Date Of First Egg Research Articles

Temperature Dependence of the Breeding Parametres of the Collared Flycatcher (Passeriformes, Muscicapidae) in the National Park Homilshanski Lisy (NE Ukraine)

The breeding phenology of Collared Flycatchers was studied over an 11-year period (2006‒2011 and 2013‒2017) in oak-maple-lime stands located in the Northern-East of Ukraine (in the National Park Homilshanski Lisy). In most years, egg laying began in the first and second ten-day periods of May. The earliest recorded first-egg date (368 broods) was 23 April, while the latest was 5 May. These dates varied from year to year. The relationship between the first-egg date and the date of daily average temperature transition through + 10 °C suggests that birds bred earlier due to warmer local temperatures. The clutch size was negatively correlated with the date of the average air temperature transition through + 5 °C. The earliest hatching date was 15 May, and the latest was 25 May. Fledging typically began in the first half of June. The breeding season’s length ranged from 30 to 42 days, and the breeding cycle was positively correlated with the transition of the average daily temperature through +5 °C. To determine which factors explained the first egg date and clutch size, Generalized Linear Models (GLMs) were conducted. GLMs suggest a correlation between the first-egg date and the sum of effective temperatures (∑T150), arrival date temperature, migration route temperature, and average temperature of the third decade of April. Clutch size is determined by the sum of effective temperature accumulation (∑130) and migration route temperature. Reproductive success is negatively correlated with the average of 30 daily temperatures until the median date.

The phenology and clutch size of UK Blue Tits does not differ with woodland composition

The deciduous tree‐herbivorous caterpillar‐insectivorous bird food chain is a well‐studied system for investigating the impacts of climate change across trophic levels. To date, across Europe, most attention has focused on the impacts of increasing spring temperature on changes to phenology in Oak‐dominated (Quercus spp.) woodlands. Paridae species and Pied Flycatcher Ficedula hypoleuca are the most studied secondary consumers, all of which demonstrate an advancement in reproductive phenology with increases in spring temperature. Shifts in climate and phenology may also impact on reproductive investment in clutch size, and the effects of climate on phenology and clutch size may vary depending on woodland composition. To date, the effects of among‐habitat variation in phenology and reproductive investment have received little attention. Insectivorous birds inhabiting woodlands that differ in tree composition may differ in the timing of breeding, due to local tree leafing phenology acting as a cue for egg‐laying date and/or clutch size. Moreover, for most insectivorous birds, woodland composition within a territory is likely to be the main determinant of food availability for both adults and chicks. Consequently, if warming springs affect the temporal patterns of food availability differently across different woodland compositions, this may affect the optimal average local phenology for nesting birds. Here, using data from 34 long‐term (mean 15 years) nest monitoring sites across the UK, we investigate the effect of woodland tree composition and temperature on Blue Tit Cyanistes caeruleus first egg date (FED) and clutch size. We supplemented the nest monitoring data by quantifying woodland composition, at a site level, through modified point counts. We predict that birds breeding in woodlands with greater proportions of late‐leafing species, such as Oak and Ash Fraxinus excelsior, will breed later than those breeding in woodlands with greater proportions of early‐leafing species, such as Birch Betula spp. and Beech Fagus sylvatica. We found no evidence for differences in Blue Tit FED or clutch size in relation to the proportion of any of the tree species investigated, after controlling for temperature and latitude (FED: −3.4 and 2.2, clutch size: −0.4 and − 0.2 eggs for one‐unit increase in temperature and latitude, respectively). In recent decades and across all sites, clutch size has decreased as spring temperatures have increased, a strategy which could allow birds flexibly to adjust their breeding phenology such that nestling demand coincides with peak food availability. The lack of an effect of woodland composition on Blue Tit phenology suggests Blue Tits do not fine‐tune their reproductive phenology to the local tree composition. Whether this lack of evidence for phenological divergence is due to an absence of divergent selection on breeding phenology and clutch size or to gene flow is not clear.

The Effect of Floods on Nest Survival Probability of Common Sandpiper Actitis hypoleucos Breeding in the Riverbed of a Large Lowland European River

The natural valleys of large rivers provide suitable nesting and foraging sites for many bird species. In this study, we assess the effects of water fluctuations during the breeding season on Common Sandpipers’ nest survival on a semi-natural section of the Vistula River, and evaluate which tactics this species can adopt to minimise the effects on a long-term scale. Birds can avoid losses due to flooding by adjusting the timing of nesting to avoid the occurrence of extreme water conditions, and/or by choosing a safe nesting location. We found that nest location is a direct response to periodic high water, and the threat of flooding seems to be one of the important determinants of Common Sandpiper nest placement. The choice of nest location is not random, as 70% of pairs nested above a height that provides an 80% chance of avoiding flooding of the nest. For the lowest-lying nests found in this study, nesting success was reduced up to 92% because of inundation. Birds choose more elevated places, even during the second half of the season when the threat of flooding is lower. Their preference for nesting above a certain height does not change over the breeding season, which corresponds to the very small impact of the date of first egg laying on breeding success. Those who breed earlier in the season have a slightly higher risk of being flooded, but nesting in more elevated places reduces this risk much more than shifting the time of breeding.

Low Repeatability of Breeding Events Reflects Flexibility in Reproductive Timing in the Pied Flycatcher Ficedula hypoleuca in Spain

Individual flexibility in breeding time is essential to respond to unpredictable changes in environmental conditions. Repeatability quantifies the consistency of the expression of phenotypes over time due to differences between individuals. Here, we estimate the repeatability of breeding date (laying date of first egg), hatching date and timing of pre-breeding events in a population of Pied Flycatchers Ficedula hypoleuca monitored over three decades in central Spain. We found low repeatabilities of breeding and hatching dates (respectively, R = 0.135 and R = 0) and among-year fluctuations (R = 0.276 and R = 0.218) in the expression of these traits. Repeatabilities of mating dates and of the interval between mating and egg laying were also very low (respectively R = 0.053 and R = 0) and among years (respectively R = 0.218 and R = 0.172), suggesting that Pied Flycatcher females are flexible to adjust their breeding schedule to current breeding conditions. We interpret the low consistency of traits related to breeding phenology as strong support for female phenotypic plasticity in breeding timing and the potential of such traits to respond to changing environmental conditions.—Le Vaillant, J., Potti, J., Camacho, C., Canal, D. & Martínez-Padilla, J. (2022). Low repeatability of breeding events reflects flexibility in reproductive timing in the Pied Flycatcher Ficedula hypoleuca in Spain. Ardeola, 69: 21-39.

Double brooding of Tree Swallows (Tachycineta bicolor) in southeast Tennessee

Double brooding, a second breeding attempt following the successful fledging of a previous brood, has the potential to substantially increase annual reproductive success of a given bird species. Tree Swallows (Tachycineta bicolor) have a wide breeding distribution, which makes them suitable subjects for looking at effects of environmental variation on their breeding biology. One aspect of Tree Swallow breeding that is not well studied is double brooding. During this study, double brooding was frequent, ranging from 37% to 57% each year. Single broods and first broods did not differ from each other, however second broods had smaller clutches, fewer fledglings, and reduced hatching success. Double brooded females had a median date of first egg laying that was 5 d earlier than single brooded females. Based on other studies of double brooding in Tree Swallows, the observed differences may be attributable to factors such as reduced food supplies later in the season, female age, breeding experience, and/or nesting date. The results demonstrate the necessity for studying this species over a broader portion of its range to better understand its population dynamics and reproductive potential.

Great and blue tit laying dates vary with fine-scale variation in local tree composition but not tree budburst

Many studies have investigated how spring temperature affects laying dates and how this in turn affects the synchrony between nestling food demands and the insect food peak that follows tree budburst. While there is strong evidence that temperature itself acts as a cue for this plasticity in annual timing, the exact nature of the cue and response remains to be elucidated. Here we use long-term data on Great and Blue Tits and an unprecedented dataset on the location and phenology of 1396 trees to investigate whether small-scale variation in laying date can be explained by local tree phenology, and/or by tree species composition around nestboxes. Individual trees maintained their relative timing of budburst between years, while differences among tree species were more variable between springs. Contrary to expectation, we found no relation between first-egg dates and average budburst date at different distances around the nestbox. This can at least partly be explained by the very low degree of spatial autocorrelation in tree budburst. We did find an effect of local tree composition whereby Blue Tits, but not Great Tits, laid earlier in nestboxes surrounded by more oaks and fewer beeches. Although Blue Tit nest failure rate was higher in territories with more beech trees, independently of laying date, we found no evidence for preferential occupation of oak-dominated territories. Thus although we found some evidence for fine-scale effects of tree species on timing of breeding, the underlying mechanism remains unclear.

European Starling Nest‐site Selection Given Enhanced Direct Nest Predation Risk

ABSTRACTThe European starling (Sturnus vulgaris) is recognized, outside its native range, as an invasive species, and efforts to deter its nesting have generally been unsuccessful. Enhancing perceived risk at the nest site is a little‐explored route in developing a nest deterrent. Specifically, nest predation risk affects site selection, reproduction, antipredator behavior, and fitness in nesting birds. We questioned whether perceived predation risk as related to a snake model positioned inside a nest box, in striking form, moving, and present throughout the period of cavity site selection would induce European starlings to avoid or delay nest construction. We conducted our study on the 2,200‐ha National Aeronautics and Space Administration Plum Brook Station (PBS), Erie County, Ohio, USA. Our objectives were to examine nest initiation, clutch development, and hatching success by starlings relative to 4 nest‐box treatments: moving snake model, movement mechanism only, immobile snake model, and control (empty box). We applied treatments across 120 nest boxes on PBS (30 boxes/treatment) from 15 April through 17 June 2019. We observed no treatment effects on nest initiation or date of nest bowl formation. Starlings occupied (laid ≥1 egg) in 76% of nest boxes (moving snake model = 22 boxes, movement mechanism = 25 boxes, immobile snake model = 21 boxes, control = 23 boxes). We observed no effects of treatment on likelihood of starlings laying a clutch, date of first egg, clutch size, or hatching success. We suggest that starlings adapted to perceived risk because models, despite animacy, did not attack. Therefore, snake models, as developed herein, are ineffective starling nesting deterrents. Published 2021. This article is a U.S. Government work and is in the public domain in the USA.

Predator scent and visual cue applied to nest boxes fail to dissuade European Starlings (Sturnus vulgaris) from nesting

Indirect predator cues have been shown to enhance perceived nest predation risk in both open-cup and cavity-nesting birds. We hypothesized that scent from the raccoon (Procyon lotor) inside nest boxes, supplemented with raccoon hair as a visual cue on the outside of the box, would enhance perceived risk to the European Starling (Sturnus vulgaris), resulting in reduced use of treated nest boxes and negative effects on reproduction. The starling is recognized, outside its native range, as a competitor with indigenous cavity nesters and a pest species, and efforts to deter its nesting have generally been unsuccessful. Our objectives were to examine nest initiation, clutch development, and hatching success by starlings relative to 4 nest box treatments. Starlings selected from nest boxes treated with a novel visual cue at the entry hole, predator scent inside the nest box and supplemented with a predator visual cue at the entry hole, the predator visual cue, or a novel odor inside the box and supplemented with the novel visual cue at the entry hole (n = 120 boxes; n = 30 per treatment). Starlings established nest bowls in 65% of nest boxes (novel visual cue = 21 boxes, predator scent/predator visual cue = 19 boxes, predator visual cue = 17 boxes, novel odor/novel visual cue = 21 boxes); clutches (≥1 egg) were laid in 80 boxes, but 2 boxes contained a single egg with no nest. We observed no effects of treatment on likelihood of starlings laying a clutch, date of first egg, clutch size, or hatchling number. We conclude that raccoon scent inside nest boxes, supplemented by raccoon hair as a visual cue, failed to enhance perceived risk to starlings such that nesting was deterred. We suggest that direct or indirect experience with nest predation attempts (which enhance perceived risk) and the starling's plasticity in antipredator responses are key hurdles in development of an efficacious nesting deterrent. Therefore, we encourage the evaluation of direct predation risk via use of predator effigies on or in nest boxes, as well as in foraging areas proximate to nest boxes.

Examining carry‐over effects of winter habitat on breeding phenology and reproductive success in prairie warblers Setophaga discolor

