Synchronous Broods Research Articles

Functional explanation of extreme hatching asynchrony: Male Manipulation Hypothesis.

Hatching asynchrony in birds is considered an adaptation to facilitate brood reduction because under conditions of food scarcity, the smallest nestling usually dies soon after hatching, thereby minimizing parental effort. However, in species with extreme hatching asynchrony, the last hatchlings paradoxically experience a very low probability of survival and death can take so long that it can hardly be considered an adaptation. Here, we propose and experimentally tested a new adaptive hypothesis explaining the brood reduction paradox, namely the “Male Manipulation Hypothesis”. Our hypothesis suggests that by inducing asynchronous hatching, females increase the feeding requirements of the brood, which will induce males to increase provisioning effort. In addition, females may extend the period of male manipulation by feeding the smallest nestling just enough to sustain life. Our study showed that male common blackbirds (Turdus merula) increased their effort (i.e., number of food items per hour) in experimental asynchronous broods compared to synchronous broods, while females reduced their contribution, as predicted by the hypothesis.

Azure‐winged Magpies Cyanopica cyanus trade off reproductive success and parental care by establishing a size hierarchy among nestlings

It is common in birds that the sizes of nestlings vary greatly when multiple young are produced in one nest. However, the methods used by parents to establish size hierarchy among nestlings and their effect on parental provisioning pattern may differ between species. In the Azure‐winged Magpie Cyanopica cyanus, we explored how and why parents controlled the sizes of nestlings. Asynchronous hatching was the main cause of size hierarchy within the brood, although the laying of larger eggs later in the laying sequence reduced this effect. Parents with asynchronous broods produced more eggs and fledged more nestlings than those with synchronous broods but their brood provisioning rates, food delivery per feeding bout and feeding efficiency did not differ. We performed a cross‐fostering experiment to synchronize some asynchronous broods. Provisioning rates of asynchronous broods were lower than those of synchronized broods, but the daily growth rates and fledging body mass of their nestlings were not different. Our findings indicate that parents of asynchronous broods can achieve higher reproductive success than those of synchronous broods based on the same parental care, and the same reproductive success as those of synchronized broods based on less parental care. It appears that parent birds can better trade off reproductive success and parental care by establishing a size hierarchy among nestlings.

An experimental approach to the brood reduction hypothesis in Magellanic penguins

In many bird species, eggs in a brood hatch within days of each other, leading to a size asymmetry detrimental to younger siblings. Hatching asynchrony is often thought of as an adaptive strategy, and the most widely studied hypothesis in relation to this is the ‘brood reduction hypothesis’. This hypothesis states that when food resources are unpredictable, hatching asynchrony will allow the adjustment of the brood size maximizing fledging success and benefitting parents. The Magellanic penguin Spheniscus magellanicus is an appropriate species to test this hypothesis because it has a 2‐egg clutch that hatches over a 2‐d interval with a broad range of variation (–1 to 4 d), it shows facultative brood reduction, and food abundance between breeding seasons is variable. We performed a manipulative study at Isla Quiroga, Argentina, during three breeding seasons (2010–2012) by forcing broods to hatch synchronously (0 d) or asynchronously (2 or 4 d). Years were categorized based on estimated food abundance. Our study provided mixed results because in the low estimated food abundance year asynchronous broods did not have higher nestling survival than synchronous broods, and the second‐hatchling in asynchronous broods did not die more often than those in synchronous broods. On the other hand, younger siblings of 4‐d asynchronous broods starved earlier than those of synchronous broods, and 2‐d asynchronous broods fledged heavier young than synchronous broods. Asynchronous hatching would seem to benefit reproduction in this species, not with respect to survival, but in terms of the advantages it can accord to nestlings and, in terms of lower costs, for parents raising nestlings.

Within-female plasticity in sex allocation is associated with a behavioural polyphenism in house wrens.

Sex allocation theory assumes individual plasticity in maternal strategies, but few studies have investigated within-individual changes across environments. In house wrens, differences between nests in the degree of hatching synchrony of eggs represent a behavioural polyphenism in females, and its expression varies with seasonal changes in the environment. Between-nest differences in hatching asynchrony also create different environments for offspring, and sons are more strongly affected than daughters by sibling competition when hatching occurs asynchronously over several days. Here, we examined variation in hatching asynchrony and sex allocation, and its consequences for offspring fitness. The number and condition of fledglings declined seasonally, and the frequency of asynchronous hatching increased. In broods hatched asynchronously, sons, which are over-represented in the earlier-laid eggs, were in better condition than daughters, which are over-represented in the later-laid eggs. Nonetheless, asynchronous broods were more productive later within seasons. The proportion of sons in asynchronous broods increased seasonally, whereas there was a seasonal increase in the production of daughters by mothers hatching their eggs synchronously, which was characterized by within-female changes in offspring sex and not by sex-biased mortality. As adults, sons from asynchronous broods were in better condition and produced more broods of their own than males from synchronous broods, and both males and females from asynchronous broods had higher lifetime reproductive success than those from synchronous broods. In conclusion, hatching patterns are under maternal control, representing distinct strategies for allocating offspring within broods, and are associated with offspring sex ratios and differences in offspring reproductive success.

Hatching Asynchrony and Spring Climatic Conditions in the European Roller

Hatching asynchrony (HA hereafter) leads to patent age and size hierarchies within broods of altricial birds, disadvantaging runts through a reduced condition/survival. The function of HA is controversial, although a general hypothesis states that HA would be an adaptive maternal mechanism for maximizing reproductive output under particular ecological conditions. Accordingly, when ecological conditions are not favourable, asynchronous broods would outperform synchronous broods because the formers would allow for an adaptive adjustment of brood size. A poorly untested prediction emerging from this hypothesis is that the adaptive value of HA should change with environmental conditions in relatively long time windows within a population. Using data from 8 years of a population of the asynchronous European roller Coracias garrulus, we studied variation in HA and fecundity selection on HA. Hatching span (ranging from 1 to 8 days) was longer in larger broods and later in the breeding season. Interestingly, we found that asynchronous broods were more fecund than synchronous ones in colder and drier years in April, which is the previous month to reproduction, and the opposite was true in years with warmer but rainier Aprils. Given that warmer and rainier Aprils relate to advanced and increased arthropod availability in the Mediterranean region, these results would suggest that HA in rollers might function as an adaptive trait that provides parents of asynchronous broods with some benefits in years with low productivity, in agreement with the Lack’s brood reduction hypothesis, and illustrate the relevance of studying the adaptive value of HA over gradients of environmental conditions.

Hatching Asynchrony Decreases the Magnitude of Parental Care in Domesticated Zebra Finches: Empirical Support for the Peak Load Reduction Hypothesis

AbstractParent–offspring conflict over the supply of parental care results in offspring attempting to exert control using begging behaviours and parents attempting to exert control by manipulating brood sizes and hatching patterns. The peak load reduction hypothesis proposes that parents can exert control via hatching asynchrony, as the level of competition amongst siblings is determined by their age differences and not by their growth rates. Theoretically, this benefits the parents by reducing both the peak load of the offspring's demand and their overall demand for food and benefits the offspring by reducing the amplification of their competition. However, the peak load reduction hypothesis has only received mixed support. Here, we describe an experiment where we manipulated the hatching patterns of domesticated zebra finch Taeniopygia guttata broods and quantified patterns of nestling begging and parental feeding effort. There was no difference in the begging intensity of nestlings raised in asynchronous or experimentally synchronous broods, yet parental feeding effort was lower when provisioning asynchronous broods and particularly so when levels of nestling begging were low. Further, both parents acted in unison, as there was no evidence of parentally biased favouritism in relation to hatching pattern. Therefore, our study provided empirical support for the prediction that hatching asynchrony reduces the feeding effort of parents, thereby providing empirical support for the peak load reduction hypothesis.

Breeding synchronization facilitates extrapair mating for inbreeding avoidance

Extrapair (EP) mating can enable females to reduce the negative effects of inbreeding. However, opportunities for EP mating are often ecologically or demographically constrained, and it is unclear whether and how females can overcome these constraints. Here, we show that fitness costs from inbreeding in purple-crowned fairy-wrens (Malurus coronatus) are severe (≥30% reduction in hatchability of eggs in incestuous pairs). Although EP paternity was low for unrelated pairs (3% of broods), and negatively affected by low breeding density, 46% of broods produced by incestuously paired females contained EP young that were almost always sired by a direct neighbor. Moreover, females in incestuous pairs initiated egg laying more synchronously with direct neighbors than females in an unrelated pair, and more synchronous broods were more likely to contain EP young. Because male sperm stores are highest around their own partner’s fertile period, our results imply that incestuously paired females achieve high levels of EP paternity by adjusting the timing of egg laying to match peak fertility of neighboring males. This example of a dramatic increase in EP paternity due to subtle behavioral adjustments illustrates that negative effects of inbreeding exert strong selection for female strategies to facilitate EP mating, and this may contribute to unexplained variation in EP paternity.

The adaptive function of hatching asynchrony: an experimental study in great tits

In many bird species offspring hatch over hours or days, which leads to an age and size hierarchy within broods. The function of hatching asynchrony is much debated, and it has been suggested that the induced size hierarchy among offspring may be an adaptive maternal mechanism for maximizing reproductive output under variable environmental conditions. The best known hypothesis to explain the adaptive value of hatching asynchrony, the ‘brood reduction’ hypothesis, holds that a size hierarchy among offspring allows for a quick adaptive adjustment of brood size to unpredictable feeding conditions and thus benefits parents. To test the consequences of hatching asynchrony on offspring growth and food provisioning we experimentally manipulated the onset of incubation of eggs within broods of great tits, Parus major , to induce either synchronous or asynchronous hatching, and then manipulated brood size after hatching to simulate favourable, control or harsh conditions. We did not find a difference in offspring mortality between asynchronous and synchronous broods under any of these conditions. In harsh conditions, nestling mass and size were reduced in asynchronous broods compared to synchronous ones. The opposite pattern occurred under control conditions. Although our results showed that induced hatching asynchrony alters offspring phenotype, they do not provide strong support for the brood reduction hypothesis as a mechanism to explain hatching asynchrony. • We tested the adaptive value of hatching asynchrony in great tits. • We induced either synchronous or asynchronous hatching. • We simultaneously manipulated the rearing conditions by changing brood size. • Nestling mortality did not differ between asynchronous and synchronous broods. • In enlarged broods, nestlings in asynchronous broods were lighter and smaller. • Our results do not support the brood reduction hypothesis.

Hatching asynchrony and offspring sex influence the subsequent exploratory behaviour of zebra finches

The ecological and evolutionary consequences of variation in behaviour between individuals are well studied, yet the causes of such variation remain poorly understood. Parents can generally exert a great deal of influence on the early life of their offspring, so one possibility is that the mode of parental investment determines subsequent offspring behaviours. In birds, hatching asynchrony occurs when females begin incubation prior to clutch completion, and the subsequent hatching regime creates phenotypic disparities between early and late-hatched offspring. By experimentally manipulating hatching patterns in zebra finches, Taeniopygia guttata, we examined the influence of hatching asynchrony on subsequent exploratory behaviour during adulthood. Late-hatched birds from asynchronous broods explored the novel environment more than their siblings which hatched earlier or came from synchronous broods, although there were no differences in exploratory behaviour towards a novel object. Additionally, females were bolder towards a novel object than were males, independently of hatching regime, but there were no sex differences in exploration of the novel environment. Our results support the idea that both hatching asynchrony and sex have previously underappreciated influences on offspring behaviours, and highlight the importance of variation in parental investment in generating and maintaining behavioural variation.

Asymmetric contests at the nest

Hatching asynchrony of nestling birds leads to weight asymmetries, which in turn affect the nestlings’ relative success when competing for feedings brought to the nest. We present a game theoretic model that predicts how weight asymmetry influences the nestlings’ energy on securing feedings, thus determining the caloric value remaining for weight gain as well as the distribution of feedings obtained. The model has a unique Evolutionary Stable Strategy (ESS) profile, in which nestlings in more asymmetric nests exhibit less aggression and hence achieve larger weight gain per feeding. The impetus for this model was data from a long-term study of Arabian babblers (Turdoides squamiceps) that showed a surprising negative correlation between the number of feedings that a nest received and the overall weight gain in the nest. This finding is, however, entirely consistent with our model—in more symmetric nests, the individuals fight more and are consequently hungrier and beg for additional food, are fed more, but still gain less weight due to the higher energetic costs of fighting. The model provides a fundamental explanation also for related findings in other species, in which chicks in asynchronous broods were found to be heavier than those from synchronous broods. In addition, it supports the sibling rivalry hypothesis by which brood asynchrony may diminish aggressive interactions among nestlings, leading to more efficient use of resources.

Hatching asynchrony can have long-term consequences for offspring fitness in zebra finches under captive conditions

Hatching asynchrony can have profound short-term consequences for offspring, although the long-term consequences are less well understood. The purpose of this study was to examine the long-term consequences of hatching asynchrony for offspring fitness in birds. Specifically, we aimed to test the hypothesis that hatching asynchrony increases the sexual attractiveness and fecundity, respectively, of early-hatched male and female zebra finch, Taeniopygia guttata (Vieillot, 1817) offspring. Mate-choice trials comparing male nestlings with the same parents, but that were reared in asynchronous or experimentally synchronous broods, revealed no female preference in relation to hatching regime. We did however find strong evidence that, as adults, late-hatched males were more attractive to females than siblings that had hatched earlier. Meanwhile, we found a weak trend towards early-hatched females depositing more carotenoids and retinol in the egg yolk than late-hatched or synchronously hatched females, although there were no differences in terms of clutch characteristics or the deposition of α-tocopherol or γ-tocopherol in the egg yolk. Therefore, we found that the beneficial long-term consequences of hatching asynchrony were sex specific, being accrued by late-hatched male nestlings and by early-hatched female nestlings. Consequently, we conclude that the long-term consequences of hatching asynchrony are more complex than previously realised.

An experimental study of fledging success in American Coots (Fulica americana): Effects of brood size, food availability, and hatching asynchrony

ABSTRACT. Brood size and hatching patterns in birds are widely believed to represent adaptations to food availability during the brood-rearing period. Experimental manipulations of brood size and hatching patterns have been widely employed to determine whether parents can raise larger or more synchronous broods, but concurrent manipulations of food abundance to test the supposed causal mechanism have been rare. I studied survival to fledging of 1,060 American Coot (Fulica americana) chicks from 99 broods for which brood size, hatching asynchrony, and food availability had been experimentally manipulated via inter-nest transfers of newly hatched young and provisioning of supplemental food. Survival of color-marked young was measured until 45 days posthatch using Cormack-Jolly-Seber mark—resighting models. Survival of offspring from unsupplemented broods declined linearly with experimental increases in brood size, and this decline was large enough to ameliorate any benefits to parents from larger broods. Ho...

The adaptive benefit of hatching asynchrony in wild zebra finches

The evolutionary consequences of parent–offspring conflict have received considerable attention, yet the extent to which parent–offspring conflict influences life history traits remains uncertain. In particular, it is unclear whether hatching patterns are parental strategies to manipulate competitive dynamics among offspring, or whether they are instead consequences of physiological or ecological variables affecting the payoffs of adjusting the onset of incubation. Here we describe an experiment in which we manipulated the hatching pattern of wild free-living zebra finches. We examined the consequences of hatching pattern on parental feeding behaviour and sibling competition, with the aim of identifying selective pressures that underlie differing hatching patterns. Increasing hatching asynchrony reduced the overall quantity of food that parents delivered and the equitability of its distribution among nestlings compared with synchronous broods. However, for each unit of food received, the begging intensity of nestlings from asynchronous broods was lower. As a consequence, the growth rate of first-hatched nestlings in asynchronous broods was significantly greater than those in synchronous broods, and there was no significant difference in growth rate between last-hatched nestlings in asynchronous broods and nestlings from synchronous broods, even though they received less food overall. The reduced scramble competition and energy wasted on begging behaviour in asynchronous broods supports the sibling rivalry hypothesis, suggesting an adaptive function for hatching asynchrony in wild zebra finches.

Adaptive Sex Allocation in Relation to Hatching Synchrony and Offspring Quality in House Wrens

Increased variance in the reproductive success of males relative to females favors mothers that optimally allocate sons and daughters to maximize their fitness return. In altricial songbirds, one influence on the fitness prospects of offspring arises through the order in which nestlings hatch from their eggs, which affects individual mass and size before nest leaving. In house wrens (Troglodytes aedon), the influence of hatching order depends on the degree of hatching synchrony, with greater variation in nestling mass and size within broods hatching asynchronously than in those hatching synchronously. Early-hatching nestlings in asynchronous broods were heavier and larger than their later-hatching siblings and nestlings in synchronous broods. The effect of hatching order was also sex specific, as the mass of males in asynchronous broods was more strongly influenced by hatching order than the mass of females, with increased variation in the mass of males relative to that of females. As predicted, mothers hatching their eggs asynchronously biased first-laid, first-hatching eggs toward sons and late-laid, late-hatching eggs toward daughters, whereas females hatching their eggs synchronously distributed the sexes randomly among the eggs of their clutch. We conclude that females allocate the sex of their offspring among the eggs of their clutch in a manner that maximizes their own fitness.

Features of begging calls reveal general condition and need of food of barn swallow (Hirundo rustica) nestlings

Altricial offspring of birds solicit food provisioning by complex begging displays, implying acoustic and visual signals. Different components of begging behavior may function as reliable signals of offspring state and thus reproductive value, on which parents base optimal parental decisions about allocation of critical resources (e.g., food). We experimentally manipulated components of general condition of nestling barn swallows (Hirundo rustica) by (1) altering brood size by cross-fostering an unbalanced number of nestlings between pairs of synchronous broods and thus manipulating the level of within-brood competition for food, (2) injecting some nestlings with a harmless immunogen, simulating an infection, and (3) preventing part of the nestlings from receiving food for a short period while establishing control groups. We recorded rate of begging response by individual nestlings as parents visited the nest and recorded begging calls using a DAT recorder to analyze six sonagraphic features of vocalizations. Our factorial experiment revealed that nestlings deprived of food begged more frequently when parents visited the nest compared to their non--food-deprived nest mates. Food deprivation increased duration of syllables forming begging calls, whereas brood size enlargement resulted in increased latency of response to parental calls. Heavy nestlings in good body condition vocalized at a relatively low peak frequency. To our knowledge, this is the first study in which begging rate and sonagraphic structure of begging calls are shown to reliably reveal a diverse set of components of offspring general state, on which parental decisions may be based. Copyright 2002.

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.

Effects of short-term hunger and competitive asymmetry on facultative aggression in nestling black guillemots Cepphus grylle

Siblings in a diversity of species are facultatively aggressive, yet the proximate control of the aggressive response and the ecological conditions selecting for such systems are poorly understood. In this study, we investigated the effects of food amount (food amount hypothesis) and competitive asymmetry on sibling aggression in black guillemot broods. Parental provisioning rates were experimentally manipulated in broods comprising a range of hatching intervals over a 12-h period. Aggression became evident only after parental provisioning rates were experimentally reduced. When parental provisioning resumed, adults did not increase their feeding rate to compensate for the induced food deficit, and the result of sibling rivalry was a change in the allocation of parental deliveries from one of equality to one in favor of the dominant chick. Food-deprived chicks from synchronous broods were more aggressive than those from asynchronous broods, suggesting that one benefit of hatching asynchrony in the black guillemot is to establish an efficient competitive hierarchy among siblings which minimizes the need for costly aggressive interactions. On the following day, sibling aggression ceased, and chicks regained an equal share of parental feeds. Our results provide the first evidence that short-term food shortage per se acts as an initial trigger for aggression and also show that the aggressive response is complicated by factors associated with hatching and laying order. Key words: black guillemot, Cepphus grylle, competitive asymmetry, facultative aggression, hatching asynchrony, provisioning, sibling rivalry. [Behav Ecol 11: 282–287 (2000)]

Hatching asynchrony in the Eurasian kestrel Falco tinnunculus: an experimental test of the brood reduction hypothesis

Summary 1. We tested the brood reduction hypothesis by manipulating hatching spans of Eurasian kestrel Falco tinnunculus (Linnaeus) broods during two low vole years (1996–97) in western Finland. In addition, half the broods in 1997 were food supplemented during the entire nestling period. 2. Nestling mortality was high, occurring in 55% of nests, and the effect of manipulated hatching span on fledging success was more pronounced than either the effects of year or supplementary food. In contrast to the predictions tested, fledging success was higher in synchronous than asynchronous nests, both when food was limiting and when food conditions were substantially improved by food supplements. 3. We found no evidence that brood reduction resulted in higher quality (body mass) of surviving young in low vole years. On average, fledglings were heavier at synchronous than asynchronous nests. This was only the case, however, when food was limiting. 4. Most nestling mortality occurred when the chicks were 2 weeks old, and age of death did not differ between the brood types. Parents at synchronous nests fed their broods at a higher rate than at asynchronous broods, this divergence arising only in the latter part of nestling period. 5. This is the first hatching span experiment where synchronous hatching seemed more profitable than asynchronous during conditions of both food scarcity and food abundance. The higher parental workload at synchronous nests could, however, counterbalance the benefits of synchronous hatching. 6. Hatching in natural broods of Eurasian kestrel is more synchronous in low vole years compared to high vole years. The fact that synchronous broods out‐performed asynchronous broods in both ‘low’ years of the study is consistent with the facultative manipulations. The benefit of asynchrony in high vole years is still unclear.

Some Aspects of the Common Tern (Sterna Hirundo) Breeding Biology on the Kretuonas Lake Island

The research was carried out on the Didžioji Island, Lake Kretuonas, Aukstaitija National Park. The results obtained showed no remarkable differences between the centre and the periphery of the colony concerning predation on Common Terns (Sterna hirundo). Just embryo mortality (number of not hatched out eggs) was reliably higher in the periphery than in the centre. The most successful hatching of chicks and their survival within the first days after hatching were recorded for the tern nests with the eggs laid during the mass egg-laying season. In synchronous and asynchronous three-chick broods, survival of nestlings varied. In asynchronous broods, the last chicks grew slower due to sibling competition, percentage of their mortality being highest of all. In two- and three-chick broods, feeding intensity of each chick was, in general, similar and depended just on individual features of a certain pair and the abundance of food resources. It was due to a louder vocal stimulation that adults brought up food to...

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.