Chicks In Broods Research Articles

Capelin (Mallotus villosus) as an important food source for northern fulmars (Fulmarus glacialis) breeding at Bjørnøya (Bear Island), Barents Sea

The food and feeding ecology of northern fulmars Fulmarus glacialis was investigated in July 1999 at Bjornoya (Bear Island). Fulmars relied almost exclusively on fish during the brooding period. The main fish prey was capelin Mallotus villosus (87.0% by reconstituted mass), Atlantic cod Gadus morhua accounting for most of the remainder (9.7% by reconstituted mass). The estimated total length of capelin and Atlantic cod eaten averaged 15 and 17 cm, respectively. Adult fulmars performed short foraging trips averaging 8 hours when brooding chicks, and they foraged at a mean maximum distance of about 60 km, the birds being concentrated on the shelf surrounding the island. The study emphasizes the importance of capelin as a key link between zooplankton and top predators, including seabirds, in the pelagic ecosystem of the Barents Sea.

Corticosterone facilitates begging and affects resource allocation in the black-legged kittiwake

Parent black-legged kittiwakes (Rissa tridactyla) and their dependent chicks respond to food shortages by increasing circulating levels of corticosterone. To examine the behavioral significance of corticosterone release, we experimentally increased levels of circulating corticosterone in parents and chicks up to the levels observed during food shortages. We found that corticosteroneimplanted chicks begged more frequently than sham-implanted controls. Corticosterone-implanted chicks in broods of two begged more frequently than singletons. Parent kittiwakes then responded to the increase in corticosterone levels in their chicks by increasing chick-feeding rates. However, feeding rates were not different among corticosterone-implanted chicks in broods of two and singletons. We also found that corticosterone-implanted parents spent more time away from the nest—perhaps foraging—and less time brooding/guarding chicks than sham-implanted controls. Untreated mates of the corticosterone-implanted bird did not compensate for the change in their partner’s behavior; consequently, chicks were left unattended about 20% of the time compared to 1% at the control nests. However, corticosterone-implanted parents did not decrease their chickfeeding rates. Our findings suggest two functional implications of the increased corticosterone secretion during food shortages in the black-legged kittiwake: it facilitates begging in chicks, and it affects time allocated by parents to guarding young at the nest. Thus, release of corticosterone might provide a mechanistic link between physiological condition and behavioral interactions among adults and their young. Key words: begging, corticosterone, food stress, kittiwakes, parent-offspring conflict, Rissa tridactyla, seabirds. [Behav Ecol 12:619–625 (2001)]

The effect of pup vocalisations on food allocation in a cooperative mammal, the meerkat ( Suricata suricatta )

In the meerkat (Suricata suricatta), a cooperative mongoose, pups follow potential feeders while the group is foraging and emit incessant calls when soliciting food from them. In contrast to a ’stationary’ brood of chicks, in which nestlings are fed at a fixed location, meerkat pups are ’mobile’ and become spread out. The question arises whether meerkat pups that experience different constraints to those facing chicks have evolved similar begging strategies. This paper describes the vocalisations that meerkat pups emit in the context of begging and investigates the influence of these calls on food allocation by older group members and on the behaviour of littermates. Meerkat pups use two types of calls when soliciting food from a potential feeder. The most common is a ’repeat’ call, which pups emit continuously when following an older forager over several hours a day. In addition, when a potential feeder finds a prey item, the pups next to it emit a bout of calls with increased calling rate, amplitude and fundamental frequency, termed ’high-pitched’ calls. Observations, together with playback experiments, showed that more prey was allocated to pups that called longer and more intensely. The pup closest to a feeder was almost always fed. The probability of emitting high-pitched calls did not depend on the time since a pup had received food, and the change from repeat to high-pitched calls occurred suddenly. The main function of the high-pitched call, therefore, does not appear to be to signal a pup’s hunger state. More likely, the two calls, in the context of begging, may be an adaptation to energetic constraints in a mobile feeding system. Pups, which are dispersed during foraging, may emit repeat calls over long periods to prevent potential feeders from eating all the prey themselves. At the moment a potential feeder finds prey, pups may give the more intense high-pitched calls to direct feeders to bring the food item to them and not to a littermate. Therefore, unlike the stationary feeding system where chicks emit one type of begging call when the feeder approaches the nest, meerkats, with a mobile feeding system, have evolved two discrete types of vocalisations in the context of begging.

Opposing selective pressures on hatching asynchrony: egg viability, brood reduction, and nestling growth

At least 19 hypotheses have been proposed to explain the evolutionary significance of avian hatching asynchrony, and hatching patterns have been suggested to be the result of several simultaneous selective pressures. Hatching asynchrony was experimentally modified in the black kite Milvus migrans by manipulating the onset of incubation during the laying period. Delayed onset of incubation reduced egg viability of first-laid eggs, especially when ambient temperature during the laying period was high. Brood reduction (nestling mortality by starvation or siblicide) was more commonly observed in asynchronous nests. The growth rate was slower in synchronous broods, probably due to stronger sibling rivalry in broods with high size symmetry. Last-hatched chicks in synchronous broods fledged at a small size/mass, while in control broods, hatching order affected growth rates, but not final size. Brood reduction, variable growth rates, and the ability to face long periods of food scarcity are probably mechanisms to adjust productivity to stochastic food availability in a highly opportunistic predator. The natural pattern of hatching asynchrony may be the consequence of opposing selective forces. Extreme hatching synchrony is associated with slow growth rates, small final size of last-hatched chicks, and low viability of first-laid eggs, while extreme hatching asynchrony is associated with high mortality rates. Females seem to facultatively manipulate the degree of hatching asynchrony according to those pressures, because hatching asynchrony of control clutches was positively correlated with temperature during laying, and negatively correlated with the rate of rabbit consumption.

Factors Affecting Nesting Success of Wood Thrushes in Great Smoky Mountains National Park

Recent evidence suggests that the nesting success of forest-interior Neotropical migrants is lower in fragmented habitat. We examined the nesting success of Wood Thrushes (Hylocichla mustelina) in a large contiguous forest from 1993 to 1997. From a sample of 416 nests we tested for predictors of daily nest survival rates, including activity at the nest and vegetation parameters at the nest site. We tested whether disturbance during nest checks (as measured by the behavior of the adults) was related to subsequent nest predation. Females were more likely to vocalize when brooding chicks than when incubating eggs. However, we found no evidence that observer disturbance or Wood Thrush activity influenced daily nest survival rates. Wood Thrushes nested predominately in small hemlocks, generally surrounded by many other small hemlocks. However, survival rates of nests in hemlocks were not significantly different from those in other substrates. Overall, neither activity at the nest nor habitat in the vicinity of the nest was a good predictor of nesting success, and only one vegetation characteristic, a measure of concealment, was significantly correlated with successful nesting. Brood parasitism by Brown-headed Cowbirds (Molothrus ater) was extremely low (<2% of nests parasitized). However, nesting success was moderate (daily survival rate = 0.958) when compared with other published studies from more-fragmented landscapes. Our results suggest that daily nest survival rates do not increase monotonically from small to very large forest patches.