Winter habitat quality can influence breeding phenology and reproductive success of migratory birds. Using stable isotope ratios of carbon (δ13C) from bird claws and red blood cells collected in Massachusetts, USA, we assessed if winter habitat occupancy carried over to affect prairie warbler Setophaga discolor breeding arrival dates, body condition upon arrival, pairing success, first‐egg dates and reproductive success. In two of three years (in 2011 and 2012, but not in 2013), after‐second‐year (ASY) males wintering in drier habitat, as indicated by enriched δ13C values, arrived later on the breeding grounds. Based on the North Atlantic Oscillation index, there was likely less rainfall in the Caribbean wintering grounds during the winters of 2011 and 2012 compared to the winter of 2013, suggesting increased winter rainfall in 2013 may have diminished the influence of winter habitat occupancy on arrival date. We did not find any effects of winter habitat on breeding season phenomena for second‐year (SY) males or females, but our sample sizes for these age/sex classes were relatively low. Although winter habitat quality influenced arrival dates of ASY males, there was no evidence that it affected reproductive performance, perhaps because of high rates of nest depredation in our system. Our study adds to a growing body of research that shows the influence of carry‐over effects can differ among species and within populations, and also can be modulated by other environmental conditions. This information enriches our understanding of the role of carry‐over effects in population limitation for migratory birds.

European Starling (Sturnus vulgaris) reproduction undeterred by predator scent inside nest boxes

Indirect predator cues near nests have been shown to enhance perceived predation risk and associated antipredator behaviours in breeding animals across taxa and particularly with birds. We hypothesized that scent from the raccoon (Procyon lotor (Linnaeus, 1758)) inside nest boxes would, despite being an evolutionarily unique predator, enhance perceived risk to the European Starling (Sturnus vulgaris (Linnaeus, 1758)), thus reducing use of treated sites and reproduction. During early spring, starlings selected from nest boxes treated with equal volumes of predator scent, a novel odour, or water (n = 40 boxes per treatment). We evaluated effects of treatment on reproductive traits via generalized linear models. Starlings established nest bowls in 61% of nest boxes (predator scent, n = 27 boxes; novel odour, n = 24 boxes; control (water), n = 22 boxes); clutches were laid in 68 boxes. We observed no effects of treatment on the likelihood of a clutch (≥1 egg) or nest failure. Further, we found no treatment effects on date of first egg, clutch size, or hatchling number. We conclude that starling antipredator response to enhanced, indirect risk of nest predation is contingent upon a combination of predator cues, as well as direct or indirect experience with nest predation.

Experimental manipulation of photoperiod and temperature does not influence nest size in Blue and Great tits

ABSTRACT To anticipate future breeding conditions in spatiotemporally dynamic environments, any proximate aspect of breeding is expected to be causally associated with environmental cues or constraints. Photoperiod, ambient temperature, and food are considered to be among the most important environmental determinants of breeding performance. However, the importance of these determinants in the expression of nest size has not previously been investigated experimentally in laboratory conditions. We report that captive Blue Tits (Cyanistes caeruleus) and Great Tits (Parus major) did not adjust the size of their cavity nest to experimental changes in photoperiod or ambient-temperature regimes. Results did not change when we controlled for first-egg date and clutch size. In addition, captive birds fed ad libitum did not build larger nests than free-ranging breeders in standardized nest boxes. Thus, we report no evidence that nest size per se is proximately influenced by commonly studied environmental factors l...

Nest design in a changing world: great tit Parus major nests from a Mediterranean city environment as a case study.

Investigations of urbanization effects on birds have focused mainly on breeding traits expressed after the nest-building stage (e.g. first-egg date, clutch size, breeding success, and offspring characteristics). Urban studies largely ignored how and why the aspects of nest building might be associated with the degree of urbanization. As urban environments are expected to present novel environmental changes relative to rural environments, it is important to evaluate how nest-building behavior is impacted by vegetation modifications associated with urbanization. To examine nest design in a Mediterranean city environment, we allowed urban great tits (Parus major) to breed in nest boxes in areas that differed in local vegetation cover. We found that different measures of nest size or mass were not associated with vegetation cover. In particular, nests located adjacent to streets with lower vegetation cover were not smaller or lighter than nests in parks with higher vegetation cover. Nests adjacent to streets contained more pine needles than nests in parks. In addition, in nests adjacent to streets, nests from boxes attached to pine trees contained more pine needles than nests from boxes attached to other trees. We suggest that urban-related alterations in vegetation cover do not directly impose physical limits on nest size in species that are opportunistic in the selection of nesting material. However, nest composition as reflected in the use of pine needles was clearly affected by habitat type and the planted tree species present, which implies that rapid habitat change impacts nest composition. We do not exclude that urbanization might impact other aspects of nest building behaviour not covered in our study (e.g. costs of searching for nest material), and that the strengths of the associations between urbanization and nest structures might differ among study populations or species.

