Factors influencing double brooding in Eurasian Hoopoes Upupa epops

Double brooding may be a good strategy for short‐lived species to maximize annual and lifetime reproductive success (ARS and LRS, respectively). Nevertheless, there is typically individual variation in the probability of producing a second clutch. Here we evaluate factors that influence the decision to double brood in the Eurasian Hoopoe Upupa epops. Analyses of an 11‐year dataset showed that 36% of the females and 21% of the males produced a second clutch after successfully raising a first clutch. Double‐brooded females had higher ARS (9.1 ± 1.9 fledglings; mean ± se) and LRS (0.93 ± 0.08 recruits) than single‐brooded females (ARS: 4.5 ± 2.1 fledglings; LRS: 0.36 ± 0.03 recruits). This suggests that double brooding is adaptive in Hoopoes, and raises the question of why most individuals only produce one clutch per season. The probability of double brooding varied only slightly between years, suggesting that it is influenced by individual characteristics rather than by external, population‐level environmental factors. In both sexes, the probability of double brooding increased with earlier timing of the first clutch, and the timing of reproduction was the most important factor influencing reproductive success. The latter is likely to be mediated by changes in resources during the season. The probability of double brooding also increased slightly with female age, due to differences in intrinsic quality among females rather than to a gain in experience. In contrast to many other studies, the probability of double brooding increased with an increasing number of fledglings from the first clutch, suggesting that it is a strategy of individuals of high quality. Taken together, we show that the individual quality of the breeder and the timing of their first clutches are key factors influencing the decision to double brood, and thereby that they are important determinants of reproductive performance in Eurasian Hoopoes.     

Females compensate for moult‐associated male nest desertion in Hooded Warblers

Uniparental offspring desertion occurs in a wide variety of avian taxa and usually reflects sexual conflict over parental care. In many species, desertion yields immediate reproductive benefits for deserters if they can re‐mate and breed again during the same nesting season; in such cases desertion may be selectively advantageous even if it significantly reduces the fitness of the current brood. However, in many other species, parents desert late‐season offspring when opportunities to re‐nest are absent. In these cases, any reproductive benefits of desertion are delayed, and desertion is unlikely to be advantageous unless the deserted parent can compensate for the loss of its partner and minimize costs to the current brood. We tested this parental compensation hypothesis in Hooded Warblers Setophaga citrina, a species in which males regularly desert late‐season nestlings and fledglings during moult. Females from deserted nests effectively doubled their provisioning efforts, and nestlings from deserted nests received just as much food, gained mass at the same rate, and were no more likely to die from either complete nest predation or brood reduction as young from biparental nests. The female provisioning response, however, was significantly related to nestling age; females undercompensated for male desertion when the nestlings were young, but overcompensated as nestlings approached fledging age, probably because of time constraints that brooding imposed on females with young nestlings. Overall, our results indicate that female Hooded Warblers completely compensate for male moult‐associated nest desertion, and that deserting males pay no reproductive cost for desertion, at least up to the point of fledging. Along with other studies, our findings support the general conclusion that late‐season offspring desertion is likely to evolve only when parental compensation by the deserted partner can minimize costs to the current brood.     

Age‐specific responses to spring temperature in a migratory songbird: older females attempt more broods in warmer springs

Increasing global temperature has led to an interest in plasticity in the timing of annual events; however, little is known about the demographic consequences of changing phenology. Annual reproductive success varies significantly among individuals within a population, and some of that variation has to do with the number of broods attempted by reproducing adults. In birds, female age and the timing of reproduction are often predictors of multiple breeding. We hypothesize that double brooding rates may be affected by spring temperature and that the response may vary with female age. We used a long‐term reproductive data set for a migratory songbird, the prothonotary warbler (Protonotaria citrea) to assess which factors influence (a) an individual female's probability of double brooding and (b) the annual variation in population‐level double brooding rates. We found that older and earlier nesting birds are more likely to double brood, and that there is no evidence for senescence with regard to this trait such that the oldest females were most likely to double brood. Previous experience with double brooding (i.e., whether the female double brooded in the previous year) significantly increased the probability of doing so again. When assessing annual variation in the double brooding rate, we found an interaction between spring temperature and the proportion of older females in the population. Specifically, older females are more likely to double brood in years with warmer springs, but this relationship was not seen for younger females. Previous studies have shown that warmer temperatures lead to earlier and narrower peaks in resources and we hypothesize that these peaks are more available to older and earlier arriving females, enabling them to successfully raise more than one brood in a season. Understanding how different age classes respond to changing environmental conditions will be imperative to managing declining species.     

