Last-hatched Nestlings Research Articles

Effects of brood and group size on nestling provisioning and resource allocation in a communal bird

Abstract Resource limitations, either due to environmental conditions or constraints on parental provisioning effort, can drive intense competition among offspring. In communal groups, resource availability may increase if parents receive assistance from other group members; however, if those caregivers also produce young, offspring demand may increase at the same time. It is possible, therefore, that the costs of intrabrood competition in large broods may outweigh the benefits of provisioning from additional caregivers. We tested the relationships between group size, brood size, and provisioning rates in the greater ani (Crotophaga major), a communally nesting cuckoo in which multiple breeding pairs and nonreproductive helpers cooperatively raise a shared brood. Crucially, brood and group size can vary independently in this species, allowing us to test changes in each variable separately. Using video footage of 2255 prey deliveries across 10 nests, we found that an increase in the number of adult caregivers within a group did not sufficiently offset a corresponding increase in the number of dependent young within a brood: prey availability per average nestling decreased with brood size, regardless of group size. In larger broods, last-hatched nestlings received significantly less prey than their broodmates, in part due to greater hatching asynchrony that exacerbated competitive asymmetries and facilitated inequality in food allocation. Our results indicate that last-hatched ani nestlings suffer a “double cost” in large broods: they must compete with more nestmates, and suffer disproportionately from asynchronous hatching. These costs may contribute to increased parent–offspring conflict and may constrain group size in communal breeders.

Hungry or angry? Experimental evidence for the effects of food availability on two measures of stress in developing wild raptor nestlings.

Food shortage challenges the development of nestlings; yet, to cope with this stressor, nestlings can induce stress responses to adjust metabolism or behaviour. Food shortage also enhances the antagonism between siblings, but it remains unclear whether the stress response induced by food shortage operates via the individual nutritional state or via the social environment experienced. In addition, the understanding of these processes is hindered by the fact that effects of food availability often co-vary with other environmental factors. We used a food supplementation experiment to test the effect of food availability on two complementary stress measures, feather corticosterone (CORTf) and heterophil/lymphocyte ratio (H/L) in developing red kite (Milvus milvus) nestlings, a species with competitive brood hierarchy. By statistically controlling for the effect of food supplementation on the nestlings' body condition, we disentangled the effects of food and ambient temperature on nestlings during development. Experimental food supplementation increased body condition, and both CORTf and H/L were reduced in nestlings of high body condition. Additionally, CORTf decreased with age in non-supplemented nestlings. H/L decreased with age in all nestlings and was lower in supplemented last-hatched nestlings compared with non-supplemented ones. Ambient temperature showed a negative effect on H/L. Our results indicate that food shortage increases the nestlings' stress levels through a reduced food intake affecting both their nutritional state and their social environment. Thus, food availability in conjunction with ambient temperature shapes between- and within-nest differences in stress load, which may have carry-over effects on behaviour and performance in further life-history stages.

Sex-specific effects of hatching order on nestling baseline corticosterone in a wild songbird

Variation in nestling growth and survival is often influenced by hatching order, with first-hatched offspring having an advantage over later-hatched younger siblings. In house wrens (Troglodytes aedon), this effect of hatching order is especially evident in asynchronously hatched broods and can lead to sex-specific differences in the size and condition of nestlings. Females appear to allocate the sex of their offspring across the laying order to capitalize on these differences. We hypothesized that levels of circulating corticosterone, the primary metabolic hormone in birds, mediates these sex-specific effects in nestlings. We predicted that: i) baseline levels of corticosterone in nestlings should vary along the hatching order, ii) effects of hatching order on baseline corticosterone should be sex specific, and iii) any sex-specificity of hatching order on baseline corticosterone could be contingent on the degree of hatching synchrony. We tested these predictions in a study in which we measured baseline corticosterone in first- and last-hatched nestlings in synchronously and asynchronously hatching broods. To assess whether any differences in nestling baseline corticosterone levels could be attributed to pre-natal maternal effects, the post-natal environment, or both, we conducted two additional studies in which we measured i) yolk corticosterone in first- and last-laid eggs and ii) baseline corticosterone in nestlings that were cross-fostered to create simulated ‘asynchronously’ hatched broods. There was a significant interaction between sex and relative hatching order in their effects on nestling baseline corticosterone, but no effect of hatching synchrony. Corticosterone levels remained relatively constant across the hatching order in males but decreased in females. There was a significant effect of laying order on yolk corticosterone, with first-laid eggs containing significantly higher levels of yolk corticosterone than last-laid eggs. Cross-fostering of nestlings at different points of development had no significant effect on nestling corticosterone levels. These results indicate that sex-dependent differences in corticosterone levels across the hatching order may arise, at least in part, from embryonic exposure to maternally derived corticosterone, whereas the post-natal rearing environment plays, at best, a minimal role in determining nestling baseline corticosterone levels.

