Subsequent Breeding Success Research Articles

Year-round carryover effects are driven by migration phenology for Hirundo rustica (Barn Swallow) wintering in West Africa

Abstract Recently, population declines have been reported for many migratory birds. Because of complex life cycles, determining the causes for such declines is often difficult. Thus, migratory birds are of special conservation interest. We studied the migratory behavior of Hirundo rustica (Barn Swallow) tagged with solar geolocators and determined carryover effects during the entire annual cycle from one breeding season to the next. We used a partial least squares path model (PLS-PM) to disentangle migratory and breeding events that occur in chronological order. In addition, we controlled for broad environmental conditions in the wintering grounds (NDVI and latitude) and the specific molting habitat (δ13C). We did not find a carryover effect from reproduction investment in the attachment year to breeding success in the subsequent year. Individuals that invested more in reproduction departed earlier from the breeding colonies, but this in turn did not affect the onset of autumn migration. Thus, the premigratory period should be acting as a buffer stage counteracting any previous carryover effects from reproduction investment. On the other hand, we found a long-lasting domino effect from the onset of autumn migration to subsequent breeding success, consistent with the notion of a migratory race. Specifically, individuals which started earlier in the autumn migration arrived earlier to the wintering grounds, started earlier in the spring migration arrived earlier to the breeding colonies, and had a higher breeding success. We highlight that the premigratory period (i.e., the time elapsed between departure from breeding areas and the onset of autumn migration) should be important for the life cycle of migratory species, but it has been frequently overlooked.

Does provision of supplementary food to grey partridges Perdix perdix help their over-winter survival on upland hill farms in northern England?

Grey partridge populations in the UK have declined dramatically since 1970. These birds are mainly associated with lowland cereal farms, but they are also found on marginal hill farms in northern England where they frequent rough grasslands created by low-intensity sheep farming. Here, important populations remain, but the availability of winter food, particularly in years with prolonged snow appears a major limiting factor. To investigate whether food shortages in winter limit grey partridge survival, we experimentally tested whether we could improve their survival by increasing the provision of supplementary food within five study plots, each paired with a control, over two consecutive winters. Grey partridges found and used feeding stations, with discovery time on average 12 days earlier in the second winter. The frequency of hopper use also increased on four of the five fed plots in the second winter. We found no differences in an index of over-winter survival nor subsequent breeding success in relation to the feeding treatment. However, the study coincided with two mild winters with little snow and the provision of supplementary food may be more important in more severe winters with prolonged snow cover. Grey partridges readily used feed hoppers and we recommend their provision to provide emergency food sources in severe winter weather whilst longer-term land-use based solutions are sought.

COVID19-induced reduction in human disturbance enhances fattening of an overabundant goose species

Overabundant species can have major impacts on their habitat and induce trophic cascades within ecosystems. In North America, the overabundant greater snow goose (Anser caerulescens atlanticus) has been successfully controlled through special spring hunting regulations since 1999. Hunting is a source of mortality but also of disturbance, which affects the behavior and nutrient storage dynamics of staging snow geese. In 2020, the lockdown imposed by the COVID19 pandemic reduced hunting activity during their migratory stopover in Québec by at least 31%. This provided a unique opportunity to assess the effects of a sudden reduction in hunting disturbance on geese. We used long-term data on body mass combined with movement data from GPS-tracked birds in 2019 and 2020 to assess the effects of the 2020 lockdown on the spring body condition and behavior of greater snow geese. Body condition was higher in 2020 than in all years since the inception of spring hunting in 1999, except for 2019. However, in 2020 geese reached maximal body condition earlier during the staging period than in any other year and reduced by half time spent feeding in highly profitable but risky agricultural habitat in late spring compared to 2019. Although our study was not designed to evaluate the effects of the lockdown, the associated reduction in disturbance in 2020 supports the hypothesis that hunting-related disturbance negatively affects foraging efficiency and body condition in geese. Since spring body condition is related to subsequent breeding success, the lockdown could increase productivity in this overabundant population.

The effects of geolocators on return rates, condition, and breeding success in Common Sandpipers Actitis hypoleucos

ABSTRACT Capsule: Fitting geolocators to Common Sandpipers Actitis hypoleucos did not affect their return rates, return dates, body condition or reproductive success, but did cause leg injuries in some individuals. Aims: To investigate the effect of fitting geolocators to Common Sandpipers on their return rates and timing, the condition in which they return and their subsequent breeding success. Methods: We fitted geolocators to colour-ringed Common Sandpipers and monitored them throughout the breeding seasons prior to migration and following return from their wintering grounds. We then compared return rate, return date, change in body condition, hatching success, and fledging success between birds with and without the tags. We also fitted a number of smaller geolocators to wintering individuals in Africa and compared their return rates with a control group. Results: We found no significant differences between birds with and without geolocators in any of the variables measured. However, several individuals fitted with the larger tags were found to have incurred leg injuries. Conclusion: Our study highlights the need for complete transparency when reporting the effects of geolocators and shows the importance of continuous monitoring of individuals when carrying out tracking studies.

Trade-offs between age-related breeding improvement and survival senescence in highly polygynous elephant seals: Dominant males always do better.

Life history trade-off theory predicts that current reproduction can negatively affect survival and future reproduction. Few studies have assessed breeding costs for males of polygynous species compared to females, despite substantial variation in breeding success among individual males (e.g. subordinate cf. dominant breeders). Specifically, differentiating between the cost of attending breeding seasons, and the additional cost of successfully securing and mating females is lacking. We investigated whether trade-offs are present in the highly polygynous male southern elephant seal (Mirounga leonina) using 34-years of individual-level data. We compare age-specific survival, recruitment and future breeding success probabilities of pre-breeders (males yet to recruit) and breeders (subordinate and dominant social ranks) using multievent models. Pre-breeders and breeders of overlapping ages had similar survival probabilities, suggesting that there was no attendance cost for early recruits. In addition, the probability of recruiting as a dominant breeder never exceeded recruitment probability as a subordinate breeder of the same age. Therefore, older pre-breeders that delayed attendance costs generally did not improve their breeding success (probability of being dominant) at recruitment more than younger recruits. Rather, recruitment age may be a function of individual quality, with lower quality individuals requiring more time to socially mature. When comparing subordinate and dominant breeders, we found clear evidence for survival senescence, with subordinate breeders having a higher baseline mortality. In contrast, age-specific future breeding success (probability of being dominant at t+1) increased with age, with dominant breeders maintaining higher subsequent breeding success than subordinate breeders. The opposite trends in survival and future breeding success for both subordinate and dominant breeders may indicate a lifetime, population-level trade-off. However, we found no evidence to suggest that being a dominant breeder consecutively (and having a higher accumulated breeding cost) accelerated the rate of senescence when compared to individuals that were previously subordinate. Thus, males experienced actuarial senescence regardless of social rank, with dominant (and possibly high quality) breeders showing a reduced trade-off between survival and future breeding success. We make several novel contributions to understanding polygynous male life histories and southern elephant seal demography.

Reproductive Performance, Mate Fidelity and Nest Cavity Fidelity in Red-Billed Tropicbirds Phaethon aethereus mesonauta on St. Eustatius, Caribbean Netherlands

Mate choice and nest cavity selection are directly linked to reproductive performance in seabirds, and disruption of these can result in breeding failure. The Red-billed Tropicbird Phaethon aethereus mesonauta breeds on inaccessible and remote islands, nesting primarily in natural rock cavities. I examined the relationship between reproductive performance and mate and nest cavity fidelity on St. Eustatius from 2012 to 2016, corresponding to four successive breeding seasons. The majority of nest failures occurred during the incubation stage. Pairs that failed in their first breeding attempt and laid a replacement clutch were more likely to be faithful to their mate and nest cavity within and between seasons than pairs that bred successfully. Only two replacement clutches (3.8%) were laid after the loss of a chick in the first breeding attempt, whereas the remaining 50 replacement clutches (96.2%) were laid after the loss of an egg. The stage at which pairs split had no influence on mate or nest cavity retention the following season. There were no significant differences in the weight or morphological measurements of chicks from pairs that retained their nest mate and/or cavity and those that switched. The results of this study suggest that switching nest mate or nest cavity does not necessarily improve subsequent breeding success among Red-billed Tropicbirds on St. Eustatius.

Age-dependent carry-over effects in a long-distance migratory bird

Migratory birds usually respond to climate change by modifying breeding and/or wintering areas, as well as by reproducing earlier. In addition, changes in winter habitat use or breeding phenology could have important carry-over effects on subsequent breeding success. Here, we studied age- and sex-dependent carry-over effects from wintering to the breeding stage of a small aerial insectivorous long-distance migratory bird, the barn swallows (Hirundo rustica) breeding in Denmark during 1984–2013. First, we used stable isotope analyses combined with ringing recoveries to identify wintering areas. Second, we found that environmental conditions as inferred by Normalized Difference Vegetation Index (NDVI) have improved at the wintering grounds. Third, we used confirmatory path analysis to quantify the indirect effect of winter conditions on subsequent breeding success. Males delayed onset of breeding and raised fewer fledglings in the first brood when ecological conditions during the previous winter improved. This response was age dependent, since yearlings did not respond to this environmental cue but the response was increasingly stronger as males aged. Females showed a similar response to winter conditions, although not statistically significant. These results highlight the importance of studying carry-over effects within the context of climate change, especially in relation to age of individuals.

Memory Performance Influences Male Reproductive Success in a Wild Bird

Despite decades of comparative research, how selection shapes the evolution of cognitive traits remains poorly understood [1-3]. Several lines of evidence suggest that natural selection acts on spatial memory in food-caching species [3-6]. However, a link between reproductive fitness and spatial memory ability has yet to be demonstrated in any caching species [1, 3, 6]. Here, we show that memory performance influences reproductive success differentially for males and females in a caching songbird, the New Zealand robin (Petroica longipes). Males' memory performance in a spatial task during winter influenced their subsequent breeding success; individuals with more accurate performance produced more fledglings and independent offspring per nesting attempt. Males with superior memory performance also provided an increased proportion of large prey items to chicks in the nest and spent less time flying while foraging and provisioning. No such effects were found for females. Previous research reveals that trade-offs may constrain selection and act to maintain variation in cognitive traits [7]. The gender dimorphism in the reproductive benefits of robin memory performance suggests an additional role for divergent selection between the sexes in constraining runaway selection on male memory ability [8], ultimately maintaining variation in this cognitive trait.

Effect of weather conditions on the spring migration of Eurasian Woodcock and consequences for breeding

Migration is a critical period of time with fitness consequences for birds. The development of tracking technologies now allows researchers to examine how different aspects of bird migration affect population dynamics. Weather conditions experienced during migration are expected to influence movements and, subsequently, the timing of arrival and the energetic costs involved. We analysed satellite‐tracking data from 68 Eurasian Woodcock Scolopax rusticola fitted with Argos satellite tags in the British Isles and France (2012–17). First, we evaluated the effect of weather conditions (temperature, humidity, wind speed and direction, atmospheric stability and visibility) on migration movements of individuals. Then we investigated the consequences for breeding success (age ratio) and brood precocity (early‐brood ratio) population‐level indices while accounting for climatic variables on the breeding grounds. Air temperature, wind and relative humidity were the main variables related to migration movements, with high temperatures and northward winds greatly increasing the probability of onward flights, whereas a trend towards greater humidity over 4 days decreased the probability of movement. Breeding success was mostly affected by climatic variables on the breeding grounds. The proportion of juveniles in autumn was negatively correlated with temperature in May, but positively correlated with precipitation in June and July. Brood precocity was poorly explained by the covariates used in this study. Our data for the Eurasian Woodcock indicate that, although weather conditions during spring migration affect migration movements, they do not have a major influence on subsequent breeding success.

Costs of breeding are rapidly buffered and do not affect migratory behavior in a long-lived bird species.

Life history theory states that individual fitness in one stage of life is conditioned by what occurred in previous stages. In migratory species, reproductive effort during breeding has often been found to influence body condition, molt schedule, self-provisioning and migration of individuals in subsequent seasons (i.e., carryover effects of breeding). However, there is a current uncertainty in understanding how long-distance migrants trade off among such energy-demanding activities (i.e., breeding, molting and migrating). To provide evidence to the field, we experimentally reduced the parental effort of a long-lived Procellariform, the Cory's shearwater (Calonectris borealis), by inducing failure at the incubation stage. Treatment and control birds were tracked during their subsequent migration by means of light-level and immersion loggers and sampled for six specific feathers (molted at different periods along the migratory cycle) upon the recovery of the loggers 1 yr later. Feathers were used to perform stable isotope analysis (SIA) and determine corticosterone levels (CORT). By these means, we evaluated the effect of breeding effort on migratory strategy, at-sea activity patterns, molt patterns, and levels of stress experienced by birds along the non-breeding period. We did not detect any difference between birds in the induced failure group and successful breeders in terms of spatio-temporal distribution: all birds shared common foraging areas throughout the study period and the timing of major phenological events did not differ. Failed birds significantly advanced their molt, as revealed by SIA and flying activity patterns. The stress levels of failed birds, inferred through CORT concentrations in feathers, were found to be consistently lower than in successful breeders, through the end of the breeding to the non-breeding period. Thus, we provide robust evidence that the costs of reproduction can be physiologically mediated from the breeding to the non-breeding period through molting schedules and CORT levels. However, we failed to detect clear effects on migratory behavior or subsequent breeding success, suggesting that costs of breeding in long-lived species may be rapidly buffered during the post-breeding period, as would be expected from life history theory.

Predatory risk increased due to egg‐brooding in Armadillidium vulgare (Isopoda: Oniscidea)

AbstractCost of reproduction is associated with a reduction in subsequent survival or future breeding success. A decrease in survival rate of parents during or after reproduction reduces the probability of their future reproduction. However, few studies have demonstrated such survival costs to parents. Females of Armadillidium vulgare hold their eggs in a marsupium and brood these until the young hatch. Caring for eggs in a marsupium seems to place a large burden on brooding females, and it restricts their predator avoidance behaviour. As such, costs of care may increase the mortality rates of brooding females. To reveal the costs of parental care, we examined the effects of egg brooding on behaviour and predation risk. Egg‐brooding females decreased speed of locomotion and rolling duration, and were killed by predators at a higher rate. Our results indicate that egg brooding in A. vulgare has costs in the form of predation risk.

Environmental conditions during winter predict age- and sex-specific differences in reproductive success of a trans-Saharan migratory bird

Previous studies have linked winter habitat with subsequent breeding phenology and physical condition of migratory birds, but few have found delayed effects of winter habitat on subsequent reproductive success. The aim of this study was to test if African winter habitat is related to subsequent reproductive success of house martins (Delichon urbicum) breeding at a colony in Spain. We measured stable isotope (δ2H, δ13C, δ15N) values from feathers moulted in West Africa and used confirmatory path analysis to test if isotopic values of winter-grown feathers were related to reproductive success through the mediation of breeding phenology and body condition. We conducted separate analyses for males, females and age classes (yearlings vs ≥ 2 years old). Experienced males wintering in habitats of higher rainfall (as inferred from lower feather δ2H values) were in better body condition and produced more offspring during the subsequent breeding season. In contrast, we did not find any effect of winter habitat on reproductive success of young males or females. These findings provide evidence consistent with a complex causal link between winter habitat quality and subsequent breeding success of long-distance migratory songbirds.

Multi-colony tracking reveals spatio-temporal variation in carry-over effects between breeding success and winter movements in a pelagic seabird

Carry-over effects, whereby events in one season have consequences in subsequent seasons, have important demographic implications. Although most studies examine carry-over effects across 2 seasons in single populations, the effects may persist beyond the following season and vary across a species’ range. To assess potential carry-over effects across the annual cycle and among populations, we deployed geolocation loggers on black-legged kittiwakes Rissa tridactyla at 10 colonies in the north-east Atlantic and examined relationships between the timing and destination of migratory movements and breeding success in the year of deployment and subsequent season. Both successful and unsuccessful breeders wintered primarily in the north-west Atlantic. Breeding success affected the timing of migration, whereby unsuccessful breeders departed the colony earlier, arrived at the post-breeding and main wintering areas sooner, and departed later the following spring. However, these patterns were only apparent in colonies in the south-west of the study region. Furthermore, the effect of breeding success was stronger on migration timing in the first part of the winter than later. Timing of migratory movements was weakly linked to subsequent breeding success, and there was no detectable association between breeding success in the 2 seasons. Our results indicate temporal structure and spatial hetero - geneity in the strength of seasonal interactions among kittiwakes breeding in the north-east Atlantic. Variable fitness consequences for individuals from different colonies could have important implications for population processes across the species’ range and suggest that the spatio-temporal dynamics of carry-over effects warrant further study.

Breeding success, mate-fidelity and nest-site fidelity in Red-tailed Tropicbirds (Phaethon rubricauda) on Christmas Island, Indian Ocean

Disruption of pair-bonds and switching nest-site are associated with breeding failure in many seabirds. Both strategies can prevent repetition of poor performance with a low-quality mate or at a poor-quality nesting site. In the Red-tailed Tropicbird (Phaethon rubricauda), the relationship between mate-fidelity, nest-site fidelity and reproductive performance is poorly understood. We therefore examined this relationship in Red-tailed Tropicbirds, using data collected on Christmas Island in the Indian Ocean from 1984 to 1986, corresponding to three successive breeding seasons. Birds showed strong between-season mate-fidelity, despite previous breeding failure, and subsequent breeding success in birds faithful to their mate was significantly higher than in pairs that bred together for the first time, indicating that mate-fidelity may outweigh the costs of disruption of pair-bonds. Although switching of nest-site was more likely to occur after previous breeding failure, it did not increase subsequent breeding success, indicating that nest-site switching may not be advantageous in Red-tailed Tropicbirds on Christmas Island. Although effects of age, dispersal rates to inaccessible parts of the island and adult survival were not examined in this study, our results provide a valuable basis for the evaluation of population dynamics of Red-tailed Tropicbirds on Christmas Island.

Habitat Use and Body Mass Regulation among Warblers in the Sahel Region during the Non-Breeding Season.

Migratory birds face significant challenges across their annual cycle, including occupying an appropriate non-breeding home range with sufficient foraging resources. This can affect demographic processes such as over-winter survival, migration mortality and subsequent breeding success. In the Sahel region of Africa, where millions of migratory songbirds attempt to survive the winter, some species of insectivorous warblers occupy both wetland and dry-scrubland habitats, whereas other species are wetland or dry-scrubland specialists. In this study we examine evidence for strategic regulation of body reserves and competition-driven habitat selection, by comparing invertebrate prey activity-density, warbler body size and extent of fat and pectoral muscle deposits, in each habitat type during the non-breeding season. Invertebrate activity-density was substantially higher in wetland habitats than in dry-scrubland. Eurasian reed warblers Acrocephalus scirpaceus occupying wetland habitats maintained lower body reserves than conspecifics occupying dry-scrub habitats, consistent with buffering of reserves against starvation in food-poor habitat. A similar, but smaller, difference in body reserves between wet and dry habitat was found among subalpine warblers Sylvia cantillans but not in chiffchaffs Phylloscopus collybita inhabiting dry-scrub and scrub fringing wetlands. Body reserves were relatively low among habitat specialist species; resident African reed warbler A. baeticatus and migratory sedge warbler A. schoenobaenus exclusively occupying wetland habitats, and Western olivaceous warblers Iduna opaca exclusively occupying dry habitats. These results suggest that specialists in preferred habitats and generalists occupying prey-rich habitats can reduce body reserves, whereas generalists occupying prey-poor habitats carry an increased level of body reserves as a strategic buffer against starvation.

Effects of the bioaccumulative polybrominated diphenyl ether flame retardant congener BDE-47 on growth, development, and reproductive success in zebra finches.

This study investigated the effects of the polybrominated diphenyl ether congener, 2,2',4,4'-tetrabromodiphenyl ether (BDE-47) on the growth and development, and subsequent breeding success of exposed zebra finches (Taeniopygia guttata). Using oral dosing procedures and treatments adjusted by weight, we treated newly hatched chicks daily for the first 20-days-post-hatch (dph) with varying treatments of BDE-47 (0, 5, 50, and 500ng/gbw/day). Weight and tarsal measurements were monitored from hatch to 90dph, but no differences were observed between treatment groups at any age. Treated females that reached sexual maturity were mated with untreated males; however, again no treatment effects were observed on breeding success. Analysis of tissue samples at 21dph did indicate that debromination of BDE-47 had occurred resulting in BDE-28 and BDE-17 metabolites.

Bioeconomic factors of beef heifer maturity to consider when establishing criteria to optimally select and/or retain herd replacements.

