Life-history and ecological correlates of geographic variation in egg and clutch mass among passerine species

Broad geographic patterns in egg and clutch mass are poorly described, and potential causes of variation remain largely unexamined. We describe interspecific variation in avian egg and clutch mass within and among diverse geographic regions and explore hypotheses related to allometry, clutch size, nest predation, adult mortality, and parental care as correlates and possible explanations of variation. We studied 74 species of Passeriformes at four latitudes on three continents: the north temperate United States, tropical Venezuela, subtropical Argentina, and south temperate South Africa. Egg and clutch mass increased with adult body mass in all locations, but differed among locations for the same body mass, demonstrating that egg and clutch mass have evolved to some extent independent of body mass among regions. A major portion of egg mass variation was explained by an inverse relationship with clutch size within and among regions, as predicted by life-history theory. However, clutch size did not explain all geographic differences in egg mass; eggs were smallest in South Africa despite small clutch sizes. These small eggs might be explained by high nest predation rates in South Africa; life-history theory predicts reduced reproductive effort under high risk of offspring mortality. This prediction was supported for clutch mass, which was inversely related to nest predation but not for egg mass. Nevertheless, clutch mass variation was not fully explained by nest predation, possibly reflecting interacting effects of adult mortality. Tests of the possible effects of nest predation on egg mass were compromised by limited power and by counterposing direct and indirect effects. Finally, components of parental investment, defined as effort per offspring, might be expected to positively coevolve. Indeed, egg mass, but not clutch mass, was greater in species that shared incubation by males and females compared with species in which only females incubate eggs. However, egg and clutch mass were not related to effort of parental care as measured by incubation attentiveness. Ecological and life-history correlates of egg and clutch mass variation found here follow from theory, but possible evolutionary causes deserve further study.     

Differential investment and costs during avian incubation determined by individual quality: an experimental study of the common eider (Somateria mollissima)

Individuals of different quality may have different investment strategies, shaping responses to experimental manipulations, thereby rendering the detection of such patterns difficult. However, previous clutch-size manipulation studies have infrequently incorporated individual differences in quality. To examine costs of incubation and reproductive investment in relation to changes in clutch size, we enlarged and reduced natural clutch sizes of four and five eggs by one egg early in the incubation period in female common eiders (Somateria mollissima), a sea duck with an anorectic incubation period. Females that had produced four eggs (lower quality) responded to clutch reductions by deserting the nest more frequently but did not increase incubation effort in response to clutch enlargement, at the cost of reduced hatch success of eggs. Among birds with an original clutch size of five (higher quality), reducing and enlarging clutch size reduced and increased relative body mass loss respectively without affecting hatch success. In common eiders many females abandon their own ducklings to the care of other females. Enlarging five-egg clutches led to increased brood care rate despite the higher effort spent incubating these clutches, indicating that the higher fitness value of a large brood is increasing adult brood investment. This study shows that the ability to respond to clutch-size manipulations depends on original clutch size, reflecting differences in female quality. Females of low quality were reluctant to increase investment at the cost of lower hatch success, whereas females of higher quality apparently have a larger capacity both to increase incubation effort and brood care investment.     

Egg temperature and initial brood patch area determine hatching asynchrony in Magellanic penguin Spheniscus magellanicus

