Balance between site fidelity and habitat preferences in colony site selection by herons and egrets

Habitat selection in avian species is a hierarchical process driven by different factors acting at multiple scales. Habitat preferences and site fidelity are two main factors affecting how colonial birds choose their breeding locations. Although these two factors affect how colonial species choose their habitats, previous studies have only focused on one factor at a time to explain the distribution of species at regional scales. Here we used 28 yr of colony location data of herons and egrets around Ibaraki prefecture in Japan in order to analyze the relative importance of habitat preferences and colony site fidelity for selecting breeding locations. We used Landsat satellite images together with a ground survey‐based map to create land‐use maps for past years and determine the habitats surrounding the herons and egrets colonies. Combining the estimated colony site fidelity with the habitat data, we used a random forest algorithm to create habitat selection models, which allowed us to analyze the changes in the importance of those factors over the years. We found high levels of colony site fidelity for each year of study, with its relative importance as a predictor for explaining colony distribution increasing drastically in the most recent five years. The increase in collective site fidelity could have been caused by recent changes in the population size of grey herons Ardea cinerea, a key species for colony establishment. We observed a balance between habitat preferences and colony site fidelity: habitat preferences were a more powerful predictor of colony distribution until 2008, when colony site fidelity levels were lower. Considering changes in the relative importance of these factors can lead to a better understanding of the habitat selection process and help to analyze bird species’ responses to environmental changes.     

Breeding site fidelity and natal philopatry in the Redshank Tringa totanus

This paper presents the results of a study carried out on breeding Redshank in the Ribble Marshes, Lancashire, England.
Redshank tend to return to the same breeding area year after year. There was no detectable sex bias in return rates. Experienced birds were more site faithful than inexperienced birds, with previously successful birds exhibiting the highest degree of breeding site fidelity. Older, more experienced birds were more successful at hatching eggs than inexperienced birds.
Breeding dispersal was the same both within and between years. Faithful pairs and males nesting with a new mate dispersed significantly shorter distances than females nesting with a new partner. Dispersal distances in female Redshank were affected by breeding success: unsuccessful females, nesting with a new mate, dispersed significantly farther than successful females. A pair's breeding success influenced the following year's mate fidelity. However, other factors such as overwintering survival and date of return may also have influenced mate fidelity.
Redshank were highly faithful to their natal area; a high proportion of birds that survived post-fledging mortality returned to breed in their area of birth. No sex bias in natal dispersal was detected. Approximately 50% of Redshank breed in their first year of life.     

Movements of radio-tagged Grey Herons Ardea cinerea during the breeding season in a large pond area

This paper describes the strategies of resource utilization in the course of the breeding season by five radio-tagged Grey Herons Ardea cinerea. The seasonal changes in exploitation of the environment by two breeding adults, one non-breeding adult and two non-breeding first-year birds were studied from March to August 1982, near Zonhoven in Belgium. Two adult breeding birds could be followed continuously from the end of March until the middle of June. During the first month they explored an extended area all around the colony, but each concentrated its search in a specific direction. From the end of April until the beginning of June, most probably from egg-hatching until the end of breeding activities, each bird spent a very large proportion of its time at a particular feeding site, from which other herons were actively excluded. In the first part of June they again visited different sites, each maintaining its preferred direction. From the middle of June onwards they seemed to have left the fish-pond area. The pattern of movements of the first-year birds differed markedly from that of the breeding adults. In April, although both non-breeding and breeding birds explored large areas, only the areas used by non-breeders were centred on the colony. From the end of April onwards, probably after general egg-hatching in the colony, the non-breeders very rarely revisited the colony, and from May till August their ranges became more and more restricted to very small areas at an increasing distance from the colony. They were never observed defending particular sites. The results are discussed with regard to recent speculations about the evolution of colonies as an adaptation for the exploitation of food resources. Breeding herons seem to explore a large part of the environment during incubation and defend a particular site while feeding their young. Choice of feeding site by non-breeding birds may be influenced by the site defence of the breeding birds. Non-breeding birds exploit a large area when breeding birds occupy feeding territories. Perhaps they are forced to forage in less suitable places at this time. Colonies might have evolved as a strategy to minimize effort in resource esploitation as, especially at the beginning of the breeding season, the colony could act as an assembly point in the exploration of the environment. However, its importance as an assembly point diminishes in the course of the season, as non-breeding birds no longer visit the colony and adults defend territories.     

Intermittent breeding in Cory's Shearwater Calonectris diomedea of Selvagem Grande, North Atlantic

Every year, 10% of the breeding population of Cory's Shearwater Calonectris diomedea of Selvagem Grande, between the Canaries and Madeira (30̀09'N, 15̀52'W), fail to breed. These "sabbatical" periods can last up to 7 years but typically last 1 year in 58% of the cases, with an average of 1.7 years. Both sexes are involved, and most are young breeding birds. The frequency and duration of the absences decrease with the increase of breeding experience. During the year preceding the absence, the breeding success, mate fidelity and nest site fidelity of the breeding birds are the same as those of their sabbatical congeners. During the sabbatical absence, the former mate is also absent in just less than half of the cases. Of those present, two-thirds are at the same nest site and one-third at another nest site. On the return of the "missing" birds, the fidelity both to the former mate and the former nest site is low, and more so if the length of the absence has been over 1 year, because the former mate and the former nest site are then seldom available. Divorce is frequent and the breeding success is low. Comparisons with other Procellariiformes reveal few differences in the intermittent breeding except for the proportions involved, which are six times greater for some species than for others.     