Weather and food availability additively affect reproductive output in an expanding raptor population

The joint effects of interacting environmental factors on key demographic parameters can exacerbate or mitigate the separate factors’ effects on population dynamics. Given ongoing changes in climate and land use, assessing interactions between weather and food availability on reproductive performance is crucial to understand and forecast population dynamics. By conducting a feeding experiment in 4 years with different weather conditions, we were able to disentangle the effects of weather, food availability and their interactions on reproductive parameters in an expanding population of the red kite (Milvus milvus), a conservation-relevant raptor known to be supported by anthropogenic feeding. Brood loss occurred mainly during the incubation phase, and was associated with rainfall and low food availability. In contrast, brood loss during the nestling phase occurred mostly due to low temperatures. Survival of last-hatched nestlings and nestling development was enhanced by food supplementation and reduced by adverse weather conditions. However, we found no support for interactive effects of weather and food availability, suggesting that these factors affect reproduction of red kites additively. The results not only suggest that food-weather interactions are prevented by parental life-history trade-offs, but that food availability and weather conditions are crucial separate determinants of reproductive output, and thus population productivity. Overall, our results suggest that the observed increase in spring temperatures and enhanced anthropogenic food resources have contributed to the elevational expansion and the growth of the study population during the last decades.

The Influence of Biological Factors on Haematological Values in Wild Marsh Harrier (Circus aeruginosus) Nestlings.

Simple SummaryHaematological examination can be used to address the health state of birds. The present study aimed to investigate how hatching order, brood size, and nest initiation date influence the haemoglobin level, red blood cell count, white blood cell count, and glucose level in the blood of raptor nestlings in which brood reduction occurs during nestling rearing. Blood samples were collected to assess the health status of wild marsh harrier nestlings in the agricultural landscape of eastern Poland. Statistical analyses revealed that hatching order, but not brood size or nest initiation date, had an impact on the haematological data of nestlings. Hatching order affected these data in that haemoglobin levels and red blood cell counts gradually decreased, whereas glucose levels and white blood cell counts increased, from the first- to the last-hatched nestlings. The poor condition of the youngest nestlings reflected in these indices may increase the likelihood of their perishing, and consequently, of brood reduction.Marsh harrier (Circus aeruginosus) is a species with obligatory cainism, in which hatching asynchrony creates a pronounced size hierarchy in nestlings. The size-related competitive advantage of older nestlings means that they tend to dominate the younger ones, and brood reduction occurs in most nests. The aim of the study was to reference values and carry out a haematological examination in order to evaluate the physiological status and health of nestlings with respect to hatching order, brood size, and nest initiation date. To do so, we examined 19 nests with a total of 58 nestlings from a free-living population of this species located in fishpond complexes in the agricultural landscape of eastern Poland. Repeated blood samples (118 in all) were collected from nestlings. The following parameters were measured using fresh full blood: red blood cell count (RBC), haemoglobin level (Hb), white blood cell count (WBC), and plasma glucose level (Glu). The data were analysed using generalized linear mixed models and linear mixed models ((G)LMM). The study revealed that hatching order, but not brood size or nest initiation date, affected the physical condition of marsh harrier nestlings. Hb levels and RBC counts gradually decreased, whereas Glu levels and WBC counts increased from the first- to the last-hatched nestlings. This result points to the generally poorer condition of the youngest nestlings compared with their older siblings. The poor physiological condition of the youngest nestlings may consequently increase the likelihood of their perishing, and hence, of brood reduction.

