Hatching order affects offspring growth,survival and adult dominance in the joint‐laying Pukeko Porphyrio melanotus melanotus

In birds with asynchronous hatching, hatching order is an important factor in determining offspring phenotype. Many previous studies have demonstrated that later‐hatched offspring show reduced growth and survival during development. However, few studies have followed individuals from hatching to adulthood to test whether the effects of hatching order persist into later life. Here, we explore patterns of hatching order and fitness‐related traits in the Pukeko Porphyrio melanotus melanotus, a cooperatively breeding bird that lives in stable social groups that form linear dominance hierarchies. Pukeko groups sometimes contain two breeding females that lay eggs in the same nest (joint‐laying). Thus, competition between nest‐mates can influence the relative fitness of each laying female. We show that in both single‐clutch and joint‐clutch nests, earlier‐hatched Pukeko chicks grow faster and survive better than later‐hatched brood‐mates. Moreover, earlier‐hatched chicks achieve higher dominance ranks as adults, making this study one of the first to find a relationship between hatching order and adult dominance in wild birds. Finally, we show that in groups with two breeding females, the chicks of the primary female hatch earlier than the chicks of the secondary female. As a result, the offspring of the primary female may be at a competitive advantage, which could have important implications for social dynamics in this species.     

Parental care in Semipalmated Sandpipers Calidris pusilla: brood desertion by females

Although Semipalmated Sandpipers Calidris pusilla are monogamous, with biparental incubation, most females (86–97%) deserted their broods to the care of their mates, 0–11 days (average 6) after their eggs hatched. Males left the brood an average of 8 days later, shortly before or after the chicks fledged. In several instances, females that deserted in one year remained with the chicks the next year, and vice versa. Females deserted chicks at nests that hatched later in the season at an earlier age than those had hatched earlier ( r ²> o.6). Since females appeared to have an energy deficit in at least some years, and suffered higher mortality rates than males during breeding, it is possible that females deserted broods in order to take advantage of better feeding conditions at migratory stopovers in northeastern North America early in the season. There was little evidence of higher nesting success or earlier hatching date in reuniting pairs, although if both members of a pair returned to the breeding area, 80% reunited. Increased survival of their mate may be most advantageous to males in ensuring that they obtain a female the following year.     

Female survival,lifetime reproductive success and mating status in a passerine bird

In facultatively polygynous birds, secondary females of polygynously mated males typically have reduced annual reproductive success, because polygynous males provide less paternal care than monogamous males. Life history theory predicts that, as a result of increased reproductive investment, secondary females should suffer from reduced survival and lifetime reproductive success, but previous studies provided only weak support for this hypothesis. We used 7 years of data to study the fitness of female collared flycatchers Ficedula albicollis in relation to mating status by estimating survival and lifetime reproductive success. Taking differences in recapture probability into account, a mark-recapture analysis revealed that females observed at least once to breed as secondary female had higher survival than other females. This relationship was not confounded by laying date, because when we assessed the impact of laying date on survival, we found similar survival patterns. Females of polygynous males had reduced breeding success in terms of number of young fledged during the current reproductive event. However, during their lifetime females found at least once in primary or secondary mating status produced significantly more eggs, and at least the same number of fledglings and recruits as monogamous females. Thus, in the collared flycatcher, females of polygynously mated males seem to suffer from mating status during the most recent reproductive event, but considering survival and lifetime reproductive success, the apparently disadvantageous mating event is not necessarily associated with reduced residual reproductive value.     