Site use and fidelity in the Common Guillemot Uria aalge

The site fidelity of 470 colour-ringed Common Guillemots Uria aalge with at least 1 year of breeding experience was followed on the Isle of May from 1982 to 1993. On average, 85.7% of birds recorded breeding at a site in any year were present at the same site in the following season. Of those which did not retain their site, 35% had moved to another site, 25% were nonbreeders and 40% were not seen. Site- fidelity of birds which returned to the colony the next year was 91%. There were no significant age or sex effects, but there were significant (and unexplained) year and area effects. Most birds which changed sites moved less than 2 m. Some birds which obtained a new site improved their nesting success, but many others became nonbreeders; it is speculated that the former chose to move site, whilst the latter had been evicted.     

Sources of variation in breeding-ground fidelity of mallards (Anas platyrhynchos)

Generalizations used to support hypotheses about the evolutionof fidelity to breeding areas in birds include the tendencyfor fidelity to be greater in adult birds than in yearlings.In ducks, in contrast to most bird species, fidelity is thoughtto be greater among females than males. Researchers have suggestedthat fidelity in ducks is positively correlated with pond availability.However, most estimates of fidelity on which these inferences have been based represent functions of survival and recapture—resighting probabilities in addition to fidelity. We applied the modelingapproach developed by Burnham to recapture and band recoverydata of mallard ducks to test the above hypotheses about fidelity.We found little evidence of sex differences in adult philopatry,with females being slightly more philopatric than males inone study area, but not in a second study area. However, yearlingfemales were more philopatric than yearling males in both study areas. We found that adults were generally more philopatricthan yearlings. We could find no relationship between fidelityand pond availability. Our results, while partially supportingcurrent theory concerning sex and age differences in philopatry,suggest that adult male mallards are more philopatric thanonce thought, and we recommend that other generalizations aboutphilopatry be revisited with proper estimation techniques.     

Breeding site fidelity of blue-winged teal in South Dakota

Assumptions about breeding site fidelity (i.e., fidelity) in blue-winged teal (Spatula discors) are based on limited recapture data and analytic techniques. We banded female blue-winged teal (n = 12,543) from 2003 to 2014 in a 3,800-ha sample area in north-central South Dakota, USA, and used a Bayesian hierarchical modeling approach combining live recapture and dead recovery data to predict probabilities of fidelity, survival, recapture, and reporting. We explored sources of variation including time, annual wet area on the landscape, age, and nest survival, and compared our results to other dabbling ducks that nest in the Prairie Pothole Region, a critically important breeding area for waterfowl in central North America. We found annual estimates of fidelity ranging from 0.20 to 0.91, with mean values of 0.62 and 0.67 for hatch year birds and after hatch year birds, respectively. Our findings indicate that environmental factors may cause blue-winged teal to return to breeding sites more frequently than previously assumed. © The Wildlife Society, 2019     

Dispersal, interpatch movements, and survival in a shrubland breeding bird community

ABSTRACT Dispersal events can affect the distribution, abundance, population structure, and gene flow of animal populations, but little is known about long‐distance movements due to the difficulty of tracking individuals across space. We documented the natal and breeding dispersal of shrubland birds among 13 study sites in a 1000 km² area in southeastern Ohio. In addition, we radio‐marked and tracked 37 adult males of one shrubland specialist, the Yellow‐breasted Chat (Icteria virens). We banded 1925 juveniles and 2112 adults of nine shrubland species from 2002 to 2005. Of these, 33 (1.7%) juveniles were encountered in subsequent years (2003–2006) as adults (natal dispersal) and 442 (20.9%) birds initially banded as breeding adults were re‐encountered in subsequent years (breeding dispersal). Apparent survival of juvenile shrubland birds on their natal patches was 0.024 (95% CI 0.016–0.036). After accounting for the probability of detection, we found that 21% of birds banded as juveniles and recaptured as adults returned to their natal patches, whereas 78% of adult birds showed fidelity to the patch where they were originally captured. Moreover, natal dispersers tended to move farther than breeding dispersers (corrected natal median = 1.7 km ± 0.37; corrected breeding median = 0.23 km ± 0.10). We used our estimates of natal dispersal and annual apparent survival to estimate true survival at 0.11 (95% CI 0.07–0.18) for juveniles in their first year. However, this estimate was only applicable for birds dispersing within 7 km of their natal patches. Interpatch movements of radio‐marked Yellow‐breasted Chats were not uncommon, with 13 of 37 males located in more than one habitat patch. Overall, we observed low natal philopatry, but high adult site fidelity for shrubland birds in our study area. Considering the frequency of short‐distance movements observed (median = 531 m, range = 88–1045 m), clustering of patches within 1 km might facilitate use of shrubland habitat.     

Breeding sites and winter site fidelity of Piping Plovers wintering in The Bahamas,a previously unknown major wintering area

Most of the known wintering areas of Piping Plovers (Charadrius melodus) are along the Atlantic and Gulf coasts of the United States and into Mexico, and in the Caribbean. However, 1066 threatened/endangered Piping Plovers were recently found wintering in The Bahamas, an area not previously known to be important for the species. Although representing about 27% of the birds counted during the 2011 International Piping Plover Winter Census, the location of their breeding site(s) was unknown. Thus, our objectives were to determine the location(s) of their breