Seasonal Reproductive Success Research Articles

Fitness costs of an immune response in the house martin (Delichon urbica)

Immune responses constitute a major way for hosts to defend themselves against parasites. Because hosts do not habitually produce strong responses all the time, immune responses might be costly to produce or maintain. We tested experimentally if the production of a response to a challenge with a novel antigen resulted in a cost in terms of fitness using the highly colonial house martin Delichon urbica as a model system. We injected adult breeding birds during laying of the first clutch with either Newcastle disease virus (NDV) or a control injection, and the clutch was subsequently removed to induce relaying. NDV stimulates the non-specific immune system, causing production of antibodies during a period of more than 2 weeks. Accordingly, we found an increase in leukocyte counts in experimental birds compared to controls. Experimental treatment reduced the frequency of re-laying, caused a delay in timing of relaying and a reduction in brood size. Quality of nestlings in terms of body size, body mass and T-cell-mediated immune response did not differ significantly between treatments. Overall, seasonal reproductive success differed significantly between treatments, showing that the production of an immune response by adult birds is costly in terms of future fecundity.

FRAGMENTION BY AGRICULTURE INFLUENCES REPRODUCTIVE SUCCESS OF BIRDS IN A SHRUBSTEPPE LANDSCAPE

Shrubsteppe communities are among the most imperiled ecosystems in North America as a result of conversion to agriculture and other anthropogenic changes. In the Intermountain West of the United States, these communities support a unique avifauna, including several species that are declining and numerous others that are of conservation concern. Extensive research in the eastern and central United States and in Scandinavia suggests that fragmentation of formerly continuous forests and grasslands adversely affects reproductive success of birds, yet little is known of the potential effects on avian communities in Western shrublands. I used multi-model inference to evaluate the potential effects of local and landscape variables on nest predation and brood parasitism, and behavioral observations of color-banded birds to evaluate the potential effects of habitat fragmentation on seasonal reproductive success of passerines in the shrubsteppe of eastern Washington State, USA. Reproductive success of shrubsteppe-obligate passerines was lower in landscapes fragmented by agriculture than in continuous shrubsteppe landscapes. Daily survival rates for nests of Brewer's Sparrows (Spizella breweri; n=496) and Sage Thrashers (Oreoscoptes montanus; n=128) were lower in fragmented landscapes, and seasonal reproductive success (percentage of pairs fledging young) of Sage Sparrows (Amphispiza belli; n=146) and Brewer's Sparrows (n=59) was lower in fragmented landscapes. Rates of parasitism by Brown-headed Cowbirds (Molothrus ater) overall were low (4%) but were significantly greater in fragmented landscapes for Brewer's Sparrows, and parasitism resulted in fewer young fledged from successful nests. Simple models of population growth using landscape-specific fecundity and estimates of adult survival derived from return rates of banded male Sage Sparrows and Brewer's Sparrows suggest that fragmented shrubsteppe in Washington may be acting as a population sink for some species. Immediate conservation needs include halting further fragmentation of shrubsteppe, restoring low-productivity agricultural lands and annual grasslands to shrubsteppe where possible, and convincing the public of the intrinsic value of these imperiled ecosystems.

Settlement patterns of female barn swallows Hirundo rustica across different group sizes: access to colorful males or favored nests?

In most avian species, individuals are faced with two critical decisions at the start of a breeding season: choosing a breeding site and a mate. An analysis of these decisions in light of population-level patterns, such as group size variation in social breeders, can illuminate the causes and patterns of habitat selection behavior. Group sizes are variable in barn swallows; however, no clear and consistent benefits of group breeding have been found in this species, and it is puzzling as to why individuals breed socially. Previous analyses demonstrated that individuals aggregate to gain access to nests that were constructed during previous seasons; however extra-pair matings are also prevalent in this species, raising questions about the mate-selection strategies of females across different group sizes. In this paper, I address the question of how females make their first site-selection decisions in terms of two features known to be causally related to seasonal reproductive success: (1) colorful males or (2) old nests. Using experimental and observational data, I tested, but found no support for, the hypotheses that propose female settlement decisions are a function of (1) the prevalence of colorful males or (2) the increased opportunity for extra-pair matings at group sites. Instead, it is apparent that female settlement patterns are strongly tied to the availability of old nests at a site. Extra-pair fertilizations are equally common across all group sizes in this population, suggesting that females do not face a trade-off between old nests and the possibility of extra-pair mating decisions when making settlement decisions.

Male tail streamer length does not predict apparent or genetic reproductive success in North American barn swallowsHirundo rustica erythrogaster

In the socially monogamous barn swallow, previous studies of individuals in the European subspeciesHirundo r. rusticahave shown that a male's tail streamer length is under strong sexual selection and is positively associated with several measures of reproductive success, including a low probability of being cuckolded by other males. The prominence of these results has led to subsequent experimental and correlational investigations of individuals in the phenotypically divergent subspeciesH. r. erythrogasterin North America, where it has been shown that male tail streamer length is not as strongly associated with reproductive success as in European populations. We examined relationships between male tail streamer length and patterns of: (1) social mate selection and reproductive success, and (2) extra‐pair paternity in 265 progeny of 53 social fathers within a New York barn swallow population. Although tail streamers in this population were sexually dimorphic, male tail streamer length did not predict patterns of mate selection, seasonal reproductive success, or extra‐pair paternity. Moreover, in contrast to the strong positive relationships between paternity and male streamer length in European populations, summarized in this paper, we found no positive relationship between a male's paternity of young in the nest he is attending and his tail streamer length in our study population in New York. Our results further corroborate recent suggestions that the function of sexual signals varies geographically in this species, although we await additional experimental analyses on streamer lengths to understand the maintenance of sexual dimorphism in this trait.

BROOD SEX RATIOS ARE RELATED TO MALE SIZE BUT NOT TO ATTRACTIVENESS IN COMMON YELLOWTHROATS (GEOTHLYPIS TRICHAS)

Abstract When the reproductive value of sons differs from that of daughters, selection will favor broods biased toward the sex that can provide greater fitness benefits. In species where female choice is based on male ornamentation, females mated to highly ornamented males may experience a reproductive advantage by skewing the brood sex ratio toward sons. In the Common Yellowthroat (Geothlypis trichas), males with larger black facial masks are more likely to gain a social mate and sire extrapair young and, as a result, have increased seasonal reproductive success. Females mated to larger-masked males could benefit if they produced more sons. Given that larger- masked males are preferred as extrapair sires, females may also benefit by producing more extrapair sons. We tested these hypotheses during a five-year study of Common Yellowthroats in Wisconsin. Contrary to our predictions, females did not produce more sons when mated to males with larger masks, and extrapair young were not more likely to be male. ...

Brood Sex Ratios are Related to Male Size but not to Attractiveness in Common Yellowthroats (Geothlypis Trichas)

AbstractWhen the reproductive value of sons differs from that of daughters, selection will favor broods biased toward the sex that can provide greater fitness benefits. In species where female choice is based on male ornamentation, females mated to highly ornamented males may experience a reproductive advantage by skewing the brood sex ratio toward sons. In the Common Yellowthroat (Geothlypis trichas), males with larger black facial masks are more likely to gain a social mate and sire extrapair young and, as a result, have increased seasonal reproductive success. Females mated to larger-masked males could benefit if they produced more sons. Given that larger- masked males are preferred as extrapair sires, females may also benefit by producing more extrapair sons. We tested these hypotheses during a five-year study of Common Yellowthroats in Wisconsin. Contrary to our predictions, females did not produce more sons when mated to males with larger masks, and extrapair young were not more likely to be male. However, sons were more likely to be sired by males with longer tarsi, which suggests that females may respond to male body size rather than to male ornament size.El Cociente de Sexos en las Nidadas Está Relacionado con el Tamaño de los Machos pero no con el Atractivo en Geothlypis trichas

Nest-site selection in the barn swallow, Hirundo rustica: What predicts seasonal reproductive success?

Despite hundreds of studies, we know very little about the causes and fitness-related consequences of nest-site selection. For example, it is not typically known whether the rarely reported fitness consequences of site selection are the result of nest, individual, or nest-site variables or combinations of these factors. Reuse of previously constructed nest sites is a prevalent behavior in many animals and offers the opportunity to experimentally tease apart whether seasonal reproductive success is a function of nest, individual, or nest-site characteristics. I used observational and experimental data to test three hypotheses related to these factors in association with barn swallow ( Hirundo rustica L., 1758) nest reuse. While both nest and individual characteristics explain variation in seasonal reproductive success, nest location per se is not an important factor defining the outcome of nest-site selection. Whereas traits related to habitat and individual characteristics are likely confounded in correlational studies, my experiments demonstrate a causal relationship between seasonal reproductive success and aspects of the nest and individual, the latter explaining more variation in the model than nest characteristics. Knowledge of the relative roles of individual, nest, and nest-site attributes are important for understanding the causes and consequences of habitat selection behavior.

