Variation In Reproductive Performance Research Articles

Diet Composition Explains Interannual Fluctuations in Reproductive Performance in a Lowland Golden Eagle Population

Food supply stands out as one of the most critical drivers of population demographics by limiting reproductive rates. In this study, we assessed fluctuations in diet composition and monitored various reproductive parameters over a nine-year period in a Golden Eagle population in an Eastern European peatland. The identification of 2439 prey specimens from 84 species revealed that the studied eagles primarily preyed upon birds (constituting 78.3% of prey numbers and 67.2% of prey biomass) and less on mammals (21.6% and 32.8%, respectively). Grouse emerged as the most important prey group (31% and 27%), followed by waterfowl (17%) and hares (8% and 14%). The most significant prey species, both in terms of numbers and weight, were the Black Grouse, Mountain Hare, Common Crane, and Capercaillie. The share of the Black Grouse decreased, while those of the White-fronted Goose, Roe Deer, and hares increased. The food niche, as measured by the Levins’ index, was broad (6.6), and it expanded during the study. On average, 58.3% of Golden Eagle pairs initiated breeding annually, with 69.1% successfully completing it, and 0.41 young per occupied territory were produced annually; there was pronounced interannual variation in reproductive performance. These fluctuations were associated with the shares of White-fronted Goose, Capercaillie, Mountain Hare and Roe Deer in the diet, suggesting that these species may be gaining increasing importance for the Golden Eagle, particularly following the decline of the Black Grouse.

Latitudinal variation in reproductive performance of hermit crabs (Anomura: Paguroidea) in two marine provinces along the Brazilian coast

ABSTRACT We performed a comparative analysis of fecundity and reproductive effort of two hermit crab species, Clibanarius antillensis and Calcinus tibicen, distributed along the two marine provinces in Brazilian coast. Samples of both species were manually collected during spring low tides on a two-month basis, from February 2011 to January 2012 at locations separated by ~ 3000 km: North-eastern (NE) region – Pedra Rachada Beach (Ceará); South-eastern (SE) region – Araçá Beach and Grande Beach (São Paulo). The size of ovigerous females, as well as the fecundity values, egg volume, internal volume of occupied shells, and reproductive effort were analysed, and the results evidenced significantly higher values for females of both species collected in SE localities. In females collected NE, there was also the presence of aberrant eggs, which influenced the reproductive parameters analysed for these species, resulting in lower reproductive effort. Biomass invested in egg production varied between populations, but ovigerous females of SE invested a higher percentage of their weight in the production of its egg mass, showing significant differences in the reproductive effort. Variation in reproductive performance detected for both species may be related to latitudinal location and associated to the habitat’s characteristics.

O-033 Factors associated with variation in reproductive performance of ewes inseminated laparoscopically

O-033 Factors associated with variation in reproductive performance of ewes inseminated laparoscopically

Agricultural management, bedrock, and vulnerability of sexual reproduction to climate change affect the occurrence of a European near-endemic moss

We investigated whether the European near-endemic moss Drepanocladus lycopodioides has declined in its core distribution area in the southern Baltic Sea region and explored potential explanations for this. First, we re-visited sites with documented records from 1854 to 1957 in the Stockholm archipelago and nearby mainland in southern Sweden. Second, we compared the numbers and distributions of Swedish occurrences, their habitats, and substrates up to 1950 (289 herbarium records), and from 1951 onwards (347) using different map layers. Third, we explored whether inter-annual variation in reproductive performance was related to moisture conditions at five sites on an island in the Stockholm archipelago during nine years. We estimated moisture conditions based on precipitation data and dry days during the time when fertilization occurs in the year prior to sporophyte maturation. Drepanocladus lycopodioides has strongly decreased in intensively managed agricultural landscapes but remains frequent in natural or semi-natural habitats on limestone. Sporophyte development varied between years and depended on the weather condition during the fertilization period. Climate forecasts for the study area predict longer dry spells during late spring to late summer, which coincides with the timing of sexual branch initiation and fertilization in the species. We expect that sporophyte production will likely decrease in the future, which will affect the species’ abilities to re-colonize spots where it vanishes during years with poor growth conditions.

Nest‐boxes alter the reproductive ecology of urban cavity‐nesters in a species‐dependent way

Human‐provided nesting shelters such as nest‐boxes mitigate the shortage of natural breeding sites. Since artificial nests are not where animals evolved and optimised their reproductive performance, it remains inconclusive if these are adequate substitutes, ensuring equivalent fitness returns while breeding. In particular, most knowledge on the ecology of cavity‐nesting birds comes from nest‐box populations, but no study has directly compared fitness consequences of breeding inside nest‐boxes in relation to natural cavities in cities. We directly compare the reproductive performance, life‐history trait variation and fitness consequences for two small passerines, blue and great tits, breeding in nest‐boxes as opposed to natural cavities in an urban deciduous forest. We use a quasi‐experimental setting to comprehend the conservation potential of these artificial cavities and to support/question generalisations stemming from nest‐box studies. We show that the effects of cavity type vary between species: in blue tits, fitness proxies were negatively affected by nest‐boxes (lower fledging success and fledgling numbers, longer time spent in the nest and later fledging date relative to natural cavities), while in great tits, the fitness proxies were unaffected by cavity type. Importantly, we detected accelerated incubation in both species breeding in nest‐boxes. No differences in pre‐hatching traits (lay date, clutch size, hatching rates) between cavity types suggest that the fitness deterioration occurred because of post‐hatching effects. We highlight the ecological importance of old‐growth tree stands, providing natural cavities for city‐breeding animals and the need for quantifying alterations of reproductive ecology in other taxa using human‐provided nests. Owing to the detected cavity type‐dependent variation in reproductive performance, we support the criticism regarding the unconditional extrapolation of evolutionary and ecological interpretations of nest‐box studies to general populations.

Microclimate influences plant reproductive performance via an antagonistic interaction

Climatic conditions can influence plant reproduction directly, but also via changes in plant traits, interactions with animals, and the surrounding environment. Such indirect effects can often be complex and involve multiple steps including climatic effects on interacting species, and on the context in which these interactions occur. The joint effects of climatic variation and indirect effects in terms of plant-animal interactions have sometimes been assessed at larger spatial scales. However, less is known about how microclimatic variation affects within-population variation in reproductive performance, in spite of that it is becoming increasingly clear that variation in climatic conditions can occur over very short distances. We studied the direct and indirect effects of microclimate on within-population variation in reproductive performance of the plant Gentiana pneumonanthe in presence of the myrmecophagous and seed predator butterfly Phengaris alcon. We found that microclimatic effects on plant performance were mainly indirect, and that effects of temperature and moisture were interactive. The number of seeds per flower of G. pneumonanthe decreased in cold and moist microsites, and these effects were mediated by an increased oviposition by P. alcon in these microsites. The effects of soil temperature and moisture on the incidence of oviposition and plant performance were mediated by effects on plant phenology, density and phenology of neighbouring host plants, and host ant abundance. Plants that flowered earlier and where host ants were more abundant, and especially plants surrounded by fewer and later-flowering neighbours, produced fewer seeds per flower because of a higher incidence of oviposition. Our results demonstrate that effects of microclimatic variation on plant reproductive performance can be mostly indirect and largely mediated by species interactions. These findings highlight that among individual variation in small-scale environmental conditions within populations can cause variation in individual plant performance through multiple pathways.

Age-specific reproduction in female pied flycatchers: evidence for asynchronous aging

Age-related variation in reproductive performance is central for the understanding of population dynamics and evolutionary processes. Our understanding of age trajectories in vital rates has long been limited by the lack of distinction between patterns occurring within- and among-individuals, and by the lack of comparative studies of age trajectories among traits. Thus, it is poorly understood how sets of demographic traits change within individuals according to their age. Based on 40 years of monitoring, we investigated age-related variation in five reproductive traits in female pied flycatchers (Ficedula hypoleuca) including laying date, clutch size, brood size, nest success (probability that a nest produces at least one chick) and egg success of successful nests (proportion of eggs resulting in a chick). We disentangled within- from among-individual processes and assessed the relative contribution of within-individual age-specific changes and selective appearance and disappearance. Finally, we compared the aging pattern among these five reproductive traits. We found strong evidence for age-specific performance including both early-life improvement and late-life decline in all reproductive traits but the egg success. Furthermore, the aging patterns varied substantially among reproductive traits both for the age of peak performance and for the rates of early-life improvement and late-life decline. The results show that age trajectories observed at the population level (cross-sectional analysis) may substantially differ from those occurring at the individual level and illustrate the complexity of variation in aging patterns across traits.

Crown defoliation decreases reproduction and wood growth in a marginal European beech population.