In birds, the adaptive significance of hatching asynchrony has been under debate for many years and the parental effects on hatching asynchrony have been largely assumed but not often tested. Some authors suggest that hatching asynchrony depends on the incubation onset and many factors have been shown to influence hatching asynchrony in different species. Our objective was to analyze the exact timing of the onset of incubation and if this affects hatching asynchrony; and, in addition, which other factors (brood patch development, incubation position, adult body condition, intra‐clutch egg dimorphism, laying date and year) affect hatching asynchrony in Magellanic penguins Spheniscus magellanicus. We first estimated the eggshell temperature at which embryo development starts, with a non‐destructive and novel method. We then recorded individual egg temperatures in 61 nests during incubation, and related them, and other breeding parameters, to hatching asynchrony. We also observed incubation positions in 307 nests. We found a significant positive relationship between hatching asynchrony and the temperature that the first‐laid egg experienced during egg laying and between hatching asynchrony and the initial brood patch area. We also found a negative relationship between hatching asynchrony and the difference in temperature between second and first‐laid eggs within a clutch, measured after the egg‐laying period was finished. We ruled out position of the eggs during incubation, adult body condition, egg volume, laying date, and study year as factors influencing hatching asynchrony. The egg temperature during laying and the difference in temperature between eggs of a clutch are determinants of hatching asynchrony in Magellanic penguins.     

A comparative study of egg mass and clutch size in the Anseriformes

The factors explaining interspecific differences in clutch investment in precocial birds are poorly understood. We investigated how variations in clutch characteristics are related to environmental factors in a comparative study of 151 extant species of ducks, geese and swans (Anseriformes). Egg mass was negatively related to clutch size in a phylogenetic regression, a relationship that was much stronger when controlling for female mass. Nest placement was related to both egg size and clutch size, with cavity-nesting species laying more but smaller eggs. Egg size was positively correlated with incubation period and with female mass, and also with sexual size dimorphism (i.e. male mass relative to that of the female). Clutch size was not related to female mass. Species with long term pair bonds laid smaller clutches and larger eggs. The size of the breeding range was strongly positively correlated with clutch size and clutch mass, and its inclusion in multivariate models made other biogeographical variables (hemisphere, breeding latitude or insularity) non-significant. The small clutches in insular species appear to be a product of small range size rather than insularity per se. Our results suggest there is an evolutionary trade-off between clutch and egg size, and lend support to Lack’s resource-limitation hypothesis for the waterfowl.     

Time-dependent reproductive decisions in the blue tit

Many breeding attempts in birds do not result in any fledged young due to predation on eggs or young. Consequently, the influence of time constraints on reproductive decisions are integrated parts of the reproductive behaviour of birds breeding within short, seasonal climate zones. In this study, I mimicked nest predation by removing blue tit (Parus caeruleus) clutches shortly after completion. Around 75% of the removed clutches were followed by a repeat clutch. Females producing their first clutch early in the season and females with an early onset of incubation in the laying sequence (an indication of high parental or territory quality) were most likely to initiate a repeat clutch. A trade‐off between the benefits of a repeat clutch and survival likely stopped late females in bad condition from investing more in the current reproductive season. Females producing a repeat clutch laid fewer eggs, had an earlier onset of incubation in the laying sequence and produced larger eggs than they did when producing their original first clutch. Eggs produced after the onset of incubation were especially large in the repeat clutches. Since food availability was presumably higher when the female produced her repeat clutch compared with her first clutch, females made a strategical decision when reducing clutch size, whereas onset of incubation and egg size may have been energetically constrained when producing the first clutch. Females that produced a relatively large clutch, had a relatively early onset of incubation, and laid relatively large eggs in their first clutch also did so when producing a repeat clutch, indicating that some of the variation in breeding parameters are due to differences in parental or territory quality. Differences between years in the temperature‐dependent development rate of caterpillars seem to affect the time constraints on breeding. A year with a predicted early seasonal decline in caterpillars resulted in short intervals between removal and relaying, small clutches and an early onset of incubation.     