Minutes matter: brief hatching asynchrony adversely affects late-hatched hihi nestlings, but not life beyond the nest

Size hierarchies are often seen when nestlings hatch asynchronously over a period of days. Shorter hatch periods are common across passerines, however, and while these may also give rise to asymmetries, their effects are rarely considered. Regardless of hatch period, the long-term consequences for later hatched nestlings that survive to fledge is unknown for wild birds. Here we explored the timing of hatch order in a free-living population of hihi nestlings, Notiomystis cincta, and followed any effects in and out of the nest. We found that while hatching time from first- to last-hatched nestlings was often less than 24 h, last-hatched individuals grew more slowly and were lighter and smaller at fledging than older siblings. Last-hatched nestlings were also less likely to fledge. These effects were greater in larger broods. Adult body size is correlated with fledging size in hihi; however, we found no evidence that hatch order affected longevity postfledging, or lifetime reproductive success. We then explored whether carotenoid availability might buffer these stressful rearing conditions (through food supplementation of parents) but found no evidence that increased access to carotenoids for mothers and/or growing nestlings influenced incubation schedules, or the effects of hatching late. Together these results suggest that while even a very short hatch period can influence adult phenotype, hatching asynchrony is not maladaptive for hihi: when last-hatched nestlings survive to fledge they can contribute as much to their mothers' fitness as first-hatched siblings.

Starting with a handicap: effects of asynchronous hatching on growth rate, oxidative stress and telomere dynamics in free-living great tits.

A trade-off between resource investment into growth rate and body self-maintenance is likely to occur, but the underlying molecular mediators of such a trade-off remain to be determined. In many altricial birds, hatching asynchrony creates a sibling competitive hierarchy within the brood, with first-hatched nestlings enjoying substantial advantages compared to last-hatched nestlings. We used this opportunity to test for a trade-off between growth and self-maintenance processes (oxidative stress, telomere erosion) in great tit nestlings, since resource availability and allocation are likely to differ between first-hatched and last-hatched nestlings. We found that despite their starting competitive handicap (i.e. being smaller/lighter before day 16), last-hatched nestlings exhibited growth rate and mass/size at fledging similar to first-hatched ones. However, last-hatched nestlings suffered more in terms of oxidative stress, and ended growth with shorter telomeres than first-hatched ones. Interestingly, growth rate was positively related to plasma antioxidant capacity and early life telomere length (i.e. at 7 days old), but among last-hatched nestlings, those exhibiting the faster body size growth were also those exhibiting the greatest telomere erosion. Last-hatched nestlings exhibited elevated levels of plasma testosterone (T), but only at day 7. T levels were positively associated with oxidative damage levels and plasma antioxidant capacity, the latter being only significant for first-hatched nestlings. Our results suggest that last-hatched nestlings present a specific trade-off between growth rate and self-maintenance processes, which is possibly driven by their need to compete with their older siblings and potentially mediated by elevated levels of T.

Impacts of parasites in early life: contrasting effects on juvenile growth for different family members.

Parasitism experienced early in ontogeny can have a major impact on host growth, development and future fitness, but whether siblings are affected equally by parasitism is poorly understood. In birds, hatching asynchrony induced by hormonal or behavioural mechanisms largely under parental control might predispose young to respond to infection in different ways. Here we show that parasites can have different consequences for offspring depending on their position in the family hierarchy. We experimentally treated European Shag (Phalacrocorax aristoteli) nestlings with the broad-spectrum anti-parasite drug ivermectin and compared their growth rates with nestlings from control broods. Average growth rates measured over the period of linear growth (10 days to 30 days of age) and survival did not differ for nestlings from treated and control broods. However, when considering individuals within broods, parasite treatment reversed the patterns of growth for individual family members: last-hatched nestlings grew significantly slower than their siblings in control nests but grew faster in treated nests. This was at the expense of their earlier-hatched brood-mates, who showed an overall growth rate reduction relative to last-hatched nestlings in treated nests. These results highlight the importance of exploring individual variation in the costs of infection and suggest that parasites could be a key factor modulating within-family dynamics, sibling competition and developmental trajectories from an early age.