Sex-specific consequences of life in the city

The vast majority of species are excluded from human-dominated landscapes, but some species persist and appear to thrive, despite facing challenges they would not encounter in less disturbed habitat. Corticosteroid (cort) secretion may play a significant role in enabling an animal to cope with urban breeding habitat because it helps mediate physiological and behavioral responses to environmental challenges. Here we present tests of 3 hypotheses relating to cort secretion in urban animals: 1) environmental challenges vary between urban and rural habitat, as reflected in differing levels of cort secretion in animals breeding in these habitat types, 2) there are fitness correlates associated with variation in cort levels within populations, and 3) parasite load is one of the mechanistic links between variation in cort levels and reproductive success. Male white-crowned sparrows (Zonotrichia leucophrys) in urban habitat had significantly higher baseline corticosterone levels than males in rural habitat, whereas female Z. leucophrys' hormone levels did not differ between the 2 habitat types. To assess the fitness correlates of variation in hormone levels, we monitored seasonal reproductive success in one urban population and found that baseline corticosterone levels were predictive of female, but not male, reproductive success: females with higher corticosterone fledged fewer offspring. Data do not suggest a direct relationship between corticosterone levels and fitness and instead indicate an indirect relationship between hormone secretion, territory quality, body condition, and reproductive success. Females with blood parasites had lower heterophil:lymphocyte ratios, lower body condition scores, fewer mates, and fledged fewer offspring than females without parasites. In contrast, parasites did not negatively affect reproductive success in males but were associated with reduced body condition. Corticosterone levels did not differ between birds with and without parasites. In tests of all 3 of our hypotheses, we found sex-specific effects, highlighting the importance of considering sex in investigation of physiological responses to disturbance. Copyright 2007.

Constraints on, and determinants of, the annual number of breeding attempts in the multi‐brooded Black RedstartPhoenicurus ochruros

With reference to models predicting patterns of reproduction in multi‐brooded species, I analysed some of the factors potentially affecting the number of breeding attempts per season made by female Black RedstartsPhoenicurus ochrurosin the central Swiss Alps. The maximum number of successful broods per female per season was three, the median two. The proportion of females initiating only a single clutch per season varied from 16 to 58% over 10 years. Variation in the frequency of single brooding between years was positively related to the date of the onset of breeding. Egg‐laying started after a temperature‐related threshold value was crossed in April. Females frequently re‐nested before fledglings of the previous brood were independent. Short interbrood intervals were associated with triple brooding. The interbrood interval shortened during the breeding season. Intra‐individual variation in the number of breeding attempts per season was partitioned according to female age, laying date of the season's first egg (standardized in relation to the median date of first laying within a year) and the occurrence of breeding failures before the ultimate nesting attempt. However, mortality during the season often terminated breeding early, in particular among novice breeder females. Seasonal reproductive success increased linearly with each additional breeding attempt. The productivity of a breeding attempt was independent of the time in the season. Increased reproductive effort affected neither current or future survival nor reproduction of females. The reproductive patterns and trade‐offs in multi‐brooded Black Redstarts contrast in many aspects with those found in single‐brooded species. They are in accordance with models predicting that multi‐brooded species are selected to start breeding as early as possible, continue breeding for as long as conditions are suitable, and save time by overlapping broods.

Condition‐dependent nesting in bluegill sunfish Lepomis macrochirus

1. There are two prominent, nonmutually exclusive hypotheses to explain the timing of reproduction in animals: energetic constraint and adaptive behaviour. 2. We tested these hypotheses by quantifying the costs and benefits of nesting at different times in the season for male bluegill sunfish Lepomis macrochirus, a species with paternal care, in Lake Opinicon (Ontario, Canada). 3. The value of nesting at different times during the breeding season (RSb) was determined from spawning individuals as RSb = Pb x Cb x Sb x Ob, where Pb is the probability of spawning during each bout b, Cb is the expected brood size, Sb is the expected brood survivorship to 'swim-up', and Ob is the survivorship of free-swimming fry to age 1 year. 4. The results show that the value of nesting peaks during the middle of the season. However, nesting patterns varied with male condition and not all males nested at the peak. 5. Larger males, which were able to nest multiple times, first nested early in the season when overwinter survivorship of offspring and renesting opportunities later in the season were maximized. These males had the highest seasonal reproductive success. 6. Smaller males, which nested a single time, delayed nesting until the middle of the season when spawning opportunities and brood sizes were greatest. 7. These data suggest that both energetics and adaptive behaviour play roles in determining the timing of reproduction.