Hatching asynchrony and food stress in Ring-billed Gulls: an experimental study

We examined predictions derived from three hypotheses (hurry-up, peak-load reduction, and brood reduction) regarding the adaptive significance of hatching asynchrony. The study was conducted, in 1991 and 1992, in a colony of Ring-billed Gulls (Larus delawarensis) on l'île de la Couvée, Montréal, Québec, Canada. The hypotheses were examined by comparing the mass and size of 18- to 20-day-old chicks from broods that hatched asynchronously (unmanipulated) and synchronously (manipulated). We also compared feeding rates and fledging success between asynchronous and synchronous broods. Also, in 1992, a sample of asynchronous and synchronous broods was experimentally food stressed by providing them with an additional chick when the oldest resident chick was 4 or 5 days old. Consistent with the hurry-up hypothesis, hatch spreads were significantly shorter in 1991 when the mean clutch initiation date was significantly earlier compared with 1992. Also consistent with the hypothesis, hatch spreads increased significantly through the breeding season. In agreement with the peak-load-reduction hypothesis, feeding rates were significantly lower in asynchronous broods compared with synchronous broods. Contrary to the hypothesis, however, the feeding rate was similar for food-stressed asynchronous and food-stressed synchronous broods. As predicted by the brood-reduction hypothesis, survivorship was higher for first-hatched chicks in asynchronous broods compared with chicks in synchronous broods. Total brood loss as a result of starvation tended to occur less often in asynchronous broods compared with synchronous broods. Likewise, fledging success was higher in asynchronous broods compared with synchronous broods. However, contrary to the brood-reduction hypothesis, survival rate of first-hatched chicks, total brood loss, and fledging success were similar in food-stressed asynchronous and synchronous broods. The above results indicate that several benefits accure to Ring-billed Gulls from hatching asynchrony.

Diet and survival of capercaillie Tetrao urogallus chicks in Scotland

The diet of young capercaillie Tetrao urogallus chicks in Scotland was assessed from analysis of their faeces, collected at the roost sites of broods with radio‐marked mothers. Lepidoptera larvae were their main invertebrate food and bilberry Vaccinium myrtillus their main plant food. The concentration of larval remains in the chicks' droppings was correlated with the abundance of larvae found by sweep netting in nearby vegetation. Broods of chicks with the greatest concentration of larval remains in their droppings survived best. Sweep netting for larvae in a semi‐natural pine forest in June 1991–1996 showed that larval size, abundance and timing differed among years, and that the sites with the most larvae also differed from year to year. In the same forest, we estimated capercaillie breeding success from hens and chicks found during dog counts. The average number of young per hen in July was correlated with the size, rather than the abundance, of larvae in mid June.

Hatching Asynchrony and Sibling Size Hierarchies in Gulls: Effects on Parental Investment Decisions, Brood Reduction and Reproductive Success

We manipulated the within-brood mass hierarchy of Lesser Black-backed Gulls Larus fuscus, controlling for chick quality (related to laying order) by swapping last hatched (c-) chicks in experimental broods with aor bchicks from residual broods to create either synchronous broods (all 3 chicks in the brood approximately the same mass) or asynchronous broods (same within-brood difference in mass between largest and smallest chicks as that of unmanipulated broods), whilst also controlling for variation in characteristics of parental quality (clutch size, egg size and timing of laying). Subsequent chick growth and survival for each brood were monitored in comparison with naturally asynchronous, unmanipulated broods in order to assess the effect of hatching asynchrony per se on chick growth and survival. There were no differences among treatments in fledging success or growth characteristics of surviving chicks. However, chick mortality occurred significantly later in synchronous broods and this was a consequence of the smaller within-brood hierarchical differences in size and body condition of these chicks. Apparently, parents could not regulate resource allocation in synchronous broods, and invested a greater amount of parental investment in chicks that later died. The results indicate that (1) the degree of hatching asynchrony may be optimized with respect to the prevailing food supply and/or female nutritional condition, and (2) the degree of hatching asynchrony is more important than initial within-clutch differences in egg or chick quality in determining the outcome of sibling rivalry over parental investment.

The Influence of Hatching Date on Different Life-History Stages of Great Skuas Catharacta skua

We investigated the effect of hatching date on chick body condition, chick survival, post-fledging survival and eventual breeding performance as an adult (laying date and clutch volume) of Great Skuas in Foula (Shetland). In 10 out of 16 years there was a seasonal decline in chick body condition. In the remaining years, there was no detectable effect of hatching date on chick condition. Differences among years were statistically significant. Chicks in early broods survived better than late-hatched chicks in four years, and no trend could be detected in one year. Annual variation in the seasonal pattern of chick growth and survival, and of adult territorial attendance, suggests that environmental conditions play a role in determining the seasonal decline in performance. Post-fledging survival in relation to hatching date was studied by analysis of ringing recoveries. Hatching date affected post-fledging survival, but only in the first year of life. Breeding parameters of birds of known hatching date were studied when they came back to breed in Foula. Hatching date of an individual did not affect its laying date or volume of the clutches laid later in life. This suggests that laying date has a low heritability, or none at all. Birds that laid early in the season produced more future recruits than later birds. After an early breeding attempt, skuas had a higher overwinter survival probability than after a late season. These results suggest that laying date is an indicator of individual quality in skuas, in the sense that early birds apparently are more competent at gathering resources for reproduction and survival.