Mate-sharing costs in polygynous Northern Lapwings Vanellus vanellus

In this study bigamous female Northern Lapwings Vanellus vanellus received significantly less incubation relief from their males than monogamous females. On average, monogamous males spent 34.3% of their time incubating and bigamous males 29.9%. Bigamous males divided their effort between their nests, incubating on average 9.4% on primary nests and 20.5% on secondary nests. Bigamous females compensated for the lack of male relief. Primary females incubated for 71.8% of their time, secondary females for 64.2%, while monogamous females spent 52.7% of their time incubating. As a result, there was no significant difference in total nest attentiveness among nests of different status. Primary and secondary females received equivalent incubation relief from the male. Bigamous males increased their contribution to incubation significantly as the season progressed. A bigamous male's distribution of incubation relief between his females was unrelated to female body mass, or to the degree of asynchrony between primary and secondary females in arrival and laying. Incubation time was significantly, negatively, correlated with total nest attentiveness. Monogamous females spent most time, secondary females spent an intermediate time, and primary females spent the least time on maintenance behaviour (foraging, comfort behaviour, inactivity). No significant differences were found in hatching success among females of different mating status. However, the ratio of unhatched to hatched eggs (i.e. the eggs that remained in the nest at the time of hatching) differed significantly: secondary females hatched a smaller proportion of their eggs than monogamous and primary females.     

Polygyny and its fitness consequences for primary and secondary female pied flycatchers

In polygynous species with biparental care, the amount of paternal support often varies considerably. In the pied flycatcher (Ficedula hypoleuca), females mated with monogamous males receive more male assistance during the nestling phase than females mated with bigynous males, as the latter have to share their mates with another female. Bigynous males, however, give more support to their primary broods than to their secondary broods. Using a long-term dataset (31 years), the present study revealed that direct reproductive success, i.e. number of fledglings, was lower in females that mated with bigynous males, especially in secondary broods without male assistance, than in females that mated with monogamous males. Secondary broods with male assistance were more affected than primary broods. Female survival was independent of mating status. In primary broods, a delayed compensation for inferior direct reproductive success was found in terms of the number of grandoffspring, a phenomenon that did not occur in secondary broods. Delayed compensation in primary broods refers to indirect effects, i.e. good genes. According to the sexy son hypothesis, genetically superior (i.e. sexy) males may have sons with a higher number of broods belonging to a polygynous breeding status than do sons from broods with a monogamous father. This was indeed the case for sons descending from primary broods, but not for sons descending from secondary broods.     

Annual productivity and individual female reproductive success in a Great Bustard Otis tarda population

The reproductive success of Great Bustards Otis tarda in north-western Spain was studied between 1987 and 1998, both at the population ( c . 700 adult females breeding in our study area) and the individual level (sample of 32 marked females). Overall productivity was low, with a population mean of only 0.14 chicks reared per adult female, and an average breeding success of 0.15 chicks per year in the sample of marked females, but interannual variability was high (0.04–0.29). Population productivity was positively correlated with winter (October–March) precipitation prior to each breeding season, and negatively correlated with the number of days of rain during the hatching period. High annual productivity resulted from a high proportion of females rearing two chicks. Reproductive success was higher in females older than 6 years than in younger birds. The proportion of females in the marked sample that failed in breeding after having bred successfully the previous season was significantly higher than the proportion of those that did not. Finally, females with a higher than average breeding success tended to breed successfully in years of both low and high population productivity, whereas those with lower than average breeding success did so only in years of high productivity.     

Seasonal declines in reproductive success of the common tern Sterna hirundo: timing or parental quality?

Reproductive success declines over the course of the breeding season in many bird species. Two categories of hypothesis have been evoked to explain this decline. The “timing” hypothesis suggests that seasonal declines in breeding success are attributable to the date of laying. The “parental quality” hypothesis suggests that seasonal declines result from the fact that young, inexperienced, or low quality birds breed later in the season. To evaluate the relative importance of timing and parental quality, egg exchanges and removals were used to manipulate hatching dates of common terns Sterna hirundo. Indices of quality, attendance, provisioning rates, and reproductive success of birds in three experimental groups (delayed hatch pairs, advanced hatch pairs, and pairs induced to relay) were compared to those of date‐matched controls. Pairs that hatched chicks early raised more chicks than pairs hatching chicks late in the season, regardless of initial laying date. This suggests that hatching chicks early is advantageous in itself. Our results, however, also support the parental quality hypothesis. There was a significant negative relationship between natural laying date and fledging success, independent of hatching date. Differences in chick growth and survival suggest that higher quality adults may be able to compensate for the disadvantages of late hatching dates and achieve similar reproductive success to that of pairs hatching chicks early. We found that pairs hatching chicks late in the season were subject to more incidents of kleptoparasitism than those hatching chicks early. This may be a proximate factor contributing to seasonal declines in reproductive success for common terns, although such a mechanism would not be likely in non‐colonial species. Failure to control for egg quality may have biased the results of some prior egg exchange experiments. Additionally, altered cost of incubation may be an unavoidable confounding factor in studies designed to manipulate timing of breeding.     

