Multi-brooded Passerine Research Articles

Seasonal variations in gonad morphology and hypothalamic GnRH-I and GnIH in Eurasian Tree Sparrow, a multi-brooded passerine

The hypothalamic-pituitary-gonadal (HPG) axis ubiquitously regulates seasonal reproduction, following the rhythmicity of a suite of environmental cues. Birds display prominent seasonal variations in gonad size regulated by two hypothalamic peptides, gonadotropin-releasing hormone-1 (GnRH-I) and gonadotropin-inhibiting hormone (GnIH). How multi-brooded avian species adjust GnRH-I and GnIH to regulate gonadal morphology seasonally remains largely unknown. Here, we studied the variations in the hypothalamic immunoreactivity (ir) of GnRH-I and GnIH, gonadal proliferation, and apoptosis in a typical multi-brooded species, the Eurasian Tree Sparrow (Passer montanus), across the pre-breeding (PB), first breeding (FB), second breeding (SB), pre-basic molt (PM), and wintering stages (WS). Our results showed that both sexes had higher preoptic area (POA)-GnRH-I-ir but lower paraventricular nucleus (PVN)-GnIH-ir neurons during the breeding stages (FB and SB) relative to other life-history stages, with no significant differences between two broods. The testes and ovaries were significantly larger during the breeding stages. Testicular volume increased during the two broods due to anincreased diameter of seminiferous tubules. Furthermore, there were more testicular apoptotic cells in PB and WS stages than in breeding stages, and in PB stage than in PM stage. Males had higher POA-GnRH-I expression than females during the breeding stages, but both sexes had comparable PVN-GnIH expression throughout the annual cycle. Both sexes of the sparrows may undergo a similar pattern of life-history stage-dependent variation in the hypothalamic GnRH-I, GnIH, and gonadal morphology, except that during breeding stages, males may display higher expression of POA-GnRH-I relative to females. The higher expression of POA-GnRH-I-ir in breeding male sparrows may be critical for male-dependent parental care.

Context-dependent effects of yolk androgens on nestling growth and immune function in a multibrooded passerine.

Female birds may adjust their offspring phenotype to the specific requirements of the environment by differential allocation of physiologically active substances into yolks, such as androgens. Yolk androgens have been shown to accelerate embryonic development, growth rate and competitive ability of nestlings, but they can also entail immunological costs. The balance between costs and benefits of androgen allocation is expected to depend on nestling environment. We tested this hypothesis in a multibrooded passerine, the spotless starling, Sturnus unicolor. We experimentally manipulated yolk androgen levels using a between-brood design and evaluated its effects on nestling development, survival and immune function. Both in first and replacement broods, the embryonic development period was shorter for androgen-treated chicks than controls, but there were no differences in second broods. In replacement broods, androgen-treated chicks were heavier and larger than those hatched from control eggs, but this effect was not observed in the other breeding attempts. Androgen exposure reduced survival with respect to controls only in second broods. Regarding immune function, we detected nonsignificant trends for androgen treatment to activate two important components of innate and adaptive immunity (IL-6 and Ig-A levels, respectively). Similarly, androgen-treated chicks showed greater lymphocyte proliferation than controls in the first brood and an opposite trend in the second brood. Our results indicate that yolk androgen effects on nestling development and immunity depend on the environmental conditions of each breeding attempt. Variation in maternal androgen allocation to eggs could be explained as the result of context-dependent optimal strategies to maximize offspring fitness.

Manipulating grass silage management to boost reproductive output of a ground-nesting farmland bird

Grass fodder crops are attractive nesting habitats for a suite of declining farmland bird species that nest in taller grass swards. Multiple, early silage harvests cause substantial losses of nests and flightless fledglings, making this widespread crop an influential population sink in temperate farmland. We measured the effects of two simple conservation interventions (raised cutting heights and delayed mowing) designed to increase the reproductive output of a multi-brooded passerine (skylark Alauda arvensis). Annual reproductive output of independent juveniles (fecundity) was quantified using a stochastic re-nesting model that allowed us to investigate the impacts of a wide range of potential management interventions (varying cutting heights, dates and machinery) at minimal cost.Under typical silage management mean skylark fecundity was only 13–17% of the level required for metapopulation stability (the replacement rate). 12–54% of nests and 28–44% of fledglings survived a typical silage harvest with most losses caused by abandonment of nests covered by cut grass, crushing by wheels or predation soon after mowing. Delaying mowing increased fecundity, but only up to a maximum of 44% of the replacement rate. Raising cutting heights had a negligible impact on fecundity. Asynchrony between nesting attempts (due to predation, starvation and protracted delays between nesting attempts) resulted in few attempts taking place when they could benefit from the interventions. In the absence of mowing, fecundity was only 47% of the replacement rate, due to low reproductive output per nesting attempt, while simulations showed that increasing output per nest would have the largest impact on fecundity. Conservation effort should focus on providing alternative high fecundity breeding and foraging habitats at the landscape scale, to counteract silage fields’ action as a sink for skylark populations in livestock-farming areas. These conclusions are likely to apply to other multi-brooded ground-nesting species.

