The breeding biology and causes of nest failure of Scottish Black-throated Divers Gavia arctica

The breeding biology and causes of nest failure were examined for Black-throated Divers Gavia arctica in core areas of their Scottish breeding range in 1983–1987. Breeding was confirmed for up to 88% of territorial pairs each year ( n = 28–62), and 76% of nests were on islands. Hatching success was consistently low with, on average, only 43% of territorial pairs managing to hatch a clutch each year; 64% of recorded nest failures occurred during the first week of the 4-week incubation period.
Overall breeding success in West Sutherland in 1984–1987 averaged 0.23 chicks per territorial pair per year, while in Ross-shire for 1986–1987 it was 0.29. Forty percent of hatched chicks survived to fledge, and 92% of recorded deaths occurred in the first fortnight after hatching; 4.8% of fledged broods held two chicks.
Causes of nest failure were assessed with the aid of surveillance cameras. Approximately 30% of losses were due to water level changes (mostly floods), 48% to predators (primarily nocturnal mammals, but also Hooded Crows Corvus corone ), 13% to human egg collectors and 5% to desertion following human disturbance.
Scottish Black-throated Divers produce only half the number of chicks tentatively estimated to be required to maintain a stable population. The main difference between the Scottish and more successful Swedish populations is in the degree of chick mortality.     

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.     

Development of chicks and predispersal behaviour of young in the Eagle Owl Bubo bubo

Little quantitative information on the development and behaviour of chicks and young is available for many species, despite the crucial importance of such data and the sensitivity of this stage in a bird's life. For Eagle Owls Bubo bubo , despite the large amount of scientific literature on this species, much basic information is lacking. This study provides a photographic and morphometric guide for age estimation of nestlings and fledglings, as well as data on the call behaviour of young, and patterns of movements during the post-fledging dependence period. The most remarkable event in chick development is the rapid increase in mass, and size gain, during the first 30 and 40–45 days, respectively. Because after this time morphometric differences become less evident, young-feather development is more useful for ageing. Patterns of chick call behaviour showed that the time spent calling increased with age and, from 110 days of age, chick vocalizations were usually uniformly distributed through the whole night and most synchronized at sunset and sunrise (the maximum recorded number of vocalizations per chick and per night was 1106 calls). During the post-fledging dependence period, radiotagged Owls moved widely, up to 1500 m from the nest after the age of 80–90 days. During such movements, the mean distance among siblings increased with age, from 168 m on average for juveniles less than 100 days old, to 489 m for those older than 100 days. Definitive dispersal started when young were about 150–160 days old. Information on chick call behaviour and movements is crucial for unbiased census and nest checking, as well as for the definition of young post-fledging areas. Knowledge of the latter is very important in terms of conservation and management (especially for those species that move largely around their nest before dispersal) owing to the high mortality that can occur during this period.     

Behaviour of the yellow-eyed penguin chick

The ontogeny of yellow-eyed penguin ( Megadyptes antipodes ) chick behaviour follows the order of development determined by Nice (1962) for several species of birds, and by Spurr (1975) for the Adélie penguin ( Pygoscelis adeliae ). Feeding and comfort behaviours are the first to develop, followed by locomotion and aggressive behaviour.
Active solicitation of food may occur at one day of age. Chicks initially use non-visual cues to mediate begging. After their eyes open on the third or fourth day there is an increase in the use of visual stimuli, and begging occurs most often following adult nest relief. Sibling rivalry is not intense, occurring least during feeding, and in general both chicks are fed at each session.
The chicks are brooded for the first 21–25 days. At sparsely vegetated nest sites overheating may occur after 21 days and down-covered chicks will seek shade and pant in hot weather.
Throughout the 6–7 weeks of the guard phase there is a decrease in the amount of time spent resting in a prone posture, and an increase in exploratory, locomotory behaviour. During the post-guard phase, and until fledging and independence at 15 weeks after hatching, chicks may wander up to 20 m from the nest bowl during exploration, shade-seeking and feeding.
Adults feed only their own chicks, and chicks appear to beg only from their parents. Dense vegetation and long distances between nests tend to restrict contact between adults and chicks from neighbouring nests, and prevent the formation of large chick crèches.     

Feeding frequency influences crèching age in the Dalmatian pelican, Pelecanus crispus

Crèching behaviour is common in colonial seabirds; nevertheless, the factors inducing chicks to aggregate remain relatively poorly understood. It has been proposed that brood size, laying date and nest attendance are important factors in the formation of a crèche. Moreover, in most species of pelicans, chicks join crèches following the development of homoeothermy and coincident with the end of the brooding behaviour. We studied effects of feeding rate, nest attendance, brood size, laying date and homoeothermy on the age at which chicks entered the crèche at a colony of Dalmatian pelicans (Pelecanus crispus), in Srebarna, Bulgaria. Single chicks were fed more frequently than chicks from two-chick broods. Unlike American white pelicans (Pelecanus erythrorhynchos), Dalmatian pelicans maintained brooding behaviour a further 9 days after chicks had developed thermoregulation abilities. In contrast to nests with two chicks, nests with only one chick were never left unattended by the parents before the chick reached the crèching stage. Laying date, nest attendance and brood size did not affect the age that the chick entered the crèche. The age the chick entered the crèche was not correlated with the age of homoeothermy acquisition, but chicks significantly joined the crèche at younger ages when the mean number of feeds per chick per day during the rearing period in the nest was higher. This result suggests an implication of growth rate in the crèching age. Joining the crèche earlier can provide benefits that could have strong implications for the chicks’ future reproductive lives.     

Golden Plover Pluvialis apricaria breeding success on a moor managed for shooting Red Grouse Lagopus lagopus

Capsule The best estimate of breeding success was a mean of 0.57 fledglings per pair, which when combined with adult survival rates, successfully explained the observed population trend.

Aims To quantify Golden Plover breeding success on a moor managed for shooting Red Grouse Lagopus lagopus.

Methods An intensive study recorded the fate of individual Golden Plover nests and, using radiotelemetry, chicks. The factors associated with mortality were examined, allowing the construction of a model of breeding success. Adult survival was estimated from return rates of colour-ringed birds.

Results Estimated rates of daily nest survival during laying (0.8636) were significantly lower than during incubation (0.9913). The daily survival rate of chicks less than nine days (0.8868) was significantly lower than for older chicks (0.9792). A population model based on these parameters overestimated the rate of nest losses, but accurately described brood survival and fledging success. Although predation rates were low, poor survival of young chicks through starvation or exposure suggest other factors were limiting breeding success at the study site.

Conclusions Predation rates of Golden Plover nests and chicks can be low on moorlands managed for shooting Red Grouse. However, in the absence of predation, other factors may still reduce chick survival and limit breeding success.     

Breeding biology of the thin-billed prion<Emphasis Type="Italic"> Pachyptila belcheri</Emphasis> at New Island,Falkland Islands: egg desertion,breeding success and chick provisioning in the poor season 2002/2003

We present data on breeding success, chick growth and chick feeding in thin-billed prions, Pachyptila belcheri, at New Island, Falkland Islands, in the breeding season 2002/2003. As in many populations of seabirds in the region, the overall breeding success was very low. This was mainly caused by low rate of observed burrow occupancy (60%) and hatching (57%) of thin-billed prions, while chick survival was closer to normal. Sixty-eight percent of the chicks survived to fledging. In total, a chick was successfully reared in 23% of the nests or from 38% of recorded eggs. The failed eggs were found to be incubated for 30 days, on average. The time of egg desertion coincided with the time of desertion of other seabirds at New Island, with a period of high sea-surface temperatures and low catch rates by the commercial fisheries. We describe chick growth and use repeated weighings, corrected for metabolic loss, to estimate meal sizes. Chicks were fed a mean 39.2 g in 77% of the nights. We discuss possible reasons for the observed extremely low hatching success, and compare with the breeding success of other seabirds at the Falkland Islands.     