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.

Yolk testosterone and estradiol variation relative to clutch size, laying order and hatching asynchrony in Common Grackles

Maternal effects are typically thought to enhance rather than reduce offspring performance, but asynchronous hatching (ASH) in birds typically produces a size hierarchy within a clutch that frequently reduces the growth and survival of nestlings from eggs that hatch later. Given that yolk steroids can significantly affect offspring phenotype and that in many species the levels of yolk steroids have been found to increase with laying order, the maternal transfer of steroids to egg yolk has been proposed as a mechanism for females to offset the deleterious effects of ASH. To test this hypothesis, we determined whether yolk steroids varied with laying order or clutch size in Common Grackles (Quiscalus quiscula). Because ASH varies with clutch size (hatching span averages 48 h in five-egg clutches, 24 h in four-egg clutches) and regularly results in the starvation of later hatched nestlings, we predicted: (1) testosterone and 17s-estradiol levels should increase with laying order in both clutch sizes to mitigate the negative effects of ASH on last-hatched nestlings, and (2) the increase should be greater in five-egg clutches due to more pronounced hatching asynchrony. Using a competitive-binding steroid radioimmunoassay, we found no systematic variation in either testosterone or estradiol levels relative to laying order or clutch size. In the absence of evidence that yolk steroids interact adaptively with ASH, research must look elsewhere for potential benefits that might compensate for the costs these steroids impose on nestlings.

LAYING-SEQUENCE VARIATION IN YOLK CAROTENOID CONCENTRATIONS IN EGGS OF YELLOW-HEADED BLACKBIRDS (XANTHOCEPHALUS XANTHOCEPHALUS)

Abstract Asynchronous hatching creates a size hierarchy among siblings and a survival disadvantage for last-hatched nestlings. Female birds can influence this disadvantage by differentially investing maternal resources, such as carotenoids, across the laying sequence. We studied intraclutch variation in carotenoid concentrations in Yellow-headed Blackbirds (Xanthocephalus xanthocephalus) and predicted that yolk concentrations would decrease across the laying sequence, because nestling mortality is inversely related to hatching order in this species. We quantified intraclutch variation in the concentrations of total and individual identifiable carotenoids (β-carotene, β-cryptoxanthin, lutein, and zeaxanthin) in Yellow-headed Blackbird eggs collected from five breeding colonies, and correlated these concentrations with egg mass, yolk mass, and yolk water content. Carotenoid concentrations were not related significantly to any of the egg metrics measured. The concentration of total identifiable carotenoids i...

Sex allocation and nestling survival in a dimorphic raptor: does size matter?

Fisher’s theory predicts equal sex ratios at the end of parental care if the costs and benefits associated with raising each sex of offspring are equal. In raptors, which display various degrees of reversed sexual size dimorphism (RSD; females the larger sex), sex ratios biased in favor of smaller males are only infrequently reported. This suggests that offspring of each sex may confer different fitness advantages to parents. We examined the relative returns associated with raising each sex of offspring of the brown falcon Falco berigora, a medium-sized falcon exhibiting RSD (males approximately 75% of female body mass) and subsequent sex ratios. Female nestlings hatched either first or second did not receive more food nor did they hatch from larger eggs or remain dependent on parents for longer periods than male offspring from these hatch orders. Together with previous studies this result indicates that even in markedly dimorphic species, the required investment to raise the larger sex is likely to be less than that predicted by body size differences alone. Moreover, among last-hatched nestlings, both sexes faced a reduced food allocation and suffered a slower growth rate and thus final body size, with a concurrent increased probability of mortality. For lasthatched females the reduction in food allocation was more marked, with complete mortality of all last-hatched female nestlings monitored in this study. Once independent, males of any size but only larger females are likely to be recruited into the breeding population. The sex-biased food allocation among last-hatched offspring favoring males thus reflects the relative returns to parents in raising a small member of each sex. Key words: avian growth rates, avian nutrition, nestling food requirements, sex allocation, sex-biased provisioning, sexual size dimorphism. [Behav Ecol]