Reproductive parameters in relation to food supply in the whiskered tern ( Chlidonias hybrida )

It is generally accepted that breeding terns are sensitive to food supply and that their reproductive effort could be substantially affected by the availability and access to resources. In this study we examined reproductive parameters in the whiskered tern Chlidonias hybrida in relation to food supply during the courtship feeding period (food brought by males to females) over a 2-year period (2004–2005). We also studied whether the condition of the nestlings [body condition index (BCI)] was related to a proxy of the reproductive investment of the adults (the clutch size) during a season of food shortage. Behavioural observations showed a decrease in the intensity of male courtship feeding between years (2004 > 2005), and a strong shift in the relative abundance of the two prey groups (invertebrates/fish; invertebrate prey dropped from 88.0 to 49.3%) brought by males. This change in food delivery rates did not result in a delay in laying, but there was a significant difference in mean clutch size between years (2.71 ± 0.49 eggs in 2004 and 2.05 ± 0.78 eggs in 2005) without any within-year variation in relation to the laying dates. The egg size (volume and length) was related to the year (2004 < 2005), suggesting a trade-off in the quantity and the quality of eggs between the two seasons. We also found no evidence that the investment in a large clutch affected nestling BCI in the course of the food shortage season. Since many pairs (about 60%) interrupted breeding during the incubation stage, we assumed that parents that succeeded in rearing nestlings in these conditions were probably ‘high-quality’ individuals. Our results therefore showed that whiskered terns are sensitive to the varying food conditions they experienced throughout the courtship period. The diversity of prey types could be a key factor in the reproductive investment of this tern species.     

Effects of a food supplementation experiment on reproductive investment and a post-mating sexually selected trait in magpies Pica pica

Food availability is an important factor affecting breeding success in birds. Food supplementation experiments in birds have in general focused on the effects on reproductive success in terms of female investment (laying date, clutch size, egg size), however, it is also known that the estimation of mate quality based on sexually selected signals influences female reproductive investment. In the particular case of magpies, females use nest size, a post-mating sexually selected signal, to assess male's likelihood to invest in reproduction, and accordingly adjust reproductive investment (clutch size). Then, the possible effects of food supplementation on female reproductive investment could be mediated by other variables related to parental quality, such as nest size in magpies. In the present study, we explore if higher food availability in a magpie territory affected both male sexually selected traits (i.e. nest size) and female reproductive investment (laying date, egg size, clutch size). We performed a food supplementation experiment in which we experimentally increased food availability in several magpie territories, keeping others as controls. In food-supplemented territories, males built significantly larger nests and females significantly increased egg size by 4.1% compared to control females. Results suggest that the continuous provisioning of protein rich food allowed magpie females to increase egg size. However, laying date and clutch size did not differ between control and food-supplemented magpie pairs. Food availability also affected the relationship between female reproductive investment and nest size. In control territories, females decreased their egg size in response to a larger nest, whereas a tendency for the opposite relationship was revealed in food-supplemented territories. We discuss the possibility that magpie females adopt different strategies for reproductive investment according to food availability.     

A phylogenetic analysis of egg size,clutch size,spawning mode,adult body size,and latitude in reef fishes

Theoretical treatments of egg size in fishes suggest that constraints on reproductive output should create trade-offs between the size and number of eggs produced per spawn. For marine reef fishes, the observation of distinct reproductive care strategies (demersal guarding, egg scattering, and pelagic spawning) has additionally prompted speculation that these strategies reflect alternative fitness optima with selection on egg size differing by reproductive mode and perhaps latitude. Here, we aggregate data from 278 reef fish species and test whether clutch size, reproductive care, adult body size, and latitudinal bands (i.e., tropical, subtropical, and temperate) predict egg size, using a statistically unified framework that accounts for phylogenetic correlations among traits. We find no inverse relationship between species egg size and clutch size, but rather that egg size differs by reproductive mode (mean volume for demersal eggs = 1.22 mm³, scattered eggs = 0.18 mm³, pelagic eggs = 0.52 mm³) and that clutch size is strongly correlated with adult body size. Larger eggs were found in temperate species compared with tropical species in both demersal guarders and pelagic spawners, but this difference was not strong when accounting for phylogenetic correlations, suggesting that differences in species composition underlies regional differences in egg size. In summary, demersal guarders are generally small fishes with small clutch sizes that produce large eggs. Pelagic spawners and egg scatterers are variable in adult and clutch size. Although pelagic spawned eggs are variable in size, those of scatterers are consistently small.     

