression and male-only care at sea in Brünnich's Guillemots Uria lomvia and Razorbills Alca torda

In several groups in the order Charadriformes, biparental care is followed by a period of male‐only care. Several hypotheses attempting to explain extended male parental care in shorebirds do not fit the Alcini. In a previous study of Brünnich’s Guillemots Uria lomvia and Razorbills Alca torda, we did not find support for female‐biased parental effort at the breeding site that would lead to males being in better condition to care for chicks at sea. However, in both species, males spent more off‐duty time at the breeding site than females, suggesting greater involvement in the defence of egg or chick, breeding site and mate. We predicted that there would be a male bias in size and aggressive behaviour associated with parental roles. To test this, body size and aggression of attending male and female Brünnich’s Guillemots and Razorbills were measured during incubation and brooding on the Gannet Islands, Labrador. Parental aggression was measured using natural observations of all agonistic interactions and, in Razorbills only, in situ responses to presentations of a predator model. In both species, males were significantly larger than females in culmen and gape length. Guillemot males initiated agonistic interactions more frequently than females during incubation. In contrast, female Guillemots were subjected to aggression more frequently than males and as a result were involved in more fights. In addition, the few chicks that were seen to die were being attended by single females. During the brooding period, Razorbill males responded aggressively to intruders more frequently than females, made more aggressive responses than females, and responded aggressively more frequently and more intensely than females to a predator model. In both species there was a similar male bias in morphology and behaviour that is consistent with male parents being more capable of protecting their chick, a probable advantage to chick survival during the uniparental care phase of some Charadriformes.     

An audio–visual nest monitoring system for the study and manipulation of siblicide in bearded vultures <Emphasis Type="Italic">Gypaetus barbatus</Emphasis> on the island of Crete (Greece)

We describe here an automated surveillance system that was installed in a bearded vulture (Gypaetus barbatus) nest in Crete during 2003–2006 with the aim of studying siblicide in this species. The system caused only minimal levels of disturbance to the birds and was capable of operating autonomously for more than 1 week. It comprised (1) a nest monitoring subsystem (camera, microphone, battery with a charge controller and a transmitter together with an antenna), which was supported by a solar panel, and (2) a recording subsystem (antenna receiver, video signal controller and a remote controlled PC through a GSM modem) that compressed the audio–video signal and provided real time monitoring. Two-egg clutches with a 7-day laying and hatching interval were recorded while hatching asynchrony was also determined through an analysis of the bioacoustic data. Food delivery rate and number of feeds to the first chick increased after the hatching of its sibling although not significantly so. Of the aggressive interactions recorded, 98% were initiated by the dominant chick and resulted in an average of 246 ± 157 peckings per day. Supplementary feeding did not produce any significant correlation between feeding rate and sibling aggression. The second chick survived 5 days and died as a result of starvation accelerated by sibling aggression. Intervention measures aimed at increasing the survival chance of the second chick should be undertaken when the latter is 1–2 days old.     

Revisiting the influence of aggressive interactions on the survival of the first‐laid egg in crested penguins (genus Eudyptes)

Crested penguins Eudyptes spp. have evolved a unique form of breeding in which the first of two eggs laid is much smaller than the second and has a higher likelihood of being lost during egg laying and incubation. In this study, we quantified aggressive behaviour in nesting Snares penguins and undertook an egg survival analysis to examine which factors influence egg loss. During 120 h of observation of 50 nests, we recorded a total of 300 aggressive events in which females were repeatedly pecked, bitten and beaten. Aggressive events lasted from less than a minute to up to 55 min (mean 4.6 ± 7.4 min). Single males were the aggressor in 75% of aggressive events and in 50.7% of aggressive events the aggressor was identified as a neighbouring, breeding male. A greater percentage of the small first eggs (34%) were lost than the large second eggs (4%). We found that egg mortality was influenced by 1) whether the other egg within a nest had hatched, 2) who was present at the nest (father, mother or both) and 3) the average duration of aggressive events on the nest. When one egg within a nest had hatched, the other egg had a vastly increased mortality risk irrespective of aggression. However, long, aggressive events directed towards females after their partners had gone foraging, also increased the probability of egg loss. We suggest that the prolonged nest attendance by breeding males well beyond egg laying is in response to the high frequency of aggressive behaviour during this time. Our data show that A‐egg losses occur due to intraspecific aggression in this species. Further research is needed to clarify whether aggressive behaviour in breeding crested penguins is modulated by elevated testosterone levels in the males and whether any reproductive benefits accrue to the aggressors.