Understanding the biology of heifer maturity and its relationship to calving difficulty and subsequent breeding success is a vital step in building a bioeconomic model to identify optimal production and profitability. A limited dependent variable probit model is used to quantify the responses among heifer maturities, measured by a maturity index (MI), on dystocia and second pregnancy. The MI account for heifer age, birth BW, prebreeding BW, nutrition level, and dam size and age and is found to be inversely related to dystocia occurrence. On average there is a 2.2% increase in the probability of dystocia with every 1 point drop in the MI between the MI scores of 50 and 70. Statistically, MI does not directly alter second pregnancy rate; however, dystocia does. The presence of dystocia reduced second pregnancy rates by 10.67%. Using the probability of dystocia predicted from the MI in the sample, it is found that on average, every 1 point increase in MI added 0.62% to the probability of the occurrence of second pregnancy over the range represented by the data. Relationships among MI, dystocia, and second pregnancy are nonlinear and exhibit diminishing marginal effects. These relationships indicate optimal production and profitability occur at varying maturities, which are altered by animal type, economic environment, production system, and management regime. With these captured relationships, any single group of heifers may be ranked by profitability given their physical characteristics and the applicable production, management, and economic conditions.

Fidelity at the frontier: divorce and dispersal in a newly colonized raptor population

Divorce and breeding dispersal are key life history parameters that can be influenced by, and in turn have an influence on, the structure of populations. Variation in these parameters in small populations can potentially play an important role in the colonization of new areas, yet to date there has been little empirical investigation of this process. We studied the circumstances surrounding divorce in a newly established population of black sparrowhawks, Accipiter melanoleucus, on the Cape Peninsula, South Africa over an 11-year period between 2001 and 2012. Divorce was more likely following breeding failure and individuals that divorced and dispersed improved their subsequent breeding success. Territory quality had no influence on the frequency of divorce, and dispersing individuals did not move to territories of higher quality. During the study period the population size increased approximately three-fold, but because the range expanded, nest density did not increase significantly. In the first half of the study (2001–2006), divorce rates were low (4%) compared with rates previously reported for raptors and other birds. In the latter half (2007–2012) divorce rates were 14%. Although there was weak support for a difference in divorce rates between these two periods there was no evidence that divorce rates varied with population size or nesting density. Our results suggest that adaptive hypotheses (‘better option’ or ‘incompatibility’) best explain patterns of divorce in this expanding population and that potential feedbacks between divorce and population processes were unlikely to have played an important role during the growth of this recently established population.

Early growth, dominance acquisition and lifetime reproductive success in male and female cooperative meerkats

In polygynous species, variance in reproductive success is higher in males than females. There is consequently stronger selection for competitive traits in males and early growth can have a greater influence on later fitness in males than in females. As yet, little is known about sex differences in the effect of early growth on subsequent breeding success in species where variance in reproductive success is higher in females than males, and competitive traits are under stronger selection in females. Greater variance in reproductive success has been documented in several singular cooperative breeders. Here, we investigated consequences of early growth for later reproductive success in wild meerkats. We found that, despite the absence of dimorphism, females who exhibited faster growth until nutritional independence were more likely to become dominant, whereas early growth did not affect dominance acquisition in males. Among those individuals who attained dominance, there was no further influence of early growth on dominance tenure or lifetime reproductive success in males or females. These findings suggest that early growth effects on competitive abilities and fitness may reflect the intensity of intrasexual competition even in sexually monomorphic species.

Management of waterfowl shooting during periods of severe weather in the UK

During prolonged periods of severe weather waterfowl habitats are affected by snow or ice. Recreational users of the countryside can move waterbirds off prime feeding areas, potentially resulting in reductions in body condition, at a time when energy reserves are key to overwinter survival and subsequent breeding success. Over the last 30 years the British Association for Shooting and Conservation has been closely involved, along with the government and other conservation NGOs, in developing and implementing a criteria–driven process for defining severe weather and managing waterfowl shooting during it in order to minimise unnecessary disturbance to overwintering waterbirds. The system works well and is widely respected and applauded by conservation agencies. There are increasing efforts to bring more countryside activities, including dog walking, bird watching/ringing and other wetland users, into the system so as to reduce further unnecessary waterfowl disturbance during difficult winter weather.