山地麻蜥的雌性繁殖和孵出幼体特征

山地麻蜥年产多窝卵。窝卵数、窝卵重和卵重与雌体体长呈正相关,卵重与窝卵数无关。窝卵数、窝卵重和卵重不存在明显的季节变化。卵长径与卵短径呈正相关,卵长径、卵短径与窝卵数无关。雌体通过增加窝卵数和卵大小增加繁殖输出。孵出幼体的体重、体长、尾长、躯干干重、刺余卵黄不存在季节差异,但5月份孵出幼体的脂肪体高于4月份。     

The trade‐off between clutch size and egg mass in tree swallows Tachycineta bicolor is modulated by female body mass

Egg production is a costly component of reproduction for female birds in terms of energy expenditure and maternal investment. Because resources are typically limited, clutch size and egg mass are expected to be constrained, and this putative trade‐off between offspring number and size is at the core of life history theory. Nevertheless, empirical evidence for this trade‐off is equivocal at best, as individual heterogeneity in resource acquisition and allocation may hamper the detection of the negative correlation between egg number and mass within populations. Here, we investigated how female body mass and landscape composition influences clutch size, egg mass, and the relationship between these two traits. To do so, we fitted linear mixed models using data from tree swallows Tachycineta bicolor breeding in a network of 400 nestboxes located along a gradient of agricultural intensity between 2004 and 2011. Our dataset comprised 1463 broods for clutch size analyses and 4371 eggs (from 847 broods laid between 2005–2008) for egg mass analyses. Our results showed that agricultural intensity negatively impacted clutch size, but not egg mass nor the relationship between these two traits. Female mass, on the other hand, modulated the trade‐off between clutch size and egg mass. For heavier females, both traits increased jointly, without evidence of a trade‐off. However, for lighter females, there was a clear negative relationship between clutch size and egg mass. This work shows that accounting for individual heterogeneity in body mass allows the detection of a clutch size/egg mass trade‐off that would have remained undetected otherwise. Identifying habitat and individual effects on resource allocation towards reproductive traits may help bridging the gap between predictions from theory and empirical evidence on life history trade‐offs.     

State-dependent incubation behaviour in the high arctic barnacle geese

Energetic trade-offs between time spent on incubation and times spent on foraging for nesting birds give individuals in good body condition the possibility to incubate more continuously. In the present paper, the incubation behaviour of female barnacle geese Branta leucopsis was quantified in a colony in Svalbard. Females were weighted in early incubation and feeding recess lengths and frequencies were recorded. The feeding behaviour during the course of incubation was significantly correlated to by body mass, and heavy females had both fewer and shorter feeding recesses than lighter females. Moreover, there was an increase in the number of feeding recesses and the total feeding time as the incubation period progressed. Neither clutch size nor egg laying date had an effect on incubation behaviour. However, clutch size was positively related to female body mass suggesting that high-quality females produce large clutches but also allocate more body reserves to incubation. Females left the nest to feed at all times of the day, but more frequently during day time. This was not related to their body mass. Females presumably leave their nest at the time of day when the costs to reheat eggs are at a minimum. The diurnal rhythm may also be adjusted to the activity by egg predators. Overall the results support the state-dependent hypothesis for incubation behaviour, suggesting that body condition at the start of incubation is an important factor for incubation behaviour in barnacle geese.     