Survival analysis of Little Penguin Eudyptula minor chicks on Motuara Island, New Zealand

Chick survival of Little Penguins Eudyptula minor was studied on predator-free Motuara Island, Cook Strait, New Zealand (41̀05'S, 174̀15'E), in 1995 and 1996. We used the Kaplan-Meier estimator and robust Cox regression to estimate chick survival rate (pL se) at 0.325 pL 0.044, leading to an estimated survival from laying to fledging of 0.13 or a reproductive output of 0.26 chicks per pair and breeding attempt. Starvation posed the greatest mortality risk, followed by unknown factors and rain. Risk of death due to rain was restricted to the guard stage, whereas starvation occurred throughout the nesting period, though with a peak in the early guard stage. Significant seasonal differences in survival rate were detected in both years, but with reversed trends, survival decreasing with the season in 1995 and increasing in 1996. Failure of adults to relieve their partner on the nest after chicks hatched accounted for 16% mortality or 34% of all chick deaths. Differences in chick survival rate between nest types were significant in 1995, a year with high rainfall, but not in 1996. Nests in the base of hollow trees had the highest chick survival rate. Of chicks in open nests - a nest type that is unusual for this species - 5.4% fledged. Our results suggest that on Motuara Island good breeding sites are scarce and that the food supply has been poor during the years of this study.     

Effects of color banding, radio tagging, and repeated handling on the condition and survival of Lapwing chicks and consequences for estimates of breeding productivity

ABSTRACT.   Color bands and radio tags are widely used to facilitate individual recognition and relocation of precocial chicks in studies of prefledging survival. However, the accuracy of data collected and subsequent estimates of survival rates rely on the assumption that such techniques do not affect the parameters under study. We compared the body condition and survival of color-banded and radio-tagged Lapwing ( Vanellus vanellus ) chicks with noncolor-banded and nonradio-tagged individuals using a 10-year dataset ( N = 3174 chicks, with 205 color banded and 700 radio tagged). Color bands did not adversely affect chicks. However, radio-tagged chicks and their untagged broodmates were handled more frequently because these broods were more readily encountered than those without a tagged member. Chicks disturbed and handled more frequently had lower body condition indices and higher mortality rates. Simulations of the impact of tagging and handling on breeding productivity under two scenarios indicated a 26% reduction in productivity in situations where nest and chick survival rates were low (as in our study), but only a 7% reduction in productivity for a simulated population with the higher levels of nest and chick survival associated with a stable population. The frequent disturbance associated with radio-tracking and recapturing chicks, rather than the attachment of a tag or physical handling of chicks, may affect body condition. Frequent handling and disturbance may affect body condition by reducing foraging time, increasing stress levels, or increasing predation risk. Because our results suggested that the negative impact of handling could last up to a week, we recommend that investigators avoid disturbance of shorebird chicks more frequently than every 8 d.     

Reproductive biology of the endangered Ouvea Parakeet Eunymphicus cornutus uvaeensis

The reproductive biology of the endangered Ouvea Parakeet Eunymphicus cornutus uvaeensis , an endemic subspecies of Ouvea island (Territory of New Caledonia, Southwest Pacific) was studied from June 1994 to February 1996. Breeding was recorded from early August until late January. All nests were sited in cavities of native forest trees, 90% of them in Syzygium sp. and Mimusops sp. Mean clutch size was 2.9 eggs (range 2–3), and double clutches were recorded. Incubation lasted 21 days and the nestling period averaging 43 days. An average of 1.65 chicks fledged per nest but only 0.75 per breeding pair were still alive 30 days after fledging. The main causes of chick loss were starvation of the third sibling during the first week due to hatching asynchrony, raptor (presumably Brown Goshawk) predation of fledglings and human harvest for the pet trade. Growth curves and multiple regressions of weight, culmen-width and -length, tarsus- and wing-length, showed that wing-length was a good predictor of age, and that there were significant differences between the sexes for weight and culmen-width. The pattern of the breeding season, brood reduction, nest-site characteristics and presumed size of breeding territories suggest that both food and availability of suitable nest-sites may be factors limiting breeding productivity. Proposals for conservation of this endangered bird are presented.     

Hatching asynchrony,sibling hierarchies and brood reduction in the Chinstrap penguin Pygoscelis antarctica

We studied patterns of chick growth and mortality in relation to egg size and hatching asynchrony during two breeding seasons (1991 and 1992) in a colony of chinstrap penguins sited in the Vapour Col rookery, Deception Island, South Shetlands. Intraclutch variability in egg size was slight and not related to chick asymmetry at hatching. Hatching was asynchronous in 78% (1991) and 69% (1992) of the clutches, asynchrony ranging from 1 to 4 days (on average 0.9 in 1991 and 1.0 days in 1992). Chicks resulting from oneegg clutches grew better than chicks in families of two in 1991. In 1992, single chicks grew to the same size and mass at 46 days of age as chicks of broods of two, suggesting food limitation in 1991 but not in 1992. In 1991, asymmetry between siblings in mass and flipper length was significantly greater in asynchronous than in synchronous families during the initial guard stage, but these differences disappeared during the later créche phase. In 1992, asymmetry in body mass increased with hatching asynchrony and decreased with age. Only the effect of age was significant for flipper length and culmen. Asymmetries at 15 days were similar in both years, but significantly lower in 1992 than in 1991 at 46 days of age. There were relatively frequent reversals of size hierarchies during both phases of chick growth in the two years, reversals being more common in 1991 than in 1992 for small chicks. In 1991, survivors of brood reduction grew significantly worse than chicks in nonreduced broods. In both years, chicks of synchronous broods attained similarly large sizes before fledging as both A and B chicks of asynchronous broods. In 1991, chick mortality rate increased during the guard stage due to parental desertions, decreased during the transition to crèches (occurs at a mean age of 29 days) and returned to high constant levels during the crèche stage, when it is mostly due to starvation (in total 66% of hatched chicks survived to fledging). In contrast, in 1992, mortality was relatively high immediately after hatching and almost absent for chicks older than 3 weeks (87% of chicks survived to fledging). Mortality affected similarly one- and two-chick families. In 1991, asynchronous families suffered a significantly greater probability of brood reduction than synchronous families, but this probability was not significantly related to degree of asymmetry between siblings. No association between asynchrony and mortality was found in 1992. These results show that there is food limitation in this population during the crèche phase in some years, that asynchronous hatching does not facilitate early brood reduction and that it does not ensure stable size hierarchies between siblings. Brood reduction due to starvation is not associated to prior asymmetry and does not facilitate the survival or improve the growth of the surviving chick. Asynchronous hatching may be a consequence of thermal constraints on embryo development inducing incubation of eggs as soon as they are laid.     

Field Studies Using European Starlings to Establish Causality between PCB Exposure and Reproductive Effects

Accumulation and effects of polychlorinated biphenyls (PCBs) in avian species were evaluated at a Superfund site located at Crab Orchard National Wildlife Refuge, Illinois, and seven criteria were used to assess whether there was a causal relationship between PCB exposure and observed reproductive effects. European starlings (Sturnus vulgaris) were monitored at nest boxes constructed at each of two exposed and two reference sites. During the breeding season, starling productivity (number of chicks produced per nest) and adult nest attentiveness behavior (provisioning behavior) were monitored. At 15 days post-hatch, chicks were collected for contaminant and biomarker analyses. Chicks were necropsied, ethoxyresorufin-O-deethylase (EROD) activity measured in liver tissue, and PCB (Aroclor 1254) and 34 chlorinated biphenyl (CB) congener concentrations measured in carcasses using gas chromatography. PCB and CB concentrations also were measured in eggs that failed to hatch. Mean Aroclor 1254 and quantified CB concentrations were greater (P<0.001) in eggs that failed to hatch and 15-day-old chicks collected from PCB sites compared to those collected from reference sites. EROD activity was greater (P=0.005) in 15-day-old chicks collected from PCB sites and was correlated with carcass PCB concentrations. Reduced adult nest attentiveness behavior and decreased chick survival were observed at PCB sites. Six of the seven causal criteria evaluated provided evidence that observed reproductive effects resulted from exposure to PCBs. Using this weight-of-evidence approach provided a means for establishing the likely cause of effects and thus provided managers with information needed in decision-making processes.     

Reproductive success of wild Lesser Rheas (Pterocnemia -Rhea- pennata pennata) in north-western Patagonia, Argentina

We studied the reproductive success of a wild Lesser Rhea population (Pterocnemia -Rhea- pennata pennata) during two reproductive seasons (2004/2005 and 2005/2006) in north-western Patagonia, Argentina. The parameters recorded included population and nest density, clutch size, hatching success, chick survival (up to 3 months of age) and percentage of chicks that reached the juvenile stage after the winter. We also estimated the percentage of males that attempted to nest and of those that were successful (those producing at least one chick), daily nest mortality rates (DNMR) at different stages of the nesting cycle and the probability that an egg that has been recently laid will produce a chick. On average, both years pooled, the density of this population of Lesser Rheas was 1.55 ± 0.2 individuals/km² (SE), nest density was 0.17 ± 0.04 per km ² , clutch size was 20.8 ± 6.4 eggs, hatching success was 74.4% ± 11.3, Mayfield’s probability of an egg that will produce a chick was 0.64, chick survival was 65.4% ± 14.5 and percentage of chicks that reached the juvenile stage was 26.3%. Nearly a quarter of Lesser Rhea males in the population attempted to nest during a breeding season, and the DNMR was significantly higher during the laying stage (most nest failures were due to anthropogenic disturbances related to livestock raising activities). Nesting success, hatching success, and chick survival of Lesser Rheas were higher than those of their most closely related species, the Greater Rhea (Rhea americana), whereas the percentage of chicks that reached the juvenile stage was similar due to high winter mortalities of chicks. We suggest that the increase in reproductive effort is a strategy of this species to overcome environmental constraints.     

Regulation of parental investment in the Antarctic petrel Thalassoica antarctica: an exchange experiment

An experiment was conducted on the Antarctic petrel to test whether the parents were able to respond to changes in food demand of their offspring. Two experimental groups were formed by replacing eight 20-day-old chicks with 10-day-old chicks, and vice versa. The growth rate of chicks in the experimental groups was compared with that in two control groups with chicks of known age. The growth rate of 10-day-old chicks in the nests of parents which initially had 20-day-old chicks did not differ significantly from that in their respective control groups. This indicates that those parents were able to raise a new young nestling, despite having already raised another chick from hatching to 20 days. However, the 20-day-old chicks placed in nests with 10-day-old chicks had a significantly lower growth rate than their control group. Feeding rate per day and nest did not differ significantly among any of the groups. This suggests that the observed difference in growth rate between 20-day-old chicks is related to a lower amount of food delivered per visit to experimental chicks. Thus, in the Antarctic petrel, the feeding rate apparently is not regulated by the status of the chick, but by the parents' ability to gather food or willingness to provide food for the chicks.Publication no. 137 from the Norwegian Antarctic Research Expedition (NARE) 1989/90     

Exclusion of ground predators improves Northern Lapwing Vanellus vanellus chick survival

Many farmland‐breeding wader species have declined across Europe, probably due to reductions in reproductive output caused by high nest losses as a result of agriculture or predation, or low chick survival between hatching and fledging. Most studies have focused on nest failures, and the factors affecting post‐hatching survival of chicks are poorly known. In an experimental approach, we fenced parts of the arable foraging areas of Northern Lapwing Vanellus vanellus families to quantify chick survival simultaneously in the presence and absence of ground predators. Lapwing chicks were radiotagged to estimate survival probabilities by daily locations, applying multistate capture–recapture models. During the night, chick survival was considerably lower outside fenced plots than within. During the day, chick survival was higher than at night and did not differ between protected and unprotected plots. This suggests that nocturnal ground predators such as Red Foxes Vulpes vulpes were responsible for a significant proportion of chick mortality. Cumulative survival probability from hatching to fledging was 0.24 in chicks within fenced plots, but virtually zero in chicks outside fenced plots. In farmland, temporary electric fences can be effective in minimizing the impact of ground predators and offer a promising short‐term method to increase fledging success of precocial birds.     

Chick survival in relation to nest site: is the Antarctic petrel hiding from its predator?

In birds, the characteristics of the nest site may affect reproductive success. We found that shelter is an important characteristic of the Antarctic petrel (Thalassoica antarctica) nests because shelter prevents chick predation. However, the benefit of shelter was countervailed by melt water which mainly entered well-sheltered nests. Chick survival was monitored until the chick was left unattended for the first time. Late-hatched chicks had a higher survival probability than early-hatched chicks, possibly because late hatchers swamp the predator, the south polar skua (Catharacta maccormicki). Poorly sheltered nests tended to be occupied by parents with low body mass and late-hatched eggs. The results suggest that both shelter per se and parental characteristics may explain the relationship between predation risk and shelter. We need experiments to study the influence of nest site on reproductive success, and we need to map the frequency of melt water as a cause of reproductive failure.     