Sex roles, parental effort and offspring desertion in the monogamous Eurasian Curlew Numenius arquata

The reasons for female desertion of offspring and the evolution of predominantly male care among monogamous bird species are not clearly understood. We studied parental effort during the incubation and chick rearing periods in the Eurasian Curlew Numenius arquata in western Finland, and compared timing of brood desertion with other populations in Europe. Males and females contributed equally to incubation and showed no differences in the intensity of mobbing behaviour towards a potential nest predator (stuffed crow) shortly after hatching. However, females deserted their offspring approximately halfway through the brooding period ( c. 16 d after hatching), while males remained with chicks until independence ( c. 35 d). Females with late-laid clutches deserted their offspring sooner after hatching than those with clutches produced earlier in the season. Curlew females deserted younger chicks in northeast Europe, where laying dates were later, breeding seasons shorter and migration distances were longer, than in western and central Europe. We suggest that the most likely reasons for offspring desertion by females may be associated with increased female survivorship and maintenance of pairbond between years.     

Females better face senescence in the wandering albatross

Sex differences in lifespan and aging are widespread among animals. Since investment in current reproduction can have consequences on other life-history traits, the sex with the highest cost of breeding is expected to suffer from an earlier and/or stronger senescence. This has been demonstrated in polygynous species that are highly dimorphic. However in monogamous species where parental investment is similar between sexes, sex-specific differences in aging patterns of life-history traits are expected to be attenuated. Here, we examined sex and age influences on demographic traits in a very long-lived and sexually dimorphic monogamous species, the wandering albatross (Diomedea exulans). We modelled within the same model framework sex-dependent variations in aging for an array of five life-history traits: adult survival, probability of returning to the breeding colony, probability of breeding and two measures of breeding success (hatching and fledging). We show that life-history traits presented contrasted aging patterns according to sex whereas traits were all similar at young ages. Both sexes exhibited actuarial and reproductive senescence, but, as the decrease in breeding success remained similar for males and females, the survival and breeding probabilities of males were significantly more affected than females. We discuss our results in the light of the costs associated to reproduction, age-related pairing and a biased operational sex-ratio in the population leading to a pool of non-breeders of potentially lower quality and therefore more subject to death or breeding abstention. For a monogamous species with similar parental roles, the patterns observed were surprising and when placed in a gradient of observed age/sex-related variations in life-history traits, wandering albatrosses were intermediate between highly dimorphic polygynous and most monogamous species.     

Effects of maternal quality and mating status on female reproductive success in the polygynous spotless starling

Female mating status may affect reproductive success in avian polygynous mating systems through a combination of differences in female parental quality and status-dependent male assistance in parental care. Traditionally the literature has emphasized male assistance, neglecting evidence for consistency in female parental quality independent of mating status or repeatability in status. We studied the effects of male assistance on breeding success and its association with female mating status in a population of the polygynous spotless starling, Sturnus unicolor, during 3 years. Nestling provisioning by males improved the fledging success of late (mostly second) but not early (mostly first) broods. Reproductive success of females was affected mainly by female maternal quality: (1) primary and secondary females did not differ in output for early broods and in seasonal output despite a greater male assistance at primary nests; (2) monogamous females were more successful despite receiving no more help than other females; and (3) primary and secondary females had different clutch sizes before male assistance in parental care could operate. Female mating status was not significantly repeatable within seasons or between years. Females who changed status between years were as successful when rearing broods as secondary females as they were as primary or monogamous females. Breeding success (proportion of eggs resulting in fledglings) and clutch size were significantly repeatable between years for late but not for early clutches. Performance showed no strong association with female age or condition. Female breeding success seems to be weakly affected by male assistance in this sedentary, colonial species, and more dependent on inherent differences between females. Copyright 2002 The Association for the Study of Animal Behaviour. Published by Elsevier Science Ltd. All rights reserved.     