Consequences of La Niña phase of ENSO for the survival and growth of nestling Burrowing Parrots on the Atlantic coast of South America

Birds are sensitive to perturbations in climate. Changes in reproductive ecology may reflect changes in food availability caused by environmental conditions. We studied the influence of the La Niña phase of the El Niño Southern Oscillation (ENSO) on breeding success and survival and growth of nestling Burrowing Parrots (Cyanoliseus patagonus) (Aves, Psittaciformes) in Patagonia. During the breeding season 1998–99, a severe drought affected the region as a consequence of a strong La Niña. We compare data from a La Niña event with an average year. Clutch sizes were similar in the two years. In both years, clutch size declined during the season. Our results suggest that environmental conditions are not the primary determinant of clutch size in Burrowing Parrots, and seasonal differences are more likely caused by differences in adult quality. Nestling mortality was higher during La Niña, while the surviving nestlings showed reduced growth. Hatching order had a stronger influence on growth and survival of nestlings during La Niña than during the average year. Last-hatched nestlings always showed reduced growth compared with middle-and first-hatched nestlings, but the difference between nestlings was greater during La Niña.

Why is brood reduction in Florida scrub-jays higher in suburban than in wildland habitats?

In a population of Florida scrub-jays, Aphelocoma coerulescens (Bosc, 1795), in a suburban scrub habitat, partial brood loss is much more common (averaging about 30% of nestlings from successful nests) than in a natural habitat (averaging about 5%). We hypothesized that this partial brood loss was attributable to starvation of last-hatched nestlings (i.e., brood reduction), and that large differences in partial brood loss were caused by differences in arthropod food abundance between the two sites. To test these hypotheses, we closely monitored nests in suburban scrub in 1999 and performed arthropod surveys and focal-nest observations in both habitats in 1998 and 1999. In suburban scrub, later hatched nestlings were three times more likely to die before fledging than earlier hatched nestlings, suggesting that brood reduction occurred. In both years, arthropod abundance in the suburban scrub was less than half that of the natural scrub. However, patterns of food delivery by parents were not significantly different between sites, suggesting that lower food abundance does not in itself explain higher partial brood loss in suburban habitat. Differences in the number of helpers, a greater degree of hatching asynchrony or the delivery of lower quality food throughout the nestling period may increase the probability that later hatched nestlings starve in suburban scrub.

Maternally derived yolk testosterone enhances the development of the hatching muscle in the red-winged blackbird Agelaius phoeniceus.

Hatching asynchrony in avian species often leads to the formation of a size hierarchy that places last-hatched nestlings at a significant disadvantage. The hatching muscle (musculus complexus) is responsible for breaking the shell during hatching and for dorsal flexion of the neck during begging. An increase in its strength in last-hatched nestlings could mitigate the effects of hatching asynchrony by reducing the time required for hatching or enhancing the effectiveness of begging for parentally delivered food or both. We have previously found that yolk testosterone concentration increases with laying order in the red-winged blackbird Agelaius phoeniceus. In this study, we investigated the hypothesis that yolk testosterone has anabolic effects on the development of the complexus, thereby influencing competition among asynchronously hatched nestlings. We found that both yolk testosterone concentration and relative complexus mass (complexus mass/nestling body mass) increased with laying order and that these two variables were positively correlated in both newly hatched nestlings and in two-day-old broods. Moreover, direct injections of testosterone into egg yolks resulted in an increase in relative complexus mass, while injections of flutamide, a testosterone antagonist, resulted in a decrease in relative complexus mass. Neither yolk testosterone concentration nor relative complexus mass differed between male and female nestlings.