Reproductive skew and individual strategies: infanticide or cooperation?

Infanticide in species with shared reproduction may indicate attempts to control the degree of skew within groups. Alternatively, individuals that have done poorly in reproduction could use infanticide for hastening the next breeding attempt. Many factors influence the individual’s decision over whether it is best to cooperate or engage in destruction. We present a qualitative model incorporating kinship among adults and progeny, social status, group size and seasonality to predict behavioural options for individuals of diverse backgrounds. The social system used for the model was that of the guira cuckoo (Guira guira), a Neotropical bird that breeds communally. We suggest communal breeders utilise the best available predictors for enhancing seasonal reproductive success, with favourable consequences for lifetime inclusive fitness. Predictors rely upon parameters that change over time, including the individual’s assessment of present and future possibilities. The model produces predictions that may be tested through field observations and molecular analyses for species with similar social dynamics.

Mating system, philopatry and patterns of kinship in the cooperatively breeding subdesert mesiteMonias benschi

In the first molecular study of a member of the threatened avian family, Mesitornithidae, we used nine polymorphic microsatellite loci to elucidate parentage, patterns of within-group kinship and occurrence of extra-group paternity in the subdesert mesite Monias benschi, of southwest Madagascar. We found this cooperatively breeding species to have a very fluid mating system. There was evidence of genetic monogamy and polygynandry: of the nine groups with multiple offspring, six contained one breeding pair with unrelated helpers and three contained multiple male and female breeders with related helpers. Although patterns of within-group kinship varied, there was a strong positive relationship between group size and relatedness, suggesting that groups form by natal philopatry. There was also a strong positive correlation between within-sex and between-sex relatedness, indicating that unlike most cooperatively breeding birds, philopatry involved both sexes. In contrast to predictions of kin selection and reproductive skew models, all monogamous groups contained unrelated individuals, while two of the three polygynandrous groups were families. Moreover, although between-group variation in seasonal reproductive success was related to within-group female relatedness, relatedness among males and between the sexes had no bearing on a group's reproductive output. While kin selection may underlie helping behaviour in females, factors such as direct long-term fitness benefits of group living probably determine helping in males. Of the 14 offspring produced by fully sampled groups, at least two were sired by males from neighbouring groups: one by a breeding male and one by a nonbreeding male, suggesting that males may augment their reproductive success through extra-group paternity.

Antioxidants and condition‐dependence of arrival date in a migratory passerine

Early arrival at the breeding area after spring migration determines several fitness benefits to migratory birds, including an early start of reproduction and a greater seasonal reproductive success. Environmental conditions determine the onset of migration at the population level, while physiological costs associated with migration and imposed on individuals determine the level of asynchrony in the pattern of arrival. These costs include several physiological changes, suppression of immune response, and an increased risk of oxidation by production of free radicals due to energetically expensive activities. According to the condition‐dependent hypothesis of arrival date, only healthy individuals in prime condition can afford to arrive and thus reproduce early in the season.We investigated condition‐dependence of arrival date in male barn swallow (Hirundo rustica L.), a migratory passerine, in two years that differed in environmental condition, and the role of carotenoids in mediating arrival date. We show that male tail length, the main secondary sexual character, body condition, and hematocrit were negatively correlated with arrival date in the first year, indicating better quality of early arriving males. In the second year, better environmental conditions advanced arrival of the entire population by weeks. In this season we could show no relationship between arrival and tail length or body condition. Moreover, a lower value of sedimentation rate and a brighter colour of the red throat feathers indicated better health status of the population. Arrival date is a condition‐dependent character in barn swallows, since we found high repeatability of arrival date, lower values of carotenoids in blood and a lower depletion of carotenoids in blood shortly after arrival in early arriving males. This suggests that early arriving males either use fewer antioxidants for free radical scavenging, or they have differential access to antioxidants.