The colonization of turkeys by thermophilic campylobacters.

The rate at which five broods of turkey chicks became colonized by thermophilic campylobacters was investigated. Day-old chicks were normally free of campylobacters on arrival on the farm with colonization beginning within 7 d. The carriage rate was 100% by day 14 in three of the broods and by day 21 in the other two. Higher carriage rates were obtained with enrichment procedures than with direct plating. Two broods were investigated over an extended interval for the number of campylobacters shed in their faeces. In brood A, Campylobacters increased from day l to day 14 concomitant with increase in the carriage rate and in the number of chicks with diarrhoea. By day 39, when the birds were sold to other farms, the excretion rate had reached 6 x 10(7) campylobacters g-1 fresh faeces. Brood B. was monitored over 91 d and showed peaks in Campylobacter numbers on days 19 and 75, corresponding to peaks in the number of diarrhoeic samples. The introduction of new birds into the brood resulted in an increase in the Campylobacter population and in the number of birds with diarrhoea. Campylobacter jejuni was the only species isolated but comprised several different biotypes. Analysis of the number of campylobacters at different sites along the gastrointestinal tract of mature turkeys at slaughter showed that numbers increased with distance from the beak and were highest in the caeca.

Quality vs. quantity: energetic and nutritional trade‐offs in parental provisioning strategies

1. When faced with increased brood demand, parent birds provisioning young in the nest can make a variety of adjustments to their foraging and food allocation strategies. Logical extensions of classic optimal foraging theory predict increased provisioning effort to larger broods to be accompanied by changes in load size, foraging distance from the nest, as well as possible changes in the type and size of prey delivered. 2. We assessed such behavioural adjustments and their consequences in pairs of European starlings (Sturnus vulgaris) responding to a range of experimental brood sizes. Parents feeding larger broods increased their visit rates by spending less time in the nestbox and less time around the nestbox colony. High visit rates to larger broods were also associated with larger loads per visit and changes in the type of prey delivered to the nest. As a consequence, chicks in large and small broods received similar rates of food intake, but experienced differences in the nutritional quality of their food. Parents feeding larger brood sizes were able to increase their provisioning effort despite feeding in the same foraging sites, travelling at comparable flight speeds and maintaining similar body masses to parents feeding smaller broods. 3. Parental energetic expenditure, measured through doubly labelled water analyses, showed no effect of the brood size treatment. The greater proportion of indigestible material per gram of food delivered to the larger experimental brood sizes (i.e. soil from the guts of earthworms) was probably responsible for the fact that these chicks grew at slower rates and fledged at lower body masses, although we cannot rule out the possibility of lower growth rates due to higher energetic costs of sibling competition within larger broods. Lighter fledglings from large broods disappeared from the local area earlier in the summer, probably as a result of differential mortality rather than premature natal dispersal. 4. We discuss the adaptive significance of the provisioning trade‐off between quantity and quality of food items delivered by parents to the nest, with reference to natural variation in foraging conditions and brood demand.

Release techniques and predation in the introduction of houbara bustards in Saudi Arabia

Experimental releases of captive-bred houbara Chlamydotis undulata macqueenii bustards were conducted at Mahazat as-Sayd Protected Area in western Saudi Arabia from 1992 to 1994. Three release techniques were tested: release of broods, release of feather-cut subadults and release of flying subadults. Releases were made in a 400 ha enclosure free of mammalian predators from where houbara were free to fly into the reserve. Approximately two-thirds of feather-cut subadults were killed by avian predators inside the enclosure, before they were able to fly. Chicks in broods also were susceptible to avian predation inside the release enclosure and mammalian carnivores outside the enclosure. However, 36% of chicks released were introduced successfully. Greatest success (48%) was achieved with flying subadult release. Experimental removal (translocation) of red foxes Vulpes vulpes and feral cats Felis domesticus from the vicinity of the release enclosure affected the temporal and spatial distribution of mammalian predation but not the overall rate. At the end of 1994, 35 introduced houbara were free-ranging in the reserve, some having been so for as long as 27 months, and they appeared to no longer be seriously threatened by predation.

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 chick9s 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.

Survival of Northern Bobwhite Chicks in Western Oklahoma

We estimated survival for chicks within 59 northern bobwhite (Colinus virginianus) broods using a modification of the Mayfield method that allows for brood mixing and intrabrood dependence. Broods were monitored during 1992-94 on the Packsaddle wildlife Management Area in western Oklahoma. Daily survival rates (DSR) were calculated for chicks reared by both female and male parents, chicks from hatching to 20 days old, chicks from 21 to 39 days old, chicks from hatching to 39 days old, by year, and pooled over years. Survival rates of brood mates were dependent on each other (P < 0.0001); therefore, the entire brood was the appropriate sampling unit for estimating variation associated with chick survival. Daily survival rate estimates for chicks in broods raised by females and males did not differ. Daily survival rates of chicks ≤20 days old were not significantly less than DSRs of chicks ≥21 days old. No differences were observed among years for DSR of chicks pooled over sexes ≤20 days old or chicks ≥21 days old (P = 0.9997). Chick DSR pooled over the entire brood-rearing period (x = 39 days, SE = 4.1 days) did not differ among years for either sex or pooled over sexes. Survival estimates pooled over sex and years for chicks from hatching to 20 days old and from 21 to 39 days old were 37.9 and 96.8%. The estimate of chick survival pooled over sex and years from hatching to 39 days was 36.7%.

Ground-roosting in domestic fowl ( Gallus gallus domesticus) in The Gambia: the anticipation of night

The ground-roosting behaviour of a semi-feral population of domestic hens with broods of chicks was measured in The Gambia, West Africa. Although neither day length nor time of sunset changed significantly over the duration of the study (January–March 1995), mean daily light intensity showed a significant increase. This resulted in an increasingly rapid decline in light intensity at dusk as the season progressed. Hens went to roost significantly later in the day, and at lower light levels, over the course of the season. The results support a model suggesting that the cue to start roosting is a certain light level, constant over the season, but the `settling period' required means that the hens finally roost at later times and at lower light levels as the season progresses.

Sex differences in the behaviour and measurements of CorncrakesCrex crexin Scotland

Radio‐tagged Corncrakes which incubated clutches and/or accompanied broods of chicks were not observed to sing. Birds which sang did not give parental care. Dissection of two birds which had been radio‐tracked indicated that the first group were females and the second group were males. This confirmed previous indications that, in the wild, only females care for the eggs and young and only males sing. The length of the head and bill and the maximum chord wing length were both greater in males than females. A linear discriminant function including these two measurements sexed 96% of birds correctly. Functions fitted separately to data from each of two study areas sexed 93% of birds correctly when applied to birds from the other area.

Mohua and stoats: A population viability analysis

Abstract Population viability analysis was used to assess the survival prospects of mohua (Mohoua ochrocephala) populations of varying sizes, with different breeding strategies and suffering predation episodes at varying frequencies, from the South Island of New Zealand. Mohua populations in which most pairs attempted to raise two broods of chicks each year were more vulnerable to episodic stoat (Mustela erminea) predation than were populations in which pairs attempted to raise only one brood. However, those populations in which most pairs raised two broods had a much better ability to recover following predation. High stoat numbers every year would lead to the extinction of mohua populations regardless of their size and breeding strategy, but one‐brood populations would decline more slowly. If stoat populations were high only once every 5 years (the likely natural rate in South Island beech forests), small populations, and populations in which most pairs raised only one brood a year, would have very low survival prospects, but two‐brood populations of more than about 40 pairs would have good survival prospects. Reduction in stoat densities, particularly in years when their numbers are high, is likely to have a substantial positive effect on mohua populations.

The function of hatching asynchrony in the blue-footed booby

The blue-footed booby (Sula nebouxii) commonly hatches two eggs 4 days apart; then the senior (first-hatched) chick aggressively dominates the other and sometimes kills it. Two hypotheses explaining the function of the hatching interval were tested by creating broods with synchronous hatching: the facultative brood reduction hypothesis of Lack (1954) and the sibling rivalry reduction hypothesis of Hahn (1981). The results contradicted most predictions of both hypotheses: synchronous broods formed an aggressive hierarchy similarly to asynchronous broods (controls), and subordinate chicks grew poorly (Fig. 1) and died frequently, similarly to junior chicks in control broods. However, compared with synchronous broods, asynchronous broods showed less aggression (Fig. 2), diminished food allocation to subordinate chicks (Fig. 3) and less total food consumption (30% fewer feeds at age 0–10 days). These behavioral comparisons took into account the different ages of chicks in different treatments. The results suggest that natural asynchrony makes brood reduction more efficient and decreases the costs of sibling aggression to parents, in terms of their future survival or fecundity, as proposed by Mock and Ploger (1987). Further, in exaggeratedly asynchronous broods (8-day hatch interval) junior chicks suffered more aggression (Fig. 4) and grew more slowly than junior chicks in control broods. This result supports the hypothesis of optimal hatch asynchrony of Mock and Ploger (1987).

Costs and benefits of brood desertion in female kentish plovers, Charadrius alexandrinus

Female kentish plovers Charadrius alexandrinus typically desert their broods after the chicks hatch, i.e. 1–4 weeks before the chicks fledge or become independent. In this paper we investigate the costs and benefits of desertion for females. Desertion incurs a cost for females: following desertion chick survival in broods is lower (0.95 +- 0.02 day−1) than before the female deserts (0.98 +- 0.01 day−1). We investigated several possible causes for reduced brood survival by comparing characteristics of broods before and after desertion (controlling for differences in brood age). After desertion males increased the time they spent foraging and they tended to reduce time spent brooding chicks. Increased mortality of chicks may occur in deserted broods because following desertion (1) males spend less time alert in vigilance behaviour than before desertion, (2) they attend the chicks from greater distances, and (3) they show greater distraction display distances (in response to human intruders). Growth or development of chicks, measured by weight gain and tarsus length, was not different before and after desertion. Females gain two potential benefits from desertion: (1) they may remate and produce a second brood within the same breeding season or (2) they may enhance their probability of surviving to breed in a subsequent season. At least 27% of female kentish plovers that deserted remated and renested in the same season in this study. In contrast, we found no evidence that brood desertion increased the survival of females: there was no difference in local survival rate (return rate) for females deserting before or after 6 days brood age. These results clearly demonstrate that female kentish plovers that desert their offspring prior to fledging incur costs, but we suggest that there is a trade-off with the potential benefits gained by remating and making a second breeding attempt in the same season.

Differences in reproductive success and parental qualities between habitats in the Great Tit Parus major

Reproductive success and parental attributes of Great Tits Parus major nesting in good and poor habitats were compared to investigate whether they differed and, if so, whether parental or environmental variation contributed most to the differences.Monitored over 3 years, clutches in mature woodland were started earlier, were larger and produced larger broods of heavier chicks than those in marginal habitats such as gardens and hedgerows. Fledging success was significantly higher in woodland in 2 of the 3 years although egg weights were lower. Parents nesting in different habitats were very similar in body‐size although those in woodland were in better condition. The prey delivered to nestlings in woodland was of significantly higher quality than that delivered in marginal habitats. Furthermore, the heritability of body‐size (tarsus‐length) was higher in woodland, suggesting that the environment limits nestling growth in poorer habitats. Reproductive success was considerably lower in poor habitats and appears to be constrained primarily by environmental quality, although this may operate partly through its affect on parental body condition.