Yearly and Seasonal Variation of Breeding Parameters in a Declining Multi-Brooded Passerine, the Tree Sparrow

Over a five-year period we monitored breeding parameters in a colony of Tree Sparrows Passer montanus in central Spain. This multi-brooded species can raise one to three broods per season. In this study, we analyzed inter-brood variation in reproductive success to infer the existence of seasonal patterns. We also explored inter-annual variation of life-history traits, which is of particular interest in a declining species like the Tree Sparrow. In agreement with our expectation of a multi-brooded species, clutch size showed a quadratic relationship with laying date. We found that the inter-brood interval varied significantly depending on the number of breeding attempts, which suggests that the species may engage in time-saving behaviours as reported for other multi-brooded passerines. Nestlings from second broods fledged in better condition than nestlings from first and third broods. Fewer fledglings were produced in third broods than in preceding breeding attempts. The reproductive output of third broods...

Intra-seasonal changes in reproductive strategy of a multi-brooded passerine: the tree sparrow Passer montanus

In order to evaluate how a multi-brooded bird species adapts its breeding strategy during the breeding season, we investigated variations in clutch size, egg traits and sex of the final eggs in a population of the tree sparrow Passer montanus in northwestern Croatia. Of the three clutches of the season, the second was the largest and it contained the largest eggs. Furthermore, the females followed the brood survivor strategy for the second clutch, while they chose the brood reduction strategy for the first and the third clutches. These results indicate that female tree sparrows adjusted their reproductive strategy over the course of the breeding season and invested the most resources in the second clutch. We hypothesise that their decisions may serve to maximise the number of offspring that they can successfully rear in a single breeding season.

Seasonal Tradeoffs in Reproductive Investment in a Multi-Brooded Passerine

Abstract. Because investment in eggs is costly for birds, a female's body condition is expected to influence that investment. Moreover, resource availability can fluctuate by year, and older and younger females may acquire or allocate resources differently. Additionally, in multi-brooded species, females may make tradeoffs in investment in first and second clutches. Because environmental conditions often change through the breeding season and early maturity of second broods can increase females' fitness, patterns of females' allocation to each clutch may change with the season. Here, we investigate associations between females' quality (body condition and age) and pre-hatching investment (clutch size, average egg mass per clutch, and total clutch mass) in adults of the Eastern Bluebird (Sialia sialis), a multi-brooded cavity-nesting passerine. In the two years of the study, relationships differed; in 2003, females that were heavier relative to their body size produced larger eggs and invested in greater o...

Importance of climatic and environmental change in the demography of a multi-brooded passerine, the woodlarkLullula arborea

1. We examined the influence of local weather conditions on reproductive success, timing of breeding and survival in a population of a multi-brooded ground nesting passerine (woodlark Lullula arborea) over 35 years. 2. Woodlarks laid larger clutches when rainfall was low and temperature high during the egg-laying and pre-laying period. Nest success increased with higher temperatures during the nesting period. In successful nests, the number of chicks fledged per egg laid was greater when weather was drier during the brood stage. 3. Although woodlarks bred earlier in years with warmer early spring temperatures, with the onset of breeding varying by 25 days, there was no significant advance in the onset of breeding over the 35 years of study, due to considerable inter-annual variability, and no overall trend, in weather. 4. Simulation modelling of annual reproductive output demonstrated that earlier breeding could increase productivity by 23.5% in the warmest compared to the coldest year, due to birds having more nesting attempts. Other effects of weather on productivity affected breeding output to a lesser extent. 5. Effects of weather on productivity were minor compared to an increased rate of nest predation through the period of study, which reduced productivity by 49.8% by 2004 compared to 1971. 6. Turning points analysis identified three distinct demographic periods: from 1971 to 1988 the population grew slowly, during 1988-1999 the population grew rapidly, but after 1999 the population declined. Increased population growth after 1988 was associated with higher first-year survival rates (estimated using a population model). Population decline after 1999 was caused by a combination of reduced productivity (resulting from increased nest failure rates attributed to predation) and lower first-year survival rates, that appear unrelated to winter temperature. 7. Climate change (long-term changes in weather) did not explain the marked changes observed in the population trajectory over 35 years. We suggest that understanding effects of both climate and habitat change on populations is essential in predictive population modelling.

Complex interactions among temporal variables affect the plasticity of clutch size in a multi‐brooded bird

Phenotypic plasticity is a widespread phenomenon and may have important influences on evolutionary processes. Multidimensional plasticity, in which multiple environmental variables affect a phenotype, is especially interesting if there are interactions among these variables. We used a long-term data set from House Sparrows (Passer domesticus), a multi-brooded passerine bird, to test several predictions from life-history theory regarding the shape of optimal reaction norms for clutch size. The best-fit model for variation in clutch size included three temporal variables (the order of attempt within a season, the date of those attempts, and the age of the female). Clutch size was also sensitive to the quadratics of date and female age, both of which had negative coefficients. Finally, we found that the relationship between date and clutch size became more negative as attempt order increased. These results suggest that female sparrows have a multidimensional reaction norm for clutch size that matches predictions of life-history theory but also implicates more complexity than can be captured by any single model. Analysis of the sources of variation in reaction norm height and slope was complicated by the additional environmental dimensions. We found significant individual variation in mean clutch size in all analyses, indicating that individuals differed in the height of their clutch size reaction norm. By contrast, we found no evidence of significant individual heterogeneity in the slopes of several dimensions. We assess the possible mechanisms producing this reaction norm and discuss their implications for understanding complex plasticity.