Seasonal and lifetime reproductive consequences of inbreeding in the great tit Parus major

Inbreeding depression has been hypothesized to drive the evolution of mating systems and dispersal. Some studies have shown that inbreeding strongly affects survival and/or fecundity, but other studies suggest that fitness consequences of inbreeding are less detrimental or more complex. We studied consequences of mating with a relative in a population of great tits ( Parus major ) with a high local recruitment rate. Genotypic information from microsatellite markers was used to calculate coefficients of kinship, and fitness was measured as seasonal and lifetime reproductive success. We show that mating with a relative affects seasonal reproductive success, as was found in other studies of the same species. However, these effects do not result in a lifetime fitness reduction, suggesting that individuals may have scope for avoidance of inbreeding after inbreeding depression. Several explanations are proposed as compensatory mechanisms. Although individuals are more likely to divorce after experiencing inbreeding depression, we show that divorce alone cannot explain the compensation for inbreeding depression in subsequent breeding attempts in our study. We conclude that the costs of mating with a relative in the short term do not necessarily imply lifetime fitness consequences.

Temporal change in mite abundance and its effect on barn swallow reproduction and sexual selection

Abstract The tropical fowl mite Ornithonyssus bursa parasitizing barn swallows Hirundo rustica in a Danish population demonstrated a dramatic change in abundance during 1982–2000. Prevalence of mites in nests showed a decrease from 66% in 1987 to a minimum of 1% in 1999. Two parasite manipulation experiments of barn swallow nests in 1988 and 1999 revealed a strong effect of parasites on host reproductive success in the first year (with an average reduction in seasonal reproductive success of 30% when 50 mites were added to nests as compared with controls), but only a weak effect the last year. This pattern was paralleled by a positive relationship between reduction in host reproductive success between egg laying and fledging and mite prevalence during different years of the study period. Mite abundance on adult hosts was negatively related to tail length of males (a secondary sexual character) at the peak of mite abundance in 1988, while that relationship became weaker in the beginning of the 1990s and disappeared at the end of the 1990s. Assortative mating with respect to mite loads in the 1980s also disappeared in the 1990s. Mean tail length of male hosts increased by 1.3 standard deviations during the study period because of changes in phenotype-dependent patterns of mortality outside the breeding season. This microevolutionary change in mean male phenotype of the host was accompanied by a correlated response in mite abundance. These results are consistent with the hypothesis that the host has become more resistant to the mite during the study period, and that the mite from earlier playing an important role in natural and sexual selection of the host now is of little importance.

Heterosis and outbreeding depression in descendants of natural immigrants to an inbred population of song sparrows (Melospiza melodia).

We studied heterosis and outbreeding depression among immigrants and their descendants in a population of song sparrows on Mandarte Island, Canada. Using data spanning 19 generations, we compared survival, seasonal reproductive success, and lifetime reproductive success of immigrants, natives (birds with resident-hatched parents and grandparents), and their offspring (F1s, birds with an immigrant and a native parent, and F2s, birds with an immigrant grandparent and resident-hatched grandparent in each of their maternal and paternal lines). Lifetime reproductive success of immigrants was no worse than that of natives, but other measures of performance differed in several ways. Immigrant females laid later and showed a tendency to lay fewer clutches, but had relatively high success raising offspring per egg produced. The few immigrant males survived well but were less likely to breed than native males of the same age that were alive in the same year. Female F1s laid earlier than expected based on the average for immigrant and native females, and adult male F1s were more likely to breed than expected based on the average for immigrant and native males. The performance differences between immigrant and native females and between F1s and the average of immigrants and natives are consistent with the hypothesis that immigrants were disadvantaged by a lack of site experience and that immigrant offspring benefited from heterosis. However, we could not exclude the possibility that immigrants had a different strategy for optimizing reproductive success or that they experienced ecological compensation for life-history parameters. For example, the offspring of immigrants may have survived well because immigrants laid later and produced fewer clutches, thereby raising offspring during a period of milder climatic conditions. Although sample sizes were small, we found large performance differences between F1s and F2s, which suggested that either heterosis was associated with epistasis in F1s, that F2s experienced outbreeding depression, or that both phenomena occurred. These findings indicate that the performance of dispersers may be affected more by fine-scale genetic differentiation than previously assumed in this and comparable systems.