The Impact of Increased Food Availability on Reproduction in a Long-Distance Migratory Songbird: Implications for Environmental Change?

Many populations of migratory songbirds are declining or shifting in distribution. This is likely due to environmental changes that alter factors such as food availability that may have an impact on survival and/or breeding success. We tested the impact of experimentally supplemented food on the breeding success over three years of northern wheatears (Oenanthe oenanthe), a species in decline over much of Europe. The number of offspring fledged over the season was higher for food-supplemented birds than for control birds. The mechanisms for this effect were that food supplementation advanced breeding date, which, together with increased resources, allowed further breeding attempts. While food supplementation did not increase the clutch size, hatching success or number of chicks fledged per breeding attempt, it did increase chick size in one year of the study. The increased breeding success was greater for males than females; males could attempt to rear simultaneous broods with multiple females as well as attempting second broods, whereas females could only increase their breeding effort via second broods. Multiple brooding is rare in the study population, but this study demonstrates the potential for changes in food availability to affect wheatear breeding productivity, primarily via phenotypic flexibility in the number of breeding attempts. Our results have implications for our understanding of how wheatears may respond to natural changes in food availability due to climate changes or changes in habitat management.     

Descriptive and experimental evidence for timing-mediated polygyny risk in a pied flycatcher Ficedula hypoleuca population

In polygynous species with biparental care, mates are often acquired in succession. Most research has focussed on the cost of polygyny in secondary females, but primary females may also suffer from reduced paternal care. The likelihood of sharing a male may be higher for early laying females, which could counteract the fitness benefits of breeding early. In this study, we use 12 years of data on pied flycatchers Ficedula hypoleuca, to show that the likelihood of becoming a primary female of a polygynous male declines over the season. Moreover, we provide experimental evidence that early breeding elevates polygyny risk, through an experimental manipulation that introduced early breeding females to a population with later breeding phenology. We found that, independently of breeding date, primary females slightly more often experienced complete brood failures than monogamous females, but did not differ in number of fledged offspring among successful broods or number of locally returning recruits. However, apparent survival in subsequent years was substantially lower in primary females, indicating that they may compensate for reduced male care at the expense of future reproduction. Our study reveals that polygyny risk indeed increases with early breeding and entails a local survival cost for primary females. However, this cost is likely largely outweighed by fitness benefits of early breeding in most years. Hence it is unlikely that the increased polygyny risk of early breeding counteracts the fitness benefits, but it may reduce selection for breeding extremely early.     

Breeding systems of New Zealand Snipe Coenocorypha aucklandica and Chatham Island Snipe C. pusilla; are they food limited?

New Zealand Snipe Coenocorypha aucklandica were studied over six breeding seasons on the Snares Islands. The study area (7.5 ha) held about 20 pairs at a density of 3.2 ± O.5 pairs/ha, plus 5 to 25 nonterritorial birds. Most matings were monogamous but simultaneous polygyny was recorded in one territory (by two different males) in four consecutive seasons. Males courtship fed females before egg-laying. The typical clutch was two eggs, laid three days apart. Incubation was shared equally by the sexes in monogamous pairs and took 22 days. Some females with polygynous mates attempted to incubate unaided, which took about 38 days. Broods were split at hatching, with the male caring for the first chick to leave the nest. Chicks were fed by adults for at least 41 days, and did not become independent until about 65 days old. Growth rates were slow compared to Common Snipe Gallinago gallinago and full plumage took about 54 days to attain. No pairs were double-brooded but 43% of pairs that failed during incubation or early chick-rearing renested together. Some breeders of both sexes who had lost their dependent chick bred a second time with a new mate while their first mate continued rearing the surviving chick (sequential polygyny and polyandry). Hatching success was 80%, and fledging success was 48%. Each pair produced, on average, O.6 fledglings per year. Chatham Island Snipe C. pusilla were studied on Rangatira Island during the 1983–84 breeding season. Breeding density was about 5.6 pairs/ha. The breeding system was very similar to that for C. aucklandica but chicks became independent at about 41 days old. Hatching success was 89%. Compared to Common Snipe, Coenocorypha snipes occurred at high densities, had courtship feeding, large eggs, a long interegy interval, a small clutch, shared incubation and a long incubation period. Nest desertion rates were high, but overall hatching success was also high, chick growth rates were slow, there was a long period of chick dependence and a long relaying interval following nest failure or chick loss. Survival rates of both adults and chicks were high. These differences are attributed to the absence of predation, and to intense intraspecific competition for food in a stable environment.     