Within-Season Prevalence of Extrapair Young in Broods of Double-Brooded and Mate-Faithful Eastern Phoebes (Sayornis Phoebe) in Indiana

Abstract We examined prevalence of extrapair young (EPY) between first and second broods of a multibrooded passerine, Eastern Phoebe (Sayornis phoebe). During the 1998–2000 field seasons, we conducted behavioral observations to assign social parentage to offspring in nests and then conducted paternity analysis on a subset of social families where (1) the male and female maintained their pair bond for all broods within the breeding season, and (2) adults successfully fledged their first brood and subsequently attempted a second brood within the same breeding season. We used three hypervariable microsatellite loci to document the presence and frequency of EPY in first and second brood offspring from 87 social family units where all individuals had been sampled (n = 174 broods, n = 81 social males, n = 82 social females, n = 769 offspring). Although the majority of pairs were both socially and genetically monogamous within a breeding season, 17.2% (15 of 87 families) of all families had EPY in at least one brood and we found two cases of intraspecific brood parasitism. Overall, 9.2% of all broods (16 of 174 broods) contained EPY and 5.1% of all nestlings that hatched were EPY (39 of 769 nestlings). Second broods were more likely to contain EPY than first broods (4.6% first broods with EPY [4 of 87], 13.8% second broods with EPY [12 of 87]). The total number of EPY was greater in second broods than in first broods (1.0% EPY [4 of 411 nestlings] in first broods, 9.8% EPY [35 of 358 nestlings] in second broods).

WITHIN-SEASON PREVALENCE OF EXTRAPAIR YOUNG IN BROODS OF DOUBLE-BROODED AND MATE-FAITHFUL EASTERN PHOEBES (SAYORNIS PHOEBE) IN INDIANA

Abstract We examined prevalence of extrapair young (EPY) between first and second broods of a multibrooded passerine, Eastern Phoebe (Sayornis phoebe). During the 1998–2000 field seasons, we conducted behavioral observations to assign social parentage to offspring in nests and then conducted paternity analysis on a subset of social families where (1) the male and female maintained their pair bond for all broods within the breeding season, and (2) adults successfully fledged their first brood and subsequently attempted a second brood within the same breeding season. We used three hypervariable microsatellite loci to document the presence and frequency of EPY in first and second brood offspring from 87 social family units where all individuals had been sampled (n = 174 broods, n = 81 social males, n = 82 social females, n = 769 offspring). Although the majority of pairs were both socially and genetically monogamous within a breeding season, 17.2% (15 of 87 families) of all families had EPY in at least one b...

Determinants of reproductive success in a Mediterranean multi-brooded passerine: the Black WheatearOenanthe leucura

The factors affecting individual variation in reproductive success in a multibrooded passerine, the Black WheatearOenanthe leucura, were studied during five years in a dry inland depression in SE Spain. Black Wheatear pairs initiated 1–5 breeding attempts in a season, including relayings, and managed to raise 0–3 broods and 0–13 fledglings. The onset of breeding for different pairs spanned several months. The number of breeding attempts and the proportion of young resulting in fledged young (excluding predated broods) were the best predictors of seasonal reproductive success. Clutch size showed a quadratic relationship with laying date. Female age and time of residency and indexes of parental condition such as discontinuities in feather growth or prevalence of ectoparasites had significant effects on breeding productivity. Repeatabilities of breeding performance for males, females or in territories were not significant.

Annual Productivity and Its Measurement in a Multi-Brooded Passerine, the Eastern Bluebird

Abstract Breeding and demographic parameters are examined for 434 Eastern Bluebirds (Sialia sialis) attempting 324 nests in southeastern Michigan during 1968-1977. Nesting birds spent an average of 10.4 weeks (63.9% of a 16.2-week season) in the study area. Only 154 (35.5%) of the nesting birds remained for entire breeding seasons; these season-long residents averaged 2.14 nests/season and had a higher success rate (68.4%) and presumably greater productivity (5.6 young · pair−1 · season −1) than other birds because site fidelity depends on nesting success. Although two seasonal peaks for egg-laying were observed, only 75 of 357 birds (21.0%) successfully raised two broods. Evidence is presented to suggest that birds observed for only part of a season initiated nests at the same rate while in and not in the study area, so that an average annual productivity value of 5.0 young · pair−1 · season −1 is calculated for all nesting birds from the observed success rate (57.1%) and mean length of stay in the area. Estimated average productivity of yearlings (4.3 young · pair−1 · season −1) was lower than that of adults (5.7 young · pair−1 · season −1) although nesting success rates were similar in the two age groups.