Group breeding dramatically increases reproductive success of yearling but not older female scrubwrens: a model for cooperatively breeding birds?

Summary Many studies of cooperatively breeding birds have found no effect of group size on reproductive success, contrary to predictions of most adaptive hypotheses. A model is proposed for variation in group‐size effects: group size has a reduced effect on success when conditions for breeding are good, such as in good environmental conditions or in groups with older breeders. This hypothesis is tested with a case study of white‐browed scrubwrens Sericornis frontalis and a review of the literature. The scrubwren is a cooperatively breeding passerine with male helpers. Previous analyses revealed no effect of group size on reproductive success, but those analyses were restricted to groups with older females (Magrath & Yezerinac 1997). Here 7 years’ data are used to contrast the effect of group size on reproductive success for yearling and older females. Yearling females breeding in groups had more than double the seasonal reproductive success than those breeding in pairs, even after controlling for territory quality. However, group size still had no effect on the reproductive success of older females. Yearling females tended to survive better in groups, but older females tended to survive better in pairs, emphasizing this pattern. Yearlings breeding in pairs were more likely to be found on poor‐quality territories than those breeding in groups, exaggerating the already‐strong effect of group size on yearling success. Older females were not affected significantly by territory quality. Group size, territory quality and female age affected different components of seasonal reproductive success. Group size increased the success of individual nesting attempts, while both territory quality and female age affected the length of the breeding season, and thus the number of breeding attempts. A sample of the literature on cooperative breeders shows that group size has a larger effect on reproductive success in poorer conditions, caused either by younger, inexperienced breeders or poorer environmental conditions. Scrubwrens therefore illustrate a widespread pattern, which provides an explanation for much of the variation in group‐size effects among and within species. Clearly single estimates of group‐size effects for species can be inadequate to test ideas about the evolution of cooperative breeding.

REPRODUCTIVE SUCCESS OF WATER PIPITS IN AN ALPINE ENVIRONMENT

Abstract To understand the evolution of avian reproductive strategies it is important to assess how differences in reproductive success are related to timing of the breeding season, quality of nesting territories or breeders, or to a combination of these factors. Over three years, we studied the reproductive performance of female Water Pipits (Anthus spinoletta) in a temporally and spatially variable alpine environment. The study area covered two valley slopes that differed in the probability of nest predation, food availability, and climate. Nest predation and harsh weather were the main proximate causes of differences in female reproductive success. Because these two environmental factors were locally unpredictable, individual females could best optimize their seasonal reproductive success by choosing the “right” breeding time. The average number of young fledged per season was inversely related to the date of initial breeding and increased from females with only first attempts, through females with rep...

Relationship Between Tail Color Pattern and Reproductive Success, Mate Acquisition and Nest Predation in Rufous Bush Chats

AbstractRufous Bush Chats (Cercotrichas galactotes) show a conspicuous tail color pattern consisting of terminal white and subterminal black patches which are shown in tail display during nest defense, aggression, and courtship. Multiple linear regression of visual tail features of males showed that in the two years of study, birds with higher bilateral symmetry in the black patches attained higher seasonal reproductive success, mated earlier in the season, and their nests were less likely to be depredated. In one year, birds with greater white terminal patches also attained higher reproductive success and their nests were less likely to be depredated, and in the other year birds with longer tails paired earlier. I suggest that these tail features have an effect on reproductive success by facilitating early pairing and/or by diminishing nest predation.

RELATIONSHIP BETWEEN TAIL COLOR PATTERN AND REPRODUCTIVE SUCCESS, MATE ACQUISITION AND NEST PREDATION IN RUFOUS BUSH CHATS

Rufous Bush Chats (Cercotrichas galactotes) show a conspicuous tail color pattern consisting of terminal white and subterminal black patches which are shown in tail display during nest defense, aggression, and courtship. Multiple linear regression of visual tail features of males showed that in the two years of study, birds with higher bilateral symmetry in the black patches attained higher seasonal reproductive success, mated earlier in the season, and their nests were less likely to be depredated. In one year, birds with greater white terminal patches also attained higher reproductive success and their nests were less likely to be depredated, and in the other year birds with longer tails paired earlier. I suggest that these tail features have an effect on reproductive success by facilitating early pairing and/or by diminishing nest predation.