Factors affecting the probability of double brooding by Southern House Wrens

Seasonal fecundity of birds is influenced by clutch sizes and the number of successful breeding attempts during a breeding season. As such, understanding the factors that determine the decision to initiate multiple broods within a season and the consequences of this reproductive tactic is important. We examined the frequency of double brooding by Southern House Wrens (Troglodytes aedon musculus) in eastern Argentina. We analyzed inter‐ and intraseasonal variation in double brooding and evaluated the effect of weather conditions and laying date on the frequency and occurrence of this behavior. Finally, we assessed the effect of double brooding on the seasonal and lifetime productivity of female Southern House Wrens. During our 8‐year study, we found that ～43% (range = 17–83% each year) of breeding pairs attempted a second brood after successfully raising a first brood. The probability of females having a second brood was affected by the laying date of the first nesting attempt, but was independent of the number of young fledged. About 65% of females that started laying eggs before the first quarter of each breeding season produced a second brood, and this percentage decreased to ～40% after this period. In addition, variation in double‐brooding frequency among years was related to weather conditions, with the proportion of pairs double brooding increasing with increased precipitation early in the breeding season. More precipitation likely contributed to an increase in insect abundance. Although double brooding increased the seasonal and lifetime productivity of female Southern House Wrens, additional study of the survival and fate of fledglings from first and second broods is needed to assess the importance of multi‐brooding in the reproductive success of these wrens.     

Aggressive displays by male House Wrens are composed of multiple components that predict attack

Aggressive signals should predict whether the sender of the signal will attack the receiver, yet this criterion has been little studied. We conducted experiments with male House Wrens (Troglodytes aedon) in north‐central Illinois in 2009 to test the hypothesis that rates of song delivery and wing‐quivering (putative aggressive signals) signal aggressive intent. We simulated a conspecific territorial intrusion by combining playback of male song with a male taxidermic mount, predicting that these signals would be related to a male's likelihood of attacking a conspecific. All males (N = 37) sang in response to the intrusion. Males attacking the mount sang at significantly higher rates and performed significantly more wing quivers than males that did not attack. In addition, all males that attacked the mount performed wing quivers (9/9), whereas only 53.6% (15/28) of males that did not attack did so (P = 0.011). Our results are consistent with the hypothesis that both song and wing quivering indicate a signaler's aggressive intent and that these signals are likely components of a multi‐component, hierarchical display.     

Increased cuckoldry as a cost of breeding late for male house wrens (Troglodytes aedon)

One factor hypothesized to influence the reproductive behaviorof individuals is the degree to which reproductive effortsare synchronized with others in the population. We asked whetherthe timing of a pair's breeding cycle, relative to cycles ofpairs on neighboring territories, affected rates of extrapairmating over 2 years in a Wyoming population of house wrens (Troglodytes aedon). Extrapair young (identified using 5 microsatelliteloci) occurred in 74% of nests of 19 pairs whose cycles began later than cycles of one or more neighbors compared to only26% of nests of 27 pairs whose cycles began earlier than, orsimultaneously with, cycles of all neighbors. Extrapair offspringoccurred in 65% of 17 nests belonging to males who initiallysettled and began nesting early relative to neighbors but who were forced to renest late after we removed their first mates.Rates of cuckoldry were not significantly different for forced-lateand naturally late males. Our experimental approach controlledfor possible effects of male quality, clearly demonstratingan effect of timing of breeding on extrapair mating activity.     

Male song diversity and its relation to breeding success in southern house wrens Troglodytes aedon chilensis

Theory proposes an adaptive relationship between male song complexity, including large song repertoires, and improved breeding success. Evidence supporting these relationships exists but is sometimes mixed or weak. Here we provide a first comprehensive study of the relationship between male song diversity and breeding success in a non‐migratory, austral population of house wrens Troglodytes aedon chilensis breeding in Mendoza, Argentina. During a two‐year field study, we measured breeding success for a population of 62 males and recorded more than 34 000 songs from a subsample of 26 males. For the latter subsample, we tested for correlations between six measures of song diversity and four canonical measures of annual breeding success. Males that sang with greater overall syllable type diversity and that had larger song repertories paired with females that bred earlier and laid more eggs over the course of the breeding season. However, these males also showed lower levels of immediate song type diversity, as measured by the Levenshtein distance between successive songs. We discuss implications for the evolution of song complexity in this exceptionally widespread species and the selective mechanisms that might influence song complexity in resident populations in the Neotropics compared to migratory populations in the northern hemisphere.     