How avian incubation behaviour influences egg surface temperatures: relationships with egg position,development and clutch size

While understanding heat exchange between incubating adults and their eggs is central to the study of avian incubation energetics, current theory based on thermal measurements from dummy eggs reveals little about the mechanisms of this heat exchange or behavioural implications for the incubating bird. For example, we know little about how birds distribute their eggs based on temperature differences among egg positions within the nest cup. We studied the great tit Parus major, a species with a large clutch size, to investigate surface cooling rates of individual eggs within the nest cup across a range of ambient temperatures in a field situation. Using state‐of‐the‐art portable infrared imaging and digital photography we tested for associations between egg surface temperature (and rate of cooling) and a combination of egg specific (mass, shape, laying order, position within clutch) and incubation specific (clutch size, ambient temperature, day of incubation) variables. Egg surface temperature and cooling rates were related to the position of the eggs within the nest cup, with outer eggs being initially colder and cooling quicker than central eggs. Between foraging bouts, females moved outer eggs significantly more than centrally positioned eggs. Our results demonstrate that females are capable of responding to individual egg temperature by moving eggs around the nest cup, and that the energy cost to the female may increase as incubation proceeds. In addition, our results showing that smaller clutches experience lower initial incubation temperatures and cool quicker than larger clutches warrant further attention for optimal clutch size theory and studies of energetic constraints during incubation. Finally, researchers using dummy eggs to record egg temperature have ignored important elements of contact‐incubation, namely the complexity of how eggs cool and how females respond to these changes.     

Nutritional quality of prebreeding diet influences breeding performance of the Florida scrub-jay

Food supplementation studies of breeding birds have traditionally concentrated on energetic constraints on breeding performance. It is only recently that the nutritional quality of the prebreeding diet has also been considered influential. We examined the importance of specific nutrients in the prebreeding diet of the Florida scrub-jay ( Aphelocoma coerulescens). Birds were provided with one of two supplements (rich in protein and fat or rich in fat only) prior to breeding in 2000 and 2001 and their breeding performance, in relation to unsupplemented (control) birds, was examined. Birds receiving both supplements significantly advanced laying in both years, and increased clutch size in 2000 but not in 2001. Laying date explained variation in clutch size in birds on dietary supplements. Egg mass and volume declined with laying order, irrespective of dietary treatment, but birds on the high fat, high protein diet laid heavier third eggs than controls and this was independent of laying date. Laboratory analysis of 14 abandoned and unhatched eggs revealed that as egg mass increased so did the absolute amount of protein and water while fat content remained relatively fixed. Using these relationships between the masses of egg components and fresh egg mass, we calculated that heavier third eggs laid by birds on high fat and high protein, compared with those laid by controls, contained more water that may be fundamental to chick growth and survival. This is the first demonstration for an avian species that nutritional quality of prebreeding diet can simultaneously influence laying date, clutch size, and egg size and composition.     

Maturation increases early reproductive investment in Adélie Penguins Pygoscelis adeliae

Correlations between female investment in egg production and age, breeding experience and laying date have been reported in several seabird species. In general, clutch and egg sizes increase with female age and breeding experience but decrease with laying date. Positive correlations of clutch and egg size with age and breeding experience can be caused by an increase in reproductive investment with maturation or they may be an artefact of lower survival rates for individuals with poor-quality phenotypes. Negative correlations of clutch and egg size with laying date might signal an adaptive reduction in egg production or be due in part to variation among individuals. We examined the interactions of female age, breeding experience, laying date and clutch and egg size in Adélie Penguins Pygoscelis adeliae . Breeding experience strongly affected clutch size with 87.3% of all one-egg clutches laid by first-time breeders. In addition, increasing age had a positive influence on egg size and was associated with earlier laying dates. However, there was little evidence to suggest that either clutch or egg sizes are influenced by laying date. Laying dates and clutch and egg sizes did not affect a female's probability of returning to breed in the following year, indicating that increased investment is a product of maturation and not of the loss of poor-quality breeders from the population. Our results suggest that as female Adélie Penguins gain foraging and breeding experience they are able to initiate breeding earlier, to lay complete clutches of two eggs and to lay larger eggs.     