Costs of large communal clutches for male and female Greater Rheas Rhea americana

The breeding system of the Greater Rhea Rhea americana is almost unique among birds as it combines harem polygyny and sequential polyandry, with communal egg-laying and uniparental male care. In this species, large communal clutches (more than 30 eggs) are rare and have a lower hatching success than smaller clutches. Here we analyse the proximate causes of hatching failures and the costs of large communal clutches (and therefore the costs of extensive polygyny) for males and females. We evaluated if length of the nesting period, egg viability, egg losses during incubation and male parental activity at the nest were affected by clutch size. We also evaluated if chicks hatched from large clutches have a lower survival during the first 2 months after hatching. Large clutches had longer nesting period and lower hatching success, mainly as a result of bacterial contamination of the eggs and increased hatching asynchrony. In addition, large clutches tended to lose more eggs as a result of accidental breakage or predation. Male activity at the nest and chick survival were not related to clutch size. Low hatching success, nest predation risk and energetic costs associated with large clutches penalize females that join large harems and males that accept additional eggs into the nest.     

Experimental evidence for the relationship between food supply, parental effort and chick survival in the Lesser Black-backed Gull Larus fuscus

We studied breeding success, chick growth, parental effort and chick behaviour in two groups of Lesser Black-backed Gulls Larus fuscus whose chicks were provided with additional food until 7 days after hatching or until fledging. These data were compared with those from control pairs which we studied simultaneously to test the hypotheses that food was in short supply during the chick stage at the colony site and that in such circumstances the behaviour of adults and young is mainly responsible for the low success. Pairs whose chicks were fed with additional food until fledging showed a higher fledging success than control pairs (intermediate for pairs of first experimental group). During the first week after hatching, experimental adults of both groups were present together at the territory for longer than control pairs. In adult females of experimental pairs, the length of feeding trips was shorter than in females of control pairs, whilst the rate of chick feeding was more frequent in the experimental broods. After the chicks were 7 days old, differences were significant only for the experimental pairs whose chicks were provided with additional food until fledging. Chicks fed until fledging showed a higher daily mass and wing-length increments and reached a higher fledging mass at an earlier age than both control chicks and chicks which were provided with additional food until day 7. Starvation occurred only in control chicks and in chicks of the first experimental group after we had stopped providing food. When food was in short supply, fledging success of gulls was adversely affected as a result of both starvation (because of the lower feeding rates of chicks) and a higher predation rate (arising from changes in behaviour of both adults and chicks).     

2. SWIFTS AND OTHER BIRDS NESTING IN BUILDINGS

The nesting success of Marabou Storks Leptoptilos crumeniferus breeding in north-eastern Swaziland is closely associated with rainfall, with nests started late in the season exposed to higher rainfall and showing lower success. This may be related to lower food intake and slower growth of the chicks. This study set out to determine whether hatching date and sequence of laying affected the growth rate of chicks. Chicks were also sexed, as Marabou Storks show sexual size dimorphism—males are on average 20% larger—and this trait is often associated with differing patterns of growth between sexes. Nestlings were measured weekly from hatching until they either died or fledged. Nestling development is described in detail and photographs of different-aged chicks are presented. The nestling period was significantly shorter for female chicks, at 94 d, than for male chicks at 104 d. Male and female chicks differed in growth rate and asymptote for both mass and wing length. Unusually, females showed higher instantaneous growth rates for much of the nestling period. Chicks surpassed adult mass before fledging. Date of hatching had an effect on growth rates, with chicks at late nests having slower growth, consistent with a decline in food availability. Marabou Storks appear to be slower growing than expected for the Ciconiidae, the taxonomic family to which they belong.     