Nest size is positively correlated with fledging success in Corsican Blue Tits (Cyanistes caeruleus) in an insular oak-dominated habitat mosaic

Avian nests function to provide a safe environment for parents, eggs and nestlings. Positive associations between nest size and other components of breeding performance are expected in two conditions. First, larger nests protect nest occupants better against environmental fluctuations (e.g., weather) than smaller nests. This implies that nest size is a determinant of survival in nest occupants. Second, if reproduction is physically costly, “stronger” parents are expected to be able to build both larger nests and rear more offspring. Here we present the findings of a 17-year correlative nest box study in Corsican Blue Tits (Cyanistes caeruleus ogliastrae) that examined the associations between nest size and different aspects of breeding success. We found that females with larger nests produced more fledglings, but did not produce more hatchlings or heavier nestlings than females with smaller nests. The analyses involving nest size controlled for other female characteristics (first-egg date, clutch size, female age) and environmental factors (oak habitat type, weather during the nestling stage) which we assumed could influence aspects of breeding success. Our findings concerning associations between the size of the nest and breeding success differ from those reported in previous studies in other geographic regions, perhaps because the costs that are associated with reproduction or the local environmental conditions that influence breeding performance are population specific. Our correlative study illustrates that avian studies of niche construction may benefit from long-term multi-factor investigations.

Coal TitsPeriparus aterBuild Larger Nests Than Blue TitsCyanistes caeruleusand Great TitsParus majorLiving in the Same Mediterranean Coniferous Woodland Habitat

Abstract. The size and shape of the nest are species-specific characteristics that are often associated with environmental factors at the time of breeding. Nests are expected to be larger or thicker in colder environments, although the relationships between nest design and weather differ between species. Here we present the results of an analysis of the external height of the nest wall in Paridae that accepted small standardized nesting boxes for breeding. The study populations were monitored in a relatively cold Mediterranean study area. We found that Coal Tits Periparus ater built higher external nest walls than Great Tits Parus major or Blue Tits Cyanistes caeruleus, after controlling for the first-egg date and clutch size which are assumed to reflect aspects of the quality of the nest builders. Our measures of nest size were not closely associated with the average ambient temperature, but nest walls tended to be shallower when there was more rain. Nest-shape asymmetry, as reflected in the difference i...

Nest size is not closely related to breeding success in Blue Tits: A long-term nest-box study in a Mediterranean oak habitat

ABSTRACT Various components of breeding success are predicted to be related to avian nest size because (1) some individuals are physically able to build larger nests than other individuals or (2) larger nests provide more protection in the absence of predation than smaller nests. The results of an 18-yr correlative nest-box study in Blue Tits (Cyanistes caeruleus) show that nest size is not closely related to components that reflect breeding performance, after controlling for other female characteristics (first-egg date, clutch size, and female age) assumed to influence breeding performance in long-term studies. Our results support those of most short-term field studies that have reported weak associations between nest size and breeding performance in cavity-nesting passerines. We suggest that the absence of an association between nest size and breeding performance can be explained by the fact that the vast majority of nest-box studies have used small nest chambers that imposed physical constraints on the...

A proxy of social mate choice in prairie warblers is correlated with consistent, rapid, low-pitched singing

In songbirds, female mate choice may be influ- enced by how well a male performs his songs. Performing songs well may be especially difficult if it requires maximiz- ingmultipleaspectsofperformancesimultaneously.Wethere- fore hypothesized that, in a population of prairie warblers, the males most attractive to females would be those with superior performance in more than one facet of singing. We tested this prediction by comparing different aspects of song perfor- mance, as well as different combinations of these aspects, to determine which were the best predictors of first-egg date, which we took to be a proxy for social mate choice. We found thatfirst-egg datewasbestpredicted bya combination ofsong performance traits that included consistent performance, rapid rate, and low pitch. Female preference for males capable of physically challenging song performance may have contribut- ed to the evolution of acoustically complex vocalizations in oscine songbirds, because if complex sounds are more difficult to perform, they may be favored by selection for signal reliability.