Influence of Climate Change on Productivity of American White Pelicans,Pelecanus erythrorhynchos

In the past decade, severe weather and West Nile virus were major causes of chick mortality at American white pelican (Pelecanus erythrorhynchos) colonies in the northern plains of North America. At one of these colonies, Chase Lake National Wildlife Refuge in North Dakota, spring arrival by pelicans has advanced approximately 16 days over a period of 44 years (1965–2008). We examined phenology patterns of pelicans and timing of inclement weather through the 44-year period, and evaluated the consequence of earlier breeding relative to weather-related chick mortality. We found severe weather patterns to be random through time, rather than concurrently shifting with the advanced arrival of pelicans. In recent years, if nest initiations had followed the phenology patterns of 1965 (i.e., nesting initiated 16 days later), fewer chicks likely would have died from weather-related causes. That is, there would be fewer chicks exposed to severe weather during a vulnerable transition period that occurs between the stage when chicks are being brooded by adults and the stage when chicks from multiple nests become part of a thermally protective crèche.     

Effect of the blood-sucking mite

Pathological consequences of the blood-sucking mite Ornithonyssus bursa vary between species, with its impact ranging from no measurable effect, to significant blood loss and chick mortality. In New Zealand, where several bird species are known to be parasitised by O.bursa, the effect of this mite on host fitness is unclear, as few studies have been carried out. During a three-year study of the North Island robin Petroica longipes on Tiritiri Matangi Island, the prevalence of O. bursa in robin nests and on chicks and its impact on robin chick growth and survival was measured. The presence of mites was correlated with both time of the season and humidity of the habitat, with infestation being positively correlated with later nesting attempts and more humid microclimates. Robin chicks in infested nests were significantly smaller and fledged at an earlier age than chicks in nests where no mites were detected. Despite this effect, no significant difference in body size or survival was detected between the two groups at one month post-fledging. This was most likely because chicks from mite- infested nests compensated for their retarded growth once they left the nest environment. On mainland New Zealand, where ground-dwelling mammalian predators are present, chicks forced to leave the nest at an earlier age with less developed flying skills may be at an increased risk of predation.     

Brood reduction in the Blue-eyed Shag Phalacrocorax atriceps

Brood reduction is common in a population of Blue-eyed Shags on Signy Island, South Orkney Islands. This paper describes possible adaptations which may reduce the brood. In clutches of three, the last egg was smaller, and hatched 2.4 days later than its siblings. Whilst 78–84% of first and second ('A' & 'B') chicks fledged, only 11 % of 'C' chicks did. In a sample of artificially synchronized broods chick survival was as high as in normal asynchronously hatching broods, but there were more cases of total brood loss. The age at which the C chick died was related inversely to the length of the A-C hatching interval. Relative differences in sibling weights were highest during the first 12 days, when most of the C chick deaths occurred. At this age the daily food requirements of each brood of three was one-tenth that of each brood of two just prior to fledging. It is suggested that C chicks were unable to compete effectively for a food supply which was limited by the parents, rather than by the environment. The asymptotic weight attained by A chicks was inversely related to brood size, and was greater than that of B or C chicks. Normal asynchronous broods produced at least one heavy (A) chick and one medium weight (B) chick, whilst in synchronized broods the asymptotic weight attained was similar to that of B chicks in normal broods.     

Behavioural ecology of the North Sulawesi Tarictic Hornbill Penelopides exarhatus exarhatus during the breeding season

Two nests of the North Sulawesi Tarictic Hornbill Penelopides exarhatus exarhatus were monitored for one breeding season (April-July). The females sealed themselves into the nest cavities and remained there for 70–90 days. Incubation was estimated at 16–19 days, and at both nests two offspring fledged. Tarictic Hornbills are cooperative breeders with up to three helpers at the nest and defend foraging territories of 72–139 ha. Food items delivered to the nest included fruits of 34 species (85% of diet items) and invertebrates. Provisioning by helpers allowed breeding males to reduce investment in parental care and may accelerate the development rates in chicks. Constraints on dispersal probably result from habitat saturation rather than living in an unpredictable environment.