Climate warming induced a stretch of the breeding season and an increase of second clutches in a passerine breeding at its altitudinal limits

The increase in the average air temperature due to global warming has produced an early onset of the reproduction in many migratory birds of the Paleartic region. According to the “mismatch hypothesis” this response can lead to a decrease in the breeding output when the conditions that trigger the departure from the wintering areas do not match the availability of food resources in the breeding ground. We used 653 brooding events registered during the period 1991–2013 to investigate the link between climatic variables and individual breeding performance of a partially migratory passerine, the Rock Sparrow Petronia petronia, breeding at the altitude limit of its distribution. The laying date (LD) of the earliest first clutch was associated with local spring (minimum) temperatures but did not show a significant trend during the period considered. The LD of the latest first clutch had a positive and statistically significant trend, unrelated to local covariates and resulting in a longer breeding season (∼1.5 days/year). A longer breeding season allowed birds to produce more second clutches, which proportion increased from 0.14 to 0.25. The average breeding success was also positively correlated with the average temperature in July and with the duration of the breeding season. Contrary to expectations, the most important climate-dependent effect was a stretch of the breeding season due to a significant increase of the LD of the latest first-clutches rather than an earlier breeding onset. We show how climate changes act on bird populations through multiple paths and stress the need to assess the link between climatic variables and several aspects of the breeding cycle.     

Lack of predator‐odor detection and avoidance by a songbird,the House Wren

ABSTRACT Recent studies suggest that songbirds have a better sense of smell than initially suspected. Work is now focused on determining how birds use their sense of smell to enhance survival and reproduction. One question is whether birds use smell to detect and avoid predators. We examined the reaction of House Wrens (Troglodytes aedon) to the odor of a potential predator in their nests. On two different days of the nestling stage, we placed papers infused with the urine and anal scent gland material of a mustelid (American mink, Neovison vison), a neutral odoriferous substance (cologne, garlic, or vinegar), or water in nest boxes. The proportion of individuals that hesitated to enter nest boxes after first arrival did not differ significantly between treatments on either day. We also found no significant differences on either day in the time it took wrens to first enter nest boxes, time spent in nest boxes after first entry, the propensity to stay in nest boxes and brood young, or latency to return to nest boxes after first exposure to treatments. Our results suggest that House Wrens either did not detect or did not respond to foreign odors in nest cavities, including the odor of a mustelid predator. In a similar study ( Amo et al. 2008 . Functional Ecology 22: 289–293), adult Blue Tits (Cyanistes caeruleus) were less likely to enter nest boxes that contained the odor of a mustelid. One explanation for this difference is that Blue Tits may have a better sense of smell than House Wrens. Alternatively, or additionally, Blue Tits may be inherently (or as result of experience) more prone than House Wrens to avoid unusual odors or, specifically, the odor of mustelid predators in their nests. Additional studies are needed to determine the extent to which songbirds use their sense of smell to detect and avoid nest predators.     

Temperature‐correlated shifts in the timing of egg‐laying in House Finches Haemorhous mexicanus

Although temperature‐correlated shifts in the timing of egg‐laying have been documented in numerous bird species, the vast majority of species examined to date have been those that breed in Europe and have an animal‐based diet during breeding. However, given that the timing of breeding can be driven, either in the proximate or in the ultimate sense, by seasonal fluctuations in food availability, the relationship between temperature and laying may differ with diet. Here, we report on patterns of reproductive timing in House Finches Haemorhous mexicanus, a North American species that breeds on a primarily seed‐based diet. Analysing nest records from House Finches in California spanning more than a century, we found that egg‐laying occurred significantly earlier in warmer springs. We also found that although the timing of egg‐laying does not show long‐term changes in most of California, in the hottest region of the state (the southeast desert basin) it has advanced significantly.     