An Experimental Study of Brood Reduction and Hatching Asynchrony in Yellow Warblers

The purpose of this study was to examine Lack's (1947, 1954) brood-reduction hypothesis concerning hatching asynchrony, and its importance in explaining the evolution of hatching asynchrony in Yellow Warblers (Dendroica petechia). The study was conducted during the summers of 1988-1990 on a population of Yellow Warblers breeding in the dune-ridge forest at Delta Marsh, Manitoba, Canada (58011'N, 98?19'W). I examined the brood-reduction hypothesis experimentally by inducing a sample of females to delay incubation until clutch completion. This was achieved by removing eggs as they were laid, and placing them in a cooler at 200C until clutch completion. As a result, eggs in each manipulated clutch hatched synchronously (hatch spread between firstand last-hatched nestling ?24 hr). Subsequently, I compared the fledging mass and survival rate of nestlings in asynchronously (unmanipulated broods, hatch spread > 24 hr) and synchronously (manipulated) hatching broods. Consistent with the hypothesis, nestling mortality was concentrated in last-hatched nestlings in asynchronous broods and random with respect to hatch order in synchronous broods. Also in agreement with the hypothesis, fledging mass and survival rates of first-hatched chicks were generally higher in asynchronous broods. However, contrary to the hypothesis, fledging mass and survival rates were similar for lasthatched chicks in asynchronous and synchronous broods. Also consistent with the hypothesis, fledging success (no. fledged/clutch) in broods of five tended to be higher in asynchronously hatched broods, regardless of food availability. Finally, fledging rate (no. fledged/no. hatched) was significantly greater in asynchronous broods (four and five nestlings combined) when compared to synchronous broods, especially when food was limiting.

Egg-size variation in Yellow Warblers: apportionment of parental investment and the brood-survival hypothesis

It has been hypothesized that in passerine birds the larger size of last-laid eggs is part of a brood-survival strategy. We examined the usefulness of the brood-survival hypothesis in explaining intraclutch variation in egg mass of Yellow Warblers (Dendroica petechia). In 4- and 5-egg clutches, egg mass increased significantly with laying order. Although last-hatched nestlings in broods of 4 had higher survival rates than their counterparts in broods of 5, there were no differences in the absolute or relative mass of last-laid eggs in clutches of 4 and 5 eggs. In addition, the mass of last-laid eggs that hatched but did not produce a fledgling was not significantly different from that of last-laid eggs that did produce a fledgling. Finally, the relative mass of last-laid eggs was also not correlated with hatch spread or with date of clutch initiation. The results of this study do not support the brood-survival hypothesis.

A Revision of Lack's Brood Reduction Hypothesis

A recent review by T. Amundsen and J. N. Stokland showed that, when food was plentiful, last-hatched nestlings of asynchronously hatched broods died more frequently than their nestmates or nestlings in synchronously hatched broods. They argued that if last-hatched nestlings die as a consequence of hatching asynchrony, then brood reduction must be maladaptive. I construct a model similar to a model by D. M. Temme and E. Charnov. In my model, asynchronously hatched broods experience reduced survival rates of the last-hatched nestling during good food years, and synchronously hatched broods experience entire brood starvation during bad food years. I compare the reproductive performance of parents raising an asynchronously hatched brood to parents raising a synchronously hatched brood. I show that hatching asynchrony is favored over synchronous hatching when good food years are not very frequent, when the survival rate of last-hatched nestlings during good food years is high, when the survival rate of nestlings raised in synchronously hatched broods during bad food years is low, or when bad food years are not severe. I discuss the model's assumptions and predictions, and I compare the results of this model to Temme and Charnov's model.

Motives for Parental Infanticide in White Storks Ciconia ciconia

~.,i' , larger broods and laid larger clutches than non-infanticidal birds. Males killed the p,~, chick in 8 out of 9 cases. Victims were bom from the last-hatched egg in 4- and 5-egg .clutches, they were the lightest in their brood and grew at lower rates than their nestmates during the days preceding their elimination. The last-hatched nestlings in 4-chick broods had lower pre-fledging survival rates than their elder sibs. Potential victims contributed a low fraction to parents' reproductive output, and 4-chick broods were especially costly to raise because parents provisioned them both more frequently and for longer nestling periods. Hence, the presence of an extra chick seems to lower the benefit/cost ratio to parents rearing a large brood once its elder siblings have hatched successfully. If nestlings do not compete aggressively for food, parents would be selected to eliminate the extra chick themselves. This hypothesis could provide an explanation for the existence of parental infanticide algo in other species.

An Experimental Test of the Brood-Reduction Hypothesis in European Starlings

An Experimental Test of the Brood-Reduction Hypothesis in European Starlings