Abiotic and biotic stresses related to climate change have been associated with increased crown defoliation, decreased growth and a higher risk of mortality in many forest tree species, but the impact of stresses on tree reproduction and forest regeneration remains understudied. At the dry, warm margin of species distributions, flowering, pollination and seed maturation are expected to be affected by drought, late frost and other stresses, eventually resulting in reproduction failure. Moreover, inter-individual variation in reproductive performance versus other performance traits (growth, survival) could have important consequences for population dynamics. This study investigated the relationships among individual crown defoliation, growth and reproduction in a drought-prone population of European beech, Fagus sylvatica. We used a spatially explicit mating model and marker-based parentage analyses to estimate effective female and male fecundities of 432 reproductive trees, which were also monitored for basal area increment and crown defoliation over 9 years. Female and male fecundities varied markedly between individuals, more than did growth. Both female fecundity and growth decreased with increasing crown defoliation and competition, and increased with size. Moreover, the negative effect of defoliation on female fecundity was size-dependent, with a slower decline in female fecundity with increasing defoliation for the large individuals. Finally, a trade-off between growth and female fecundity was observed in response to defoliation: some large trees maintained significant female fecundity at the expense of reduced growth in response to defoliation, while some other defoliated trees maintained high growth at the expense of reduced female fecundity. Our results suggest that, while decreasing their growth, some large defoliated trees still contribute to reproduction through seed production and pollination. This non-coordinated decline of growth and fecundity at individual level in response to stress may compromise the evolution of stress-resistance traits at population level, and increase forest tree vulnerability.

Age-related reproductive performance of the Adélie penguin, a long-lived seabird exhibiting similar outcomes regardless of individual life-history strategy.

Age-related variation in reproductive performance in long-lived iteroparous vertebrate species is common, with performance being influenced by within-individual processes, such as improvement and senescence, in combination with among-individual processes, such as selective appearance and disappearance. Few studies of age-related reproductive performance have compared the role of these drivers within a metapopulation, subject to varying degrees of resource competition. We accounted for within- and among-individual changes among known-aged Adélie penguins Pygoscelis adeliae during 17years (1997-2013), at three clustered colonies of disparate size, to understand patterns in age-related reproductive success during early and late adulthood. Age at first reproduction (AFR) was lowest, and number of breeding attempts highest, at the largest colony. Regardless of AFR, success improved with early post-recruitment experience. For both oldest and youngest recruitment groups, peak performance occurred at the end of their reproductive life span indicating a possible cost of reproduction. Intermediate recruitment groups reached peak performance in their mid-reproductive life span and with intermediate breeding experience, before decreasing. Breeding success was lowest for the initial breeding attempt regardless of AFR, but we observed subsequent variation relative to recruitment age. Gaining experience by delaying recruitment positively influenced reproductive performance early in the reproductive life span and was most evident for the youngest breeders. Oldest recruits had the highest initial and peak breeding success. Differences in AFR resulted in trade-offs in reproductive life span or timing of senescence but not in the overall number of breeding attempts. Patterns differed as a function of colony size, and thus competition for resources. Early life improvement in performance at the larger colonies was primarily due to within-individual factors and at the largest colony, AFR. Regardless of colony size late-life performance was positively related to the age at last reproduction, indicating selective disappearance of lower performing individuals. These results highlight that different life-history strategies were equally successful, indicating that individuals can overcome potential trade-offs associated with early- and late-life performance. These results have important implications for understanding the evolution of life-history strategies responsible for driving population change.

CAUSES OF VARIATION IN REPRODUCTIVE PERFORMANCE OF WEST AFRICAN DWARF GOAT

Analysis was carried out on the reproductive performance of 59 WAD (Foula djullon) goats over 8 year period 1982-1990) under intensive management. The data involving a total of 176 kiddings comprising 311 kids were analysed to provide some information on the reproductive potential and the distribution of the Sexes on the WAD goats for an appraisal of its utilization for future genetic and environmental studies and the improvement of the breed in Nigeria. The results showed no significant seasonal effect on the kidding pattern. Singles, twins and triplets were 33.44, 48,23 and 16,40% respectively. Kidding interval varied from 91 to 2.10 days, annual kidding rate was 1..68 with mean kid birth weight of 1.5 +0.138, 1.49 +0.65 and 1.31+0.095kg for single twins and multiple births respectively. The average sex ratio was 48.79+0.18. The least squares constants showed that the age of dam, kidding interval and Season of kidding have significant effect on the sex ratio with more males born by those after 3 years of age particularly during the dry season 't shorter kidding intervals or 191-220 days. Calculated frequency of sex combination of males to females was 0.4005, 0.4662 and 0.1333 trizygotic, dizygotic and monozygotic twins among the triplets - The frequency was 0.67 for monzygotic twinning among the twin births. Although preweaning mortalities of 12.26, 16.33 and 19.36% were recorded for single, twin and multiple births respectively, highly significant survival rate was recorded in the dry season (84.40+0.75) than in the wet season 81,18 +0.75 whilst the kidding interval was between 200 - 240 days in about 56% of the population studied. The current emphasis on the presence of monozygotic twins with a frequency of 67% among twin birth and 13.3% among the triplets is to assist in utilizing this trait in the goat for studies that could enhance the modification of the environment or improve the genetic potentials of the breed.