Associations between distance to forest and spatial and temporal variation in abundance of key peatland breeding bird species

Capsule Negative forest edge effects were detected for Willow Ptarmigan (Red Grouse) Lagopus lagopus and Dunlin Calidris alpina.

Aims To investigate the effects of distance to forest on the abundance and changes in abundance of four key peatland breeding bird species, and to measure changes in predatory bird numbers, in the peatlands of northern Scotland.

Methods Bird surveys were carried out in 2000 at 34 plots, covering 197 km² of peatland, and 80 forestry point‐count sites, first surveyed in 1988. Habitat data were also collected in 2000. We used multi‐model inference to investigate the associations between forest distance and other habitat variables, and the abundance, and changes in abundance, of four bird species of economic or conservation importance: Red Grouse, European Golden Plover Pluvialis apricaria, Dunlin and Common Greenshank Tringa nebularia.

Results There was strong evidence that distance to forest was negatively associated with Dunlin abundance and changes in Red Grouse abundance, but only weak evidence for negative associations with Golden Plover abundance and changes in Dunlin abundance. There was no evidence of a forest distance effect on Greenshank. Among predatory birds, there were no significant increases either on peatland plots or in new forestry plantations.

Conclusions This study provides evidence that, for a given habitat quality, Dunlin densities are lower, and Red Grouse declines more likely, near to forest edges, but weak evidence only that Dunlin declines are more likely, and Golden Plover abundance lower, near to forests. These results suggest that for at least two key peatland breeding birds, forest removal is likely to benefit birds breeding on adjacent unafforested peatland.     

Climatic effects on the breeding phenology and reproductive success of an arctic-nesting goose species

Climate warming is pronounced in the Arctic and migratory birds are expected to be among the most affected species. We examined the effects of local and regional climatic variations on the breeding phenology and reproductive success of greater snow geese ( Chen caerulescens atlantica ), a migratory species nesting in the Canadian Arctic. We used a long-term dataset based on the monitoring of 5447 nests and the measurements of 19 234 goslings over 16 years (1989–2004) on Bylot Island. About 50% of variation in the reproductive phenology of individuals was explained by spring climatic factors. High mean temperatures and, to a lesser extent, low snow cover in spring were associated with an increase in nest density and early egg-laying and hatching dates. High temperature in spring and high early summer rainfall were positively related to nesting success. These effects may result from a reduction in egg predation rate when the density of nesting geese is high and when increased water availability allows females to stay close to their nest during incubation recesses. Summer brood loss and production of young at the end of the summer increased when values of the summer Arctic Oscillation (AO) index were either very positive (low temperatures) or very negative (high temperatures), indicating that these components of the breeding success were most influenced by the regional summer climate. Gosling mass and size near fledging were reduced in years with high spring temperatures. This effect is likely due to a reduced availability of high quality food in years with early spring, either due to food depletion resulting from high brood density or a mismatch between hatching date of goslings and the timing of the peak of plant quality. Our analysis suggests that climate warming should advance the reproductive phenology of geese, but that high spring temperatures and extreme values of the summer AO index may decrease their reproductive success up to fledging.     

Climate change and the risks associated with delayed breeding in a tropical wild bird population

There is growing evidence of changes in the timing of important ecological events, such as flowering in plants and reproduction in animals, in response to climate change, with implications for population decline and biodiversity loss. Recent work has shown that the timing of breeding in wild birds is changing in response to climate change partly because individuals are remarkably flexible in their timing of breeding. Despite this work, our understanding of these processes in wild populations remains very limited and biased towards species from temperate regions. Here, we report the response to changing climate in a tropical wild bird population using a long-term dataset on a formerly critically endangered island endemic, the Mauritius kestrel. We show that the frequency of spring rainfall affects the timing of breeding, with birds breeding later in wetter springs. Delays in breeding have consequences in terms of reduced reproductive success as birds get exposed to risks associated with adverse climatic conditions later on in the breeding season, which reduce nesting success. These results, combined with the fact that frequency of spring rainfall has increased by about 60 per cent in our study area since 1962, imply that climate change is exposing birds to the stochastic risks of late reproduction by causing them to start breeding relatively late in the season.     