Interspecific offspring killing in owls

In Baranya County (Southern Hungary), tawny owls (Strix aluco) and barn owls (Tyto alba) sequentially use the same nest boxes in a significant number of cases. A total of 460 broods were observed between 1996 and 2003 and, in 12 cases, whole broods of dead tawny owl chicks were registered that had apparently been killed. On investigating the reproductive life characteristics, population sizes, and frequency of killing in these two species, it was concluded that: (1) with growing barn owl population, the number of sequential broods increases but changes in tawny owl population size have no effect on the frequency of sequential broods; (2) the number of killings depends on the number of sequential broods; and (3) with growing barn owl population, the number of killings also grows and this change is unaffected by the size of the tawny owl population. However, no killing occurs as long as 50–60% of the nest boxes are unoccupied. There is no killing either until the percentage of nest boxes occupied by barn owls reaches 40%, although a threshold value like this cannot be shown for the tawny owl. In the cases when a barn owl breeding follows the tawny owl's, the percentage of killing is significantly higher compared to that when barn owls do not breed in the same box. These results indicate that barn owls kill the offspring of tawny owls. By these means, they obtain a breeding place earlier than without killing the chicks of the other species, and this results in higher reproductive success. © 2008 The Linnean Society of London, Biological Journal of the Linnean Society, 2008, 95 , 488–494.     

Multiple Paternity in Polyandrous Barn Owls (Tyto alba)

In polyandrous species females produce successive clutches with several males. Female barn owls (Tyto alba) often desert their offspring and mate to produce a 2^nd annual brood with a second male. We tested whether copulating during chick rearing at the 1^st annual brood increases the male''s likelihood to obtain paternity at the 2^nd annual breeding attempt of his female mate in case she deserts their brood to produce a second brood with a different male. Using molecular paternity analyses we found that 2 out of 26 (8%) second annual broods of deserting females contained in total 6 extra-pair young out of 15 nestlings. These young were all sired by the male with whom the female had produced the 1^st annual brood. In contrast, none of the 49 1^st annual breeding attempts (219 offspring) and of the 20 2^nd annual breeding attempts (93 offspring) of non-deserting females contained extra-pair young. We suggest that female desertion can select male counter-strategies to increase paternity and hence individual fitness. Alternatively, females may copulate with the 1^st male to derive genetic benefits, since he is usually of higher quality than the 2^nd male which is commonly a yearling individual.     

Factors affecting the probability of double brooding by Southern House Wrens

Seasonal fecundity of birds is influenced by clutch sizes and the number of successful breeding attempts during a breeding season. As such, understanding the factors that determine the decision to initiate multiple broods within a season and the consequences of this reproductive tactic is important. We examined the frequency of double brooding by Southern House Wrens (Troglodytes aedon musculus) in eastern Argentina. We analyzed inter‐ and intraseasonal variation in double brooding and evaluated the effect of weather conditions and laying date on the frequency and occurrence of this behavior. Finally, we assessed the effect of double brooding on the seasonal and lifetime productivity of female Southern House Wrens. During our 8‐year study, we found that ～43% (range = 17–83% each year) of breeding pairs attempted a second brood after successfully raising a first brood. The probability of females having a second brood was affected by the laying date of the first nesting attempt, but was independent of the number of young fledged. About 65% of females that started laying eggs before the first quarter of each breeding season produced a second brood, and this percentage decreased to ～40% after this period. In addition, variation in double‐brooding frequency among years was related to weather conditions, with the proportion of pairs double brooding increasing with increased precipitation early in the breeding season. More precipitation likely contributed to an increase in insect abundance. Although double brooding increased the seasonal and lifetime productivity of female Southern House Wrens, additional study of the survival and fate of fledglings from first and second broods is needed to assess the importance of multi‐brooding in the reproductive success of these wrens.     

Egg mass destroying behaviour of the female giant water bugLethocerus deyrollei Vuillefroy (Heteroptera: Belostomatidae)

After being laid on emergent aquatic vegetation, the egg masses ofLethocerus deyrollei are brooded by the male. In laboratory studies, females were observed to destroy egg masses and ingest the fluid of eggs. Brooding males fought with these attackers at first, but then gave up the defense and mated with them. After destroying the egg masses, females laid new ones at the same sites on the same night or the following one, and males brooded the new offspring. The population density of this species is very low. Most males engage in brooding and cease to become acceptable mates after most of the females lay the first egg masses. It is costly for females to search out free males in the aquatic vegetation. By destroying egg masses, however, individual females can gain new mates with little exertion and can make them brood their own offspring. Furthermore, the survival of their own offspring increases with the elimination of their competitors.     

Telomere length in relation to colour polymorphism across life stages in the tawny owl

Telomere erosion has been proposed to be tightly associated with senescence, environmental stressors and life history trade‐offs. How telomere dynamics vary across life stages and especially in relation to (heritable) phenotypic traits is still unclear. The tawny owl Strix aluco display a highly heritable melanin‐based colour polymorphism, a grey and a brown morph, linked to several fitness traits including morph‐specific telomere dynamics. As adults, brown tawny owls have shorter relative telomere length (RTL) and exhibit faster telomere shortening rate than grey owls. Here we test if these morph‐specific telomere dynamics emerge already during growth, or if they are induced only in adult life through differential physiological costs associated with the life history of the morphs. We analysed RTL from 287 tawny owl offspring and 81 first breeding adults to evaluate at what life stage morph‐specific patterns emerge. We found no differences in RTL between the two morphs during the nestling period nor at the first breeding attempt. Sex, brood size or size rank in the nest did not affect offspring RTL. Among first‐breeders, females had shorter telomeres than males suggesting a sampling‐time dependent difference in reproductive costs between sexes, due to the prominent sex roles in tawny owls in the early nestling period. The probability to return to breed after the first breeding attempt was not affected by RTL, sex or colour morph. The lack of morph‐specific difference in RTL among nestlings and first breeders suggests that previously observed morph‐specific differences in RTL dynamics in adults emerge at the onset of the breeding career and is likely due to different physiological profiles and life‐history strategies adopted by adults. We conclude that different telomere dynamics and senescence patterns among highly heritable phenotypes (colour morphs) are likely to be a result of differential costs of reproduction and self‐maintenance.     

An experimental analysis of joint nesting in the salamander Hemidaetylium scutatum (Caudata: Plethodontidae): the effects of population density

Three nesting behaviour patterns are documented in the plethodontid salamander Hemidactylium scutatum. A female may lay eggs (1) in a solitary nest and brood them, (2) in a joint nest and brood them as well as eggs of other females, or (3) in a joint nest that is brooded by another female. The hypothesis that population density was positively associated with joint nesting was tested by following two populations for 5 years and by experimentally manipulating the population density of nesting females in artificial habitats for the latter 2 years. The proportion of joint nests did not vary with density, although joint nests tended to contain eggs of more females at the high population density. Joint nests were usually brooded by one female; thus, most females that laid eggs in joint nests did not brood them at high density. The reproductive success, as measured by survival of embryos, of solitary and joint nesters was equivalent. Joint nests were deserted less often, however, which decreased the probability of catastrophic mortality. The number of days of brooding was significantly positively correlated with loss of body mass of females, suggesting a cost to brooding behaviour. Joint nesting with solitary brooding is not explained by aggressive usurpation of nests or by brood parasitism.     

Parental care and social mating system in the Lesser Spotted Woodpecker Dendrocopos minor

The sexes’ share in parental care and the social mating system in a marked population of the single‐brooded Lesser Spotted Woodpecker Dendrocopos minor were studied in 17 woodpecker territories in southern Sweden during 10 years. The birds showed a very strong mate fidelity between years; the divorce rate was 3.4%. In monogamous pairs, the male provided more parental care than the female. The male did most of the nest building and all incubation and brooding at night. Daytime incubation and brooding were shared equally by the sexes, and biparental care at these early breeding stages is probably necessary for successful breeding. In 42% of the nests, however, though still alive the female deserted the brood the last week of the nestling period, whereas the male invariably fed until fledging and fully compensated for the absent female. Post‐fledging care could not be quantified, but was likely shared by both parents. Females who ceased feeding at the late nestling stage resumed care after fledging. We argue that the high premium on breeding with the same mate for consecutive years and the overall lower survival of females have shaped this male‐biased organisation of parental care. In the six years with best data, most social matings were monogamous, but 8.5% of the females (N=59) exhibited simultaneous multi‐nest (classical) polyandry and 2.9% of the males (N=68) exhibited multi‐nest polygyny. Polyandrous females raised 39% more young than monogamous pairs. These females invested equal amounts of parental care at all their nests, but their investment at each nest was lower than that of monogamous females. The polyandrously mated males fully compensated for this lower female investment. Polygynous males invested mainly in their primary nest and appeared to be less successful than polyandrous females. Polyandry and polygyny occurred only when the population sex ratio was biased, and due to strong intra‐sexual competition this is likely a prerequisite for polygamous mating in Lesser Spotted Woodpeckers.     

The social system of the Pale Chanting Goshawk Melierax canorus; monogamy v polyandry and delayed dispersal

The social organization and reproductive strategy of the Pale Chanting Goshawk Melierax canorus were investigated in four southern African study areas. Territories supporting adults additional to the breeding pair were observed in two study areas. Within one of these areas, these additional adults were either non-breeders staying in their natal territory but actively excluded from the nesting area during the breeding season or a male cobreeder participating fully in reproductive activities with the breeding pair. Polyandrous trios were, however, observed in only one vegetation type in this area, Broken Veld. The annual number of offspring fledged per group did not differ significantly between vegetation types nor between polyandrous trios and monogamous pairs within Broken Veld. Pale Chanting Goshawks lay predominantly two-egg clutches. In 2 out of 5 years, breeding groups succeeded in laying, hatching and even fledging a second brood of young after successfully fledging their first brood. Double brooding occurred more frequently in Broken Veld and most frequently in polyandrous trios in this vegetation type. To accommodate their relatively long breeding cycle (>115 days) in this temperate study area with its limiting summer breeding period, double-brooding Pale Chanting Goshawks laid the first clutch in midwinter and the second, on average, 24 days after the offspring from the first brood left the nest.     

Factors determining the frequency and productivity of double brooding of Barn Owls Tyto alba

Capsule: Early nesting Barn Owls Tyto alba and those that switched nest sites fledged most chicks overall because they could fit two, more productive, nesting attempts into a breeding season.

Aims: To determine the frequency and productivity of double broods in Barn Owls, and for double brooders, to determine what affects the probability of nest switching and how that affects productivity.

Methods: We monitored the first egg date of each nesting attempt, whether it was in a ‘vole year’, whether a breeding attempt was first or a second annual attempt, the number of chicks fledged from each attempt, and whether a pair switched nest sites, if breeding twice, from 602 Barn Owl breeding attempts in an area of lowland England from 1996 to 2007. General linear models were used to determine predictors of the probability that a pair had a second brood and the number of chicks fledged in each nesting attempt, and then for those owls that double brooded, which variables best predicted the probability of switching, and the number of chicks fledged from the second nest. Finally, we tested whether switching resulted in a shorter laying interval and higher annual productivity.

Results: Early nesting birds were more likely to double brood, although this was relaxed in vole years when later nesting birds also double brooded. Productivity (through increased numbers of chicks fledged or reduced chick loss) was higher the earlier a nest occurred, and there were more chicks fledged in good vole years and in second nesting attempts. Productivity, brood depletion, first clutch date and vole years did not determine whether a double brooding pair switched nesting sites. Productivity in the second nest did not change with a switch but productivity increased for early first nests and second nests with a shorter interval between the first and second nest. Switching however decreased nesting interval and nesting interval was also shorter if there were fewer fledglings from the first nest. Overall productivity was higher for pairs that switched.

Conclusions: Double brooding in Barn Owls increased seasonal productivity substantially and its occurrence depended on vole abundance or early nesting. Nest switching between broods may be a strategy for earlier laying of the second brood. Provision of alternative nest sites, close together in a Barn Owl’s home range, may allow earlier re-nesting and so increase productivity.     