安徽滁州雌性丽斑麻蜥繁殖特征

在安徽滁州地区丽斑麻蜥(Eremias argus)年产两窝卵。窝卵数及窝卵重与雌体体长呈正相关,相对窝卵重与雌体体长无关,卵重与窝卵数无关。窝卵数、窝卵重及卵重在窝序间无明显的差异。卵长径与卵短径呈正相关,卵长径与窝卵数呈负相关,而卵短径与窝卵数无关。雌体主要通过增加窝卵数增加繁殖输出。     

Patterns of life history among cyclopoid copepods of central Europe

• 1 Life history characters (body size of adults, egg diameter, egg sac length and breadth) of nineteen species of central European cyclopoid copepods were measured and sexual size dimorphism (adult female length x adult male length^?1), relative egg size (egg weight X body weight^?1), weight of adult females and of eggs, egg sac shape (egg sac length x egg sac breadth^?1), and reproductive effort (clutch weight produced per female weight per day) were calculated to detect trends in life history strategies.
• 2 Typical planktonic species exhibited the lowest reproductive effort. Among planktonic species, the value for egg sac shape increased with clutch size.
• 3 Large species and small species exhibited different trends in life history characters. Large species had larger clutches, larger eggs, and a greater sex size dimorphism than small species. However, small species had a greater relative egg size.
• 4 Large species live in cold water and reproduce during the spring bloom of phytoplankton where the production of large clutches with relatively small eggs is advantageous. Reserves are unnecessary for juveniles because food is abundant. Small species generally are most abundant during the warm season, when conditions are less predictable, and relatively large eggs, possibly provided with reserves, are advantageous.

     

Geographical variation in egg size of the Great Tit Parus major: a new perspective

A recent study on geographical variation in egg size of Great Tits Parus major concluded that: (1) mean egg size tended to increase with increasing latitude; and (2) mean egg size was positively correlated with mean clutch size. Including new data on both egg and clutch size, we reanalysed the relationships between egg size, clutch size and latitude, and investigated the possible effects of habitat type, female body size and egg shape on these relationships. We found that (1) egg volume showed minimum values around 51°N, increasing both north and southwards; (2) female body size increased linearly with increasing latitude; (3) female body size was positively correlated with egg breadth, but not with egg length or egg volume; (4) the sphericity index of the eggs (breadth to length ratio) was largest at medium latitudes, and eggs were more elongated towards the north and the south; (5) the relationship between clutch size and latitude was curvilinear, with the largest clutch sizes at intermediate latitudes; (6) egg size was not correlated with clutch size when the complete latitudinal range was considered, but egg size was negatively correlated with clutch size between 40 and 51°N; and (7) egg size did not differ among habitat types. We suggest that female body size (which probably limits egg breadth), and the pressure for producing large eggs (which in turn increases the reproductive success) are the main determinants of geographical variation in egg size and shape. Populations of small-bodied Great Tits seem to escape from the limits of their size, producing relatively elongated eggs, so that from a certain latitude southwards, egg volume does not decrease in spite of a decrease in female body size. Moreover, the negative relationship between egg and clutch size at low latitudes suggests that energetic trade-offs may also contribute to determine egg size in the south.     

Egg mass in an asynchronously hatching parrot: does variation offset constraints imposed by laying order?

Life history theory predicts phenotypic trade-offs between the number and quality of offspring produced. Intraspecific variation in egg mass is common in birds and increased egg size can have positive effects on offspring fitness. However, evidence of a trade-off with clutch size is limited. We analyzed variation in mass of 5,743 Green-rumped parrotlet (Forpus passerinus) eggs laid over 15 years to evaluate the potential for facultative adjustment of egg mass and factors governing variation. Heavier eggs had an increased probability of both hatching and fledging but egg mass did not affect postfledging recruitment. Offspring egg mass differed between populations and the potential for seasonal adjustment to egg mass may be related to environmental factors such as seed density. Egg mass was moderately heritable (h ²=0.42) which accounts for some of the individual variation detected, and these results are likely attributable to strong maternal effects. We found an effect of female age on egg mass, but no effects of previous reproductive experience. Finally, egg mass was strongly governed by position within the laying sequence, independent of clutch size, and such adjustment may facilitate brood reduction under some conditions in this highly asynchronous species.     

New Insights into Non-Avian Dinosaur Reproduction and Their Evolutionary and Ecological Implications: Linking Fossil Evidence to Allometries of Extant Close Relatives

It has been hypothesized that a high reproductive output contributes to the unique gigantism in large dinosaur taxa. In order to infer more information on dinosaur reproduction, we established allometries between body mass and different reproductive traits (egg mass, clutch mass, annual clutch mass) for extant phylogenetic brackets (birds, crocodiles and tortoises) of extinct non-avian dinosaurs. Allometries were applied to nine non-avian dinosaur taxa (theropods, hadrosaurs, and sauropodomorphs) for which fossil estimates on relevant traits are currently available. We found that the reproductive traits of most dinosaurs conformed to similar-sized or scaled-up extant reptiles or birds. The reproductive traits of theropods, which are considered more bird-like, were indeed consistent with birds, while the traits of sauropodomorphs conformed better to reptiles. Reproductive traits of hadrosaurs corresponded to both reptiles and birds. Excluding Massospondylus carinatus , all dinosaurs studied had an intermediary egg to body mass relationship to reptiles and birds. In contrast, dinosaur clutch masses fitted with either the masses predicted from allometries of birds (theropods) or to the masses of reptiles (all other taxa). Theropods studied had probably one clutch per year. For sauropodomorphs and hadrosaurs, more than one clutch per year was predicted. Contrary to current hypotheses, large dinosaurs did not have exceptionally high annual egg numbers (AEN). Independent of the extant model, the estimated dinosaur AEN did not exceed 850 eggs (75,000 kg sauropod) for any of the taxa studied. This estimated maximum is probably an overestimation due to unrealistic assumptions. According to most AEN estimations, the dinosaurs studied laid less than 200 eggs per year. Only some AEN estimates obtained for medium to large sized sauropods were higher (200-400 eggs). Our results provide new (testable) hypotheses, especially for reproductive traits that are insufficiently documented or lacking from the fossil record. This contributes to the understanding of their evolution.     

Hatching asynchrony that maintains egg viability also reduces brood reduction in a subtropical bird

In birds, hatching failure is pervasive and incurs an energetic and reproductive cost to breeding individuals. The egg viability hypothesis posits that exposure to warm temperatures prior to incubation decreases viability of early laid eggs and predicts that females in warm environments minimize hatching failure by beginning incubation earlier in the laying period, laying smaller clutches, or both. However, beginning incubation prior to clutch completion may incur a cost by increasing hatching asynchrony and possibly brood reduction. We examined whether Florida scrub jays (Aphelocoma coerulescens) began incubation earlier relative to clutch completion when laying larger clutches or when ambient temperatures increased, and whether variation in incubation onset influenced subsequent patterns of hatching asynchrony and brood reduction. We compared these patterns between a suburban and wildland site because site-specific differences in hatching failure match a priori predictions of the egg viability hypothesis. Females at both sites began incubation earlier relative to clutch completion when laying larger clutches and as ambient temperatures increased. Incubation onset was correlated with patterns of hatching asynchrony at both sites; however, brood reduction increased only in the suburbs, where nestling food is limiting, and only during the late nestling period. Hatching asynchrony may be an unintended consequence of beginning incubation early to minimize hatching failure of early laid eggs. Food limitation in the suburbs appears to result in increased brood reduction in large clutches that hatch asynchronously. Therefore, site-specific rates of brood reduction may be a consequence of asynchronous hatching patterns that result from parental effort to minimize hatching failure in first-laid eggs. This illustrates how anthropogenic change, such as urbanization, can lead to loss of fitness when animals use behavioral strategies intended to maximize fitness in natural landscapes.