Spatial and temporal variation of phenological growing season and climate change impacts in temperate eastern China

Using phenological and normalized difference vegetation index (NDVI) data from 1982 to 1993 at seven sample stations in temperate eastern China, we calculated the cumulative frequency of leaf unfolding and leaf coloration dates for deciduous species every 5 days throughout the study period. Then, we determined the growing season beginning and end dates by computing times when 50% of the species had undergone leaf unfolding and leaf coloration for each station year. Next, we used these beginning and end dates of the growing season as time markers to determine corresponding threshold NDVI values on NDVI curves for the pixels overlaying phenological stations. Based on a cluster analysis, we determined extrapolation areas for each phenological station in every year, and then implemented the spatial extrapolation of growing season parameters from the seven sample stations to all possible meteorological stations in the study area. Results show that spatial patterns of growing season beginning and end dates correlate significantly with spatial patterns of mean air temperatures in spring and autumn, respectively. Contrasting with results from similar studies in Europe and North America, our study suggests that there is a significant delay in leaf coloration dates, along with a less pronounced advance of leaf unfolding dates in different latitudinal zones and the whole area from 1982 to 1993. The growing season has been extended by 1.4–3.6 days per year in the northern zones and by 1.4 days per year across the entire study area on average. The apparent delay in growing season end dates is associated with regional cooling from late spring to summer, while the insignificant advancement in beginning dates corresponds to inconsistent temperature trend changes from late winter to spring. On an interannual basis, growing season beginning and end dates correlate negatively with mean air temperatures from February to April and from May to June, respectively.     

Flexibility in the timing of post‐breeding moult in passerines in the UK

Higher temperatures resulting from climate change have led to predictions that the duration of the breeding season of many temperate bird species may be changing. However, the extent to which breeding seasons can be altered will also depend on the degree of flexibility in processes occurring at other points in the annual cycle. In particular, plasticity in the timing of post‐breeding moult (PBM) could facilitate changes in the timing of key events throughout the annual cycle, but little is known about the level of within‐ and between‐species plasticity in PBM. As part of the British Trust for Ornithology (BTO) Ringing Scheme, many ringers routinely record moult scores of flight feathers, and these can be used to provide information on the annual progression of PBM for a range of species. Here we use ringing data to investigate patterns of PBM in 15 passerines, as well as data from the BTO Nest Record Scheme to relate these differences to the timing of breeding of these species across the UK. We find considerable variation in both the mean start (19 May–29 July) and duration (66–111 days) of PBM between species, but find no evidence that species starting PBM later in the season complete it any faster. However, there is considerable within‐species variation in PBM, particularly for multi‐brooded species; PBM starts later and is completed in less time when the duration of the breeding season (difference between first and last nests) is longer. This implies that a later end to breeding can be compensated for by faster PBM, and that advances in breeding could lead to earlier and slower PBM. Our findings suggest that adaptation of PBM in response to climate‐mediated changes in the timing and duration of the breeding season is possible. However, the requirement to complete PBM prior to migration or the onset of winter might constrain the extent to which breeding seasons can lengthen, especially for later nesting species.     

Sexual dimorphism and synchrony of breeding: variation in polygyny potential among populations in the common brushtail possum, Trichosurus vulpecula

Male-biased sexual dimorphism in both size and body mass isa common characteristic of many polygynous mammals and is oftenattributed to sexual selection favoring large males. The degreeof dimorphism is thought to be related to the potential forsome males to monopolize access to estrous females, which isin turn related to the distribution of receptive females inspace and time. In the present study, we investigated the relationshipbetween the temporal distribution of breeding females and thedegree of mass dimorphism among 11 populations of the commonbrushtail possum from northern Australia. Breeding patternsvaried from complete aseasonality in some populations to a seasonalconcentration of births within 2 or 3 months in others. We predictedthat in populations in which mating opportunities were distributedthroughout the year, dominant males would be able to monopolizeaccess to larger numbers of estrous females than in populationsin which matings were more seasonal, and in such populations,large body size in males would be favored. We found that dimorphismwas related to seasonality of breeding, being greatest in populationswith a more aseasonal pattern. Mean body mass of male possumsalso decreased with increasing population density. Populationdensity may influence the degree of breeding synchrony withinpopulations, particularly in locations with a more seasonalclimate. The present study is the first to demonstrate plasticityin mass dimorphism in response to local variation in the synchronyof breeding in a mammal species.     