Roadway mortality of barn owls in Idaho,USA

We examined the temporal, spatial, and demographic factors that influenced roadway mortality of barn owls (Tyto alba) along a 248-km stretch of Interstate 84 in southern Idaho using systematic road surveys. Counts of dead animals from surveys can be underestimated because of sampling biases; therefore, we also conducted experiments to assess the effects of search and removal bias on the estimates of roadway mortality of owls. We conducted surveys every 2 weeks over a 2-year period and detected 812 dead barn owls (unadjusted mortality rate of 1.64 owls/km/yr). After adjusting this estimate for search and removal bias, we documented mortality rates of up to 5.99 owls/km/year. Owl mortality was not random in relation to sex, age class, or location along the highway. Females and juveniles, which represent individuals more likely to disperse long distances, were killed more frequently than males and adults. During the nonbreeding season, owls were killed more often near agricultural lands than in shrub-steppe, but this pattern was not apparent during the breeding season. Owls were also killed more often on portions of the roadway closer to the Snake River canyon, perhaps because of the availability of nest and roost sites. Mortality rates differed markedly between the 2 years of study, which could have been related to variability in weather and its subsequent effect on owl productivity. Our data suggest that barn owls in this region may not persist under this level of mortality without significant immigration or management. Thus, roadway management to reduce or prevent owl use of roadways, reduce rodent populations near major roads, alert motorists to the presence of owls, or otherwise reduce the chances that vehicles and owls collide would improve barn owl survival and population persistence. © 2012 The Wildlife Society.     

Brood desertion in Kentish Plover Charadrius alexandrinus: an experimental test of parental quality and remating opportunities

Uniparental male care combined with polyandry is rare in birds, and the best known examples are in shorebirds Charadrii. There are two current hypotheses explaining why males care for the brood, whereas females desert and remate: either males are more capable than females at providing uniparental care (“parental quality hypothesis”) or females gain a greater increase in reproductive success by deserting than do males (“remating opportunity hypothesis”). I experimentally tested both hypotheses in Kentish Plover Charadrius alexandrinus, one of the few avian species in which either parent may desert the brood. By experimentally removing one parent when the chicks hatched, I found that male-tended broods had better survival than female-tended ones, particularly up to 6 days after hatching. It is unlikely that differential brood mortality was caused by chilling of the chicks, since the brooding behaviour of males and females was not different. The results of this study are consistent with the explanation that male-tended broods survived better because males were better able to protect the brood from attacks by conspecifics and predators. The remating opportunity hypothesis was also corroborated because single females acquired new mates faster than did single males. The results of this study suggest that both the better parental capability of males and the greater remating opportunities of females predispose Kentish Plovers for uniparental male care, desertion by the female parent and sequential polyandry.     

Parental care trade‐offs in the inter‐brood phase in Barn Swallows Hirundo rustica

In seasonal environments with limited time and energy resources, double‐brooded birds face trade‐offs in the timing of their two reproductive attempts and in the effort allocated to the first and the second broods. In the Barn Swallow Hirundo rustica a long care period for the first brood enhances the survival of first‐brood chicks, but also delays the start of the second brood, which in turn reduces the survival prospects of second‐brood chicks. Probably as a response to this trade‐off, double‐brooded Barn Swallows reduce the period of post‐fledging care for first‐brood fledglings. By radiotracking whole families, we investigated the determinants of this behaviour and its consequences for the survival of the first‐brood fledglings. The end of the females’ investment in post‐fledging care of the first brood was related to the beginning of egg synthesis for the second clutch. With the start of egg synthesis, females significantly reduced provisioning rates to the first‐brood fledglings to less than one‐fifth of the previous rates, while the proportion of time they spent foraging remained high. Assuming that the females’ foraging success was constant, we conclude that their energy income was allocated to egg production rather than fledgling provision. Males did not compensate for the females’ reduced feeding rates. Thus the start of egg production for the second clutch had a marked effect on the quantity of food received by first‐brood fledglings. In parallel with the changes in parental behaviour and provisioning rates, we observed a marked drop in the daily survival rate of first‐brood chicks. These results support the hypothesis that females face a strong trade‐off in the allocation of energy to subsequent broods. Energy allocation to a second clutch involves a cost in terms of reduced provisioning, and as a result the survival of first‐brood chicks is compromised. This is probably outweighed by the improved success of an early second brood.     

Reproductive seasonality of the seaweed pipefish Syngnathus schlegeli (Syngnathidae) in the Seto Inland Sea, Japan

Latitudinal variations in fitness-related traits have been reported in a variety of organisms. Intraspecific comparison of such traits among populations living under different environmental conditions is an effective approach for elucidating the cause and consequences of such latitudinal variations. In the present study, population demography, seasonal changes in somatic and reproductive conditions, and the occurrence of egg-brooding males were investigated in the seaweed pipefish, Syngnathus schlegeli, collected monthly in the Seto Inland Sea, Japan, in order to estimate the reproductive season and mating pattern. The findings were then compared with those reported for a population in Otsuchi Bay, northern Japan. We found that the reproductive season is longer in the Seto Inland Sea population (March–November) than in the Otsuchi Bay population (May–October), although reproductive activity may temporarily cease during August in the Seto Inland Sea population. Males of the Seto Inland Sea population brooded eggs that were at the same developmental stage, suggesting that males mate with only one female in a single brooding episode (i.e., monogamy)—in contrast to the Otsuchi Bay population, where a portion of males brooded eggs consisting of multiple clutches at different developmental stages, suggesting that multiple females contribute to a single brood (i.e., polygamy). Additionally, we found that the standard lengths of both males and females are approximately 30?mm smaller in the Seto Inland Sea than in the Otsuchi Bay population. These results suggest that the multiple mating by males in a single brood and the larger body size in the Otsuchi Bay population are results of fecundity selection on life history and behavioral traits to adapt to the shorter reproductive season and lower reproductive efficiency in this relatively cold environment.     

FEMALE REPRODUCTIVE EFFORT DEPENDS ON THE DEGREE OF ORNAMENTATION OF THEIR MATES

Sexual selection theory assumes that secondary sexual characters do not influence female reproductive effort. Female animals may invest relatively more in reproduction if they acquire mates of high phenotypic quality, because offspring sired by preferred males may be relatively more viable than offspring sired by less preferred males. Here we report for the first time in a field study that females of the monogamous barn swallow Hirundo rustica adjust their reproductive effort to the attractiveness of their mates. Experimental manipulation of male tail length, which is a trait currently subject to a directional female mating preference, affected the reproductive effort by females in single broods as well as their decision on the seasonal number of clutches. These results, and those of previous experiments, demonstrate that female barn swallows assess the quality of their mates throughout the reproductive season and adjust their reproductive decisions accordingly. This result has important implications for the theory of sexual selection and for the possibility of testing current models of female mate preferences, because the viability of offspring will be confounded by differential reproductive effort.     

Sexual selection in the monogamous barn swallow (Hirundo rustica). II. Mechanisms of sexual selection

Mechanisms of sexual selection in the monogamous, sexually dimorphic barn swallow (Hirundo rustica) were studied during a seven-year period. First, the sex ratio of reproducing adults was male-biased, and mated males had significantly longer tail ornaments than unmated males. Secondly, some of the unmated individuals later committed infanticide and became mated with the mother of the killed brood. Fathers of killed broods had significantly shorter tails than other males, and there was a tendency for infanticidal males to have longer tail ornaments than other unmated males. Thirdly, long-tailed male barn swallows were more successful in acquiring extra-pair copulations than other males, and females involved in extra-pair copulations, as compared to females not involved in such copulations, had mates with shorter tail ornaments. Fourthly, male barn swallows having long tails as compared to short-tailed males acquired mates in better body condition. Females mated to long-tailed males reproduced earlier, laid more eggs and were more likely to have two clutches than were females mated to short-tailed males. Finally, females mated to long-tailed males put more effort into reproduction than did other females, as evidenced by their relatively larger contribution to feeding of offspring. Thus, at least five different components of sexual selection affected male reproductive success. Selection arising from differential success during extra-pair copulations, differential reproductive success and differential male reproductive effort thus accounted for most of the selection on tail ornaments in male barn swallows.     

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.