Plumage ornaments in male Northern Lapwings Vanellus vanellus may not be a reliable indicator of their mating success

Conspicuous morphological traits that signal aspects of physical state of the owner may be used as cues in mate choice, leading to sexual selection of ornamental traits. In birds, colour patterns as well as structural attributes may constitute ornaments affecting mate choice. In the breeding season, Northern Lapwing Vanellus vanellus males possess long crests, contrast-rich black and white facial markings, a black breast, and a shining greenish dorsal side. In non-breeding and juvenile plumages, and in females, crests are shorter, facial patterns have less clear contrasts, and breast and dorsal side possess varying amounts of light fringes. Depending onmoult energetics in latewinter/early spring, when males acquire their breeding plumage, the state of these characters could potentially signal male condition to females prospecting for mates. We examined if these traits correlated with male mating success in this polygynous species, predicting males with the most expressed ornamental characters (a) tomate earlier and (b) to gain more mates.Trait states were ranked for 31 males of which breeding phenology and number of mates were known. No correlationwas found between trait expression and date of first egg laid on the territory and number of mates did not correlate with trait expression. Thus, the study did not confirm that females use crest length, breast blackness and face contrasts or lack of dorsal fringes as cues in their mate choice. This could be because the elaborate traits do not have an ornamental function important for femalemate choice, but experimental studies would be needed to rigorously test this hypothesis.

Nest site characteristics and breeding success of the red-backed shrike (Lanius collurio) in agricultural landscape in eastern Poland: Advantage of nesting close to buildings

One of the most important factors influencing breeding success in many bird species is predation. Nest site choice is one way of lowering the probability of such losses. In an agricultural landscape of eastern Poland, we examined the relationship between red-backed shrike (Lanius collurio) nest site characteristics, i.e., height above ground, concealment, and occurrence of thorns, and the risk of nest predation. We also considered the relationship with distance to potential predators, i.e., corvid nests, and the distance to buildings. Our results showed that only 1 environmental factor significantly influenced breeding success. Birds nesting closer to buildings achieved higher breeding success than those more distant from buildings. A positive correlation between date of first egg laying and distance from the nest to the buildings was also found. These results indicate that areas with human activities and buildings can created habitats that improve breeding success for some species. On the other hand, the growth of such habitats also contributes to decreasing availability of semi-natural areas for breeding and foraging for these species.

The breeding biology of Rose-ringed Parakeets Psittacula krameri in England during a period of rapid population expansion

Capsule The reproductive rate of Rose-ringed Parakeets in the UK was higher in 2001-2003 than previously estimated.Aim To measure reproductive rate and the factors affecting this in Rose-ringed Parakeets in England during a period of rapid expansion in population of this potential invasive species.Methods During 2001–2003, 108 nests were located and monitored in southwest London, southeast London and the Isle of Thanet. Nest survival using the Mayfield method, fledging success and the characteristics of the nest and surrounding vegetation were measured.Results The mean date of first egg was 26 March ± 1.3 days and the median clutch size was 4 eggs. Mayfield nest survival rate was 72%. Reproductive success was 1.4 ± 0.3 young fledged per nest. Parakeets bred predominantly in ash (Fraxinus) and oak (Quercus). Nest trees had a diameter at breast height (DBH) of 73.7 ± 4.7 cm (mean ± se).Conclusion Reproductive success in this parakeet was higher than previously estimated (0.8 young fledged per nest prior to 1999). This reproductive output is sufficient to explain the rapid increase in Rose-ringed Parakeet numbers (from an estimated 1500 birds in 1996 to nearly 10,000 birds by 2004) if Rose-ringed Parakeets have a low death rate similar to other parrots.

Decomposing the seasonal fitness decline

Seasonal fitness declines are common, but the relative contribution of different reproductive components to the seasonal change in the production of reproductive young, and the component-specific drivers of this change is generally poorly known. We used long-term data (17 years) on breeding time (i.e. date of first egg laid) in northern wheatears (Oenanthe oenanthe) to investigate seasonal reproductive patterns and estimate the relative contributions of reproductive components to the overall decline in reproduction, while accounting for factors potentially linked to seasonal declines, i.e. individual and habitat quality. All reproductive components-nest success (reflecting nest predation rate), clutch size, fledging success and recruitment success-showed a clear decline with breeding time whereas subsequent adult survival did not. A non-linear increase in nest predation rate caused nest success to decline rapidly early in the season and level off at ~80% success late in the breeding season. The combined seasonal decline in all reproductive components caused the mean production of recruits per nest to drop from around 0.7-0.2; with the relative contribution greatest for recruitment success which accounted for ~50% of the decline. Our data suggest that changing environmental conditions together with effects of nest predation have strong effects on the seasonal decline in fitness. Our demonstration of the combined effects of all reproductive components and their relative contribution shows that omitting data from later stages of breeding (recruitment) can greatly underestimate seasonal fitness declines.