Monitoring and managing genetic variation in group breeding populations without individual pedigrees

The genetic management of captive populations to conserve genetic variation is currently based on analyses of individual pedigrees to infer inbreeding and kinship coefficients and values of individuals as breeders. Such analyses require that individual pedigrees are known and individual pairing (mating) can be controlled. Many species in captivity, however, breed in groups due to various reasons, such as space constraints and fertility considerations for species living naturally in social groups, and thus have no pedigrees available for the traditional genetic analyses and management. In the absence of individual pedigree, such group breeding populations can still be genetically monitored, evaluated and managed by suitable population genetics models using population level information (such as census data). This article presents a simple genetic model of group breeding populations to demonstrate how to estimate the genetic variation maintained within and among populations and to optimise management based on these estimates. A numerical example is provided to illustrate the use of the proposed model. Some issues relevant to group breeding, such as the development and robustness evaluation of the population genetics model appropriate for a particular species under specific management and recording systems and the genetic monitoring with markers, are also briefly discussed.     

Limited phenological and pollinator-mediated isolation among selfing and outcrossing Arabidopsis lyrata populations

Transitions from outcrossing to selfing have been a frequent evolutionary shift in plants and clearly play a role in species divergence. However, many questions remain about the initial mechanistic basis of reproductive isolation during the evolution of selfing. For instance, how important are pre-zygotic pre-pollination mechanisms (e.g. changes in phenology and pollinator visitation) in maintaining reproductive isolation between newly arisen selfing populations and their outcrossing ancestors? To test whether changes in phenology and pollinator visitation isolate selfing populations of Arabidopsis lyrata from outcrossing populations, we conducted a common garden experiment with plants from selfing and outcrossing populations as well as their between-population hybrids. Specifically, we asked whether there was isolation between outcrossing and selfing plants and their between-population hybrids through differences in (1) the timing or intensity of flowering; and/or (2) pollinator visitation. We found that phenology largely overlapped between plants from outcrossing and selfing populations. There were also no differences in pollinator preference related to mating system. Additionally, pollinators preferred to visit flowers on the same plant rather than exploring nearby plants, creating a large opportunity for self-fertilization. Overall, this suggests that pre-zygotic pre-pollination mechanisms do not strongly reproductively isolate plants from selfing and outcrossing populations of Arabidopsis lyrata.     

Interannual variation in reproductive phenology in a riverine fish assemblage: implications for predicting the effects of climate change and altered flow regimes

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Spatial variation in breeding phenology at small spatial scales: A stochastic effect of population size

Spatial variation in phenology can occur at small spatial scales over which individuals can disperse or forage within one generation. Previous studies have assumed that variations in phenological peaks are caused by differences in abiotic environmental characteristics. However, environments should generally be similar among local habitats over small spatial scales. When the local population size is small, the phenological peak of the local population should be strongly affected by the variation in timing expressed by individuals. If a regional population consists of small local subpopulations (e.g., a metapopulation), the stochastic processes regulated by population sizes may explain the spatial variation in phenology. In this study, we quantitatively evaluated the extent of the spatial and annual variations in the breeding phenology of the forest green tree frog, Rhacophorus arboreus habiting a small area (<10 km²). The spatial variation in phenological peaks among 25 breeding sites was large over 6 years. This spatial variation was not explained by differences in air temperature or water depth. Randomization tests revealed that a large portion of the spatial variation could be explained by differences in population size, without considering site-specific factors. Annual variations in phenological peaks tended to be greater for smaller populations. These results imply that the stochastic process might have caused the spatial and annual variations in the phenological peaks of R. arboreus observed in the study region. Understanding spatiotemporal variation in phenology determined by stochastic process would be important to better predict interspecific interactions and (meta)population dynamics at small spatial scales.