High fertility cycle

Over the past 2 decades, a reproduction revolution has occurred in the dairy industry in which average 21-d pregnancy rates have more than doubled from around 14% to more than 30% in many herds. Much of this increase in reproductive performance has been driven by development and adoption of fertility programs. Despite the dramatic increase in 21-d pregnancy rates, substantial variation exists among herds using the exact same reproductive management, suggesting that factors other than fertility programs can affect fertility. Change in body weight or body condition score postpartum or during the periparturient period dramatically affects embryo quality, reproductive outcomes, and transition cow health. Although some cows lose body weight or body condition score after calving, some cows maintain, whereas some cows even gain body weight or body condition score during this time period. Surprisingly, milk production during early lactation is not affected based on body condition score change during the first 3 weeks postpartum; however, peak milk measured near 60 DIM was less in both primiparous and multiparous cows that either gained or maintained compared to cows that lost body condition during the 1st 30 DIM. The high fertility cycle coupled with the dramatic increases in reproductive performance due to the development and adoption of fertility programs is a new paradigm that we can now use to explain much of the variation in reproductive performance among herds. The high-fertility cycle: how timely pregnancies in 1 lactation may lead to less BCS loss, fewer health issues, greater fertility, and reduced early pregnancy losses in the next lactation.

Seasonal variation of giant gourami (Osphronemus goramy) spawning activity and egg production in aquaculture ponds

The giant gourami Osphronemus goramy Lacépède, 1801, spontaneously spawns in captivity, making nests for egg deposition when suitable nest supports and nesting material are made available in rearing facilities. The seasonal variation in reproductive performance of the giant gourami was characterized during a 20-month experiment in two compartmentalized ponds (about 550 m2 each) at a fry production center in West Java, Indonesia. A total of 208 giant gourami broodfish were introduced in the two experimental ponds, with a sex-ratio of one male to three females in each of the 52 spawning compartments delimited by vertical nets. Nesting supports in each spawning compartment were examined every two days for the presence of eggs resulting from natural reproduction. Three performance indicators were quantified from the collected nests: spawning frequency (monthly number of spawns per female), effective fecundity (number of eggs per spawn) and egg quality (estimated from the proportion of clear living eggs in each spawn). The seasonality of giant gourami reproduction was analyzed as a function of seasonal variation in rainfall, rearing water temperature and day length. Based on a total of 413 collected spawns, the multiple linear regression models did not show any significant relationship between giant gourami spawning frequency and the three environmental variables studied. In contrast, the number of eggs per spawn was highly and positively related to rainfall (p < .0001), moderately and negatively related to water temperature (p < .001), and weaklier and negatively related to day length (p < .01). The proportion of clear eggs was positively related to day length (p < .01). Overall, this study represents one of the first comprehensive datasets on the reproductive phenology of giant gourami, and as such will be helpful in formulating broodfish management strategies for the species.

Reproductive performance of northern Australia beef herds. 2. Descriptive analysis of monitored reproductive performance

A population-based epidemiological study was conducted between 2007 and 2011 and involved 78 northern Australian commercial beef-breeding herds and in excess of 56 000 cattle concurrently monitored. Cow reproductive performance was described from the biannual assessment of fetal age and lactation status. Both novel and well established measures of performance were used within four broad country types and included the following: percentage of lactating cows pregnant within 4 months of calving; percentage of cows pregnant within an approximate 12-month reproductive cycle (annual pregnancy); fetal and calf loss between confirmed pregnancy and weaning; percentage of cows contributing a calf at weaning and percentage of non-pregnant females retained for re-mating. The results from the present study described the variation in reproductive performance of commercial beef herds across northern Australia and defined typical and achievable levels of performance. The results from the study suggest that a weaning rate of 66% is a more realistic target level of performance for the Northern Forest, while weaning rates of at least 75–80% are realistic for other country types. Female-cattle performance was much lower in the Northern Forest than in the other country types. In absolute terms, there were 15–20% fewer surviving mated cows contributing a calf at weaning in an annual production year and ~4% more missing pregnant cows, which was associated with the ~20% higher retention of non-pregnant cows for re-mating. The reproductive performance of herds varied substantially among and within country types, with a 20–30% variation in reproduction rates and 5–15% variation in fetal and calf loss for half of the herds in all regions. Further analyses were performed and identified the major causes of this variation and are reported in subsequent papers within this series. The results from the present study appear to suggest that substantial opportunities to increase the reproductive performance of northern beef herds exist, providing that the causes of this variation are able to be identified and alleviated.

Differences in the breeding performance of great tits Parus major between a forest and an urban area: a long term study on first clutches

The great tit Parus major inhabits various types of forests, yet it prefers deciduous forests. In the urbanized areas it is one of the commonest bird species, even where only isolated trees are present, which seems to be a relatively recent phenomenon. This paper presents results of a long-term study (2002–2015) of variation in reproductive performance (number of hatchlings, hatching success, number of fledglings, fledging success, breeding success and nest failure rate) in first clutches of two great tit populations nesting in two contrasting habitats: a mature deciduous forest and an urban parkland, in central Poland. This study shows a clear and sustained spatial pattern of variation where the forest population of great tits produced more hatchlings and fledglings per successful nests than the urban park site population. Breeding success and fledging success demonstrate a similar but slightly less obvious pattern, with higher values for the forest site than the urban parkland area occurring consistently in the vast majority of years. Also hatching success was generally slightly higher in the forest than in the urban park but did not show such a clear spatial pattern. Only the nest failure rate was higher in the forest than in the urban parkland. We suggest that caterpillar richness in the forest compared to the urban parkland is one of the key drivers of the observed differences in the breeding performance between the study habitats. We also found positive correlations between fledgling numbers and caterpillar abundance and between fledgling numbers and mean May temperatures in the forest, whereas neither breeding nor fledging success showed such correlations. In the urban parkland, fledgling numbers as well as fledging and breeding successes were positively correlated with mean May temperatures. The between-population variation we found probably reflects a more general difference between urban and forest populations of tits.

Seasonal Variations in Reproductive Performance of Crossbred Cows in Kerala and the Influence of Climatic Stress Factors over a Period of Six Years

Seasonal Variations in Reproductive Performance of Crossbred Cows in Kerala and the Influence of Climatic Stress Factors over a Period of Six Years

Evidence of age-related improvement in the foraging efficiency of Ad\xe9lie penguins

Age variation in reproductive performance is well-documented but the mechanisms underlying this variation remain unclear. Foraging efficiency is likely to be a key source of demographic variation as it determines the amount of energy that can be invested in fitness-related activities. Evidence of age-related changes in the foraging efficiency of adult seabirds is scarce and inconsistent. We investigated the effects of age on the foraging efficiency of breeding Adélie penguins, a relatively short-lived seabird species, in order to gain a broader perspective on the processes driving variation in ageing rates. We found support for a positive effect of age, either linear or levelling off at old ages, on both our proxies for daily catch rate and catch per unit effort. Across all age classes, males were more performant foragers than females. We found no strong evidence for differing ageing patterns between sexes or individual quality levels, and no evidence for senescence. We infer that continuous individual improvement could be responsible for a larger amount of the variation in foraging efficiency with age at our study site, compared with selective disappearance of underperforming phenotypes. The different results reported by other studies highlight the need to conduct longitudinal studies across a range of species in different environments.

Selecting for changes in average "parity curve" pattern of litter size in Large White pigs.

This study aimed to analyse genetic background of variation in reproductive performance between parities of a sow and to investigate selection strategies to change the "parity curve". Total number born (TNB) recorded in Large White sows was provided by Topigs Norsvin. Analysis with basic (BM) and random regression (RRM) models was done in ASReml 4.1. The BM included only a fixed "parity curve", while RRM included 3rd order polynomials for additive genetic and permanent sow effects. Parameters from RRM were used in simulations in SelAction 2.1. Based on Akaike information criterion, RRM was a better model for TNB data. Genetic variance and heritability estimates of TNB from BM and RRM were increasing with parity from parity 2. Genetically, parity 1 is the most different from parities 7 to 10, whereas most similar to parities 2 and 3. This indicates presence of genetic variation to change the "parity curve". Based on simulations, the selection to increase litter size in parity 1 only increases TNB in all parities, but does not change the observed shape of "parity curve", whereas selection for increased TNB in parity 1 and reduced TNB in parity 5 decreases differences between parities, but also reduces overall TNB in all parities. Changing the "parity curve" will be difficult as the genetic and phenotypic relationships between the parities are hard to overcome even when selecting for one parity.

Latitudinal variation in reproductive performance of Leymus chinensis: implications for its response to future climate warming

ABSTRACTBackground: Sexual reproduction of plants is likely to be related to climate in their distribution range. Therefore, the investigation of spatial pattern of reproductive traits might provide valuable insights into the potential responses of a plant species to climate change.Aims: We studied the latitudinal pattern of sexual reproduction in Leymus chinensis to uncover the underlying ecological factors and their roles.Methods: We established a latitude transect in the Inner Mongolian steppe and investigated reproductive performance of L. chinensis, followed by modelling the relationship between traits and ecological factors.Results: Stalk height, spike length and spikelet number were non-linearly related to latitude. The spike-stalk ratio, seed viability and shoot density displayed significantly negative response to increasing latitude. Overall, increased latitude posed adverse impacts on sexual reproduction of L. chinensis. Annual mean temperature was positively correlated with the traits relevant to fitness, such as floret number and seed viability and annual mean precipitation to the development and growth of shoots.Conclusions: Under climate change scenarios, the shift of reproductive pattern in L. chinensis, i.e. likely more successful sexual reproduction, will have considerable contribution to its potential of adaptation to changing environment, and to its capacity of migration towards more suitable habitats.

Ventral colour, not tail streamer length, is associated with seasonal reproductive performance in a Chinese population of Barn Swallows (Hirundo rustica gutturalis)

Phenotypic differentiation is common among populations that have large geographic distributions. One proposed mechanism driving phenotype divergence is sexual selection, which predicts that trait differences among closely related populations are underlain by variation in reproductive performance. Here, we examined a population of Asian Barn Swallows (Hirundo rustica gutturalis) in northeastern China. We ask whether traits shown to be under divergent sexual selection in other Barn Swallow populations are under sexual selection in this north Asian population by determining whether two features of phenotype variation, tail streamer length and ventral plumage colouration (including both throat and belly regions), are sexually dimorphic, associated with patterns of assortative mating and predictive of reproductive success. In this population, the length of tail streamers did not correlate with ventral plumage colouration in either males or females. The length of tail streamers was sexually dimorphic, but we did not find assortative mating by tail streamer length. By contrast, we found no sexual dichromatism but we did find assortative mating by throat colouration. Our correlational results indicated that the breeding performance of male Barn Swallows was associated with differences in their ventral plumage colouration, suggesting that ventral plumage colouration is likely a target of sexual selection in this population. Our finding that tail streamer length is unlikely to be under sexual selection is consistent with studies of other H. rustica gutturalis populations. The result that ventral plumage colour is likely to be under sexual selection is partially consistent with previous studies on Japanese H. rustica gutturalis, in which male throat but not belly plumage colour is the sexually selected trait.

Reproductive Contributions of Cardinals Are Consistent with a Hypothesis of Relaxed Selection in Urban Landscapes

Human activities are leading to rapid environmental change globally and may affect the eco-evolutionary dynamics of species inhabiting human-dominated landscapes. Theory suggests that increases in environmental heterogeneity should promote variation in reproductive performance among individuals. At the same time, we know that novel environments, such as our urbanizing study system, may represent more benign or predictable environments due to resource subsidies and ecological changes. We tested the hypothesis that reduced environmental heterogeneity and enhanced resource availability in cities relax selective pressures on birds by testing if urban females vary less than rural females in their demographic contributions to local populations. From 2004-2014, we monitored local population densities and annual reproductive output of 470 female Northern Cardinals (Cardinalis cardinalis) breeding at 14 forested sites distributed across a rural-to-urban landscape gradient in Ohio, USA. Reproductive contribution was measured as the difference between individual and site-averaged annual reproductive output across all nesting attempts, divided by the annual density at each site. We show that among-individual variation in reproductive contribution to the next year’s population declined with increasing urbanization, despite similar variability in body condition across the rural-urban gradient. Thus, female cardinals that bred in urban habitats within our study area were more similar in their contribution to the next generation than rural breeders, where a pattern of winners and losers was more evident. Within-individual variation in annual reproductive contribution also declined with increasing urbanization, indicating that performance of females was also more consistent among years in urban than rural landscapes. These findings are consistent with the hypothesis that urbanized environments offer more homogeneous or predictable conditions that may buffer individuals from environmental heterogeneity and relax natural selection.