Exclusion of ground predators improves Northern Lapwing Vanellus vanellus chick survival

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

The sexy son hypothesis: data from the pied flycatcher Ficedula hypoleuca

The sexy son hypothesis has been proposed as a possible explanation for polygyny in territorial birds. Females mated with polygynous males are assumed to derive benefits in future generations through their ‘sexy’ sons, and hence they can afford to produce fewer offspring than simultaneously breeding monogamous females, the polygyny threshold thus being reduced. In the pied flycatcher, secondary females are not fully aided by males in feeding the nestlings, and they produce only 65% as many fledglings as do simultaneous monogamous and primary females. We have proposed male deception through polyterritoriality as the explanation for females ending up as secondary females, while some authors have advocated the sexy son hypothesis as an alternative. However, secondary females do not achieve benefits in future generations in this species. Repeatability of male mating status is far too low to grant any significant benefits through grandsons. In fact, offspring hatched in secondary female nests suffer from food shortage and therefore are of poor phenotypic quality with low fledging weight and short tarsus length. Therefore they are likely to enjoy lower reproductive success than offspring born in monogamous nests, as is illustrated by data on the relation between lifetime reproductive success and tarsus length. Altogether the applicability of the sexy son hypothesis is limited since it is based on the unrealistic assumption of relatively high heritability for a character with great influence on male fitness.     

Increased lifetime reproductive success of first‐hatched siblings in Common Kestrels Falco tinnunculus

Order of birth has profound consequences on offspring across taxa during development and can have effects on individuals later in life. In birds, differential maternal allocation and investment in their progeny lead to variance in the environmental conditions that offspring experience during growth within the brood. In particular, laying and hatching order have been proposed to influence individual quality during the growing period, but little is known about the fitness consequences that these two factors have for offspring from a lifetime perspective. We explored the effect of laying and hatching order on post‐fledgling survival (measured as recruitment probability) and lifetime reproductive success (LRS) in Common Kestrels Falco tinnunculus, using a long‐term and individual‐based dataset. First‐hatched chicks showed higher survival probability and LRS than their siblings. This effect was not due to body condition of the individuals at adulthood, the quality of their mates or the reproductive outcome compared with later‐hatched individuals. Instead, first‐hatched chicks had a higher recruitment probability. This could be explained by the higher body condition attained by first‐hatched chicks at the end of the nesting period, perhaps due to an enhanced competitive advantage for food over their siblings at the time of hatching. Laying order, in contrast to hatching order, appeared to have little or no effect on LRS. Our results suggest that hatching order within siblings predicts fitness, and that better early‐life conditions during growth experienced by first‐hatched chicks improve first survival and then recruitment, resulting in an enhanced LRS.     

Parental care of the Common Tern Sterna hirundo

Parental care activities of male and female Common Terns Sterna hirundo were recorded over two breeding seasons. Males and females exhibited distinct parental roles throughout a breeding bout. Courtship feeding by males was extensive prior to and during egg-laying, but declined with the onset of incubation. Females performed significantly more incubation behaviour than males although both sexes spent equal time attending at the nest site. During the chick stage, females spent significantly more time on the territory than did males. Chick feeding was largely the responsibility of the male; males fed chicks at a rate approximately three times higher than that of females. In addition, whereas females showed no trend in the size of fish delivered to chicks relative to chick age, the size of fish delivered by males increased with chick age. Courtship feeding activities and extensive chick feeding contributions by male Common Terns appear to outweigh parental contributions by females, contrary to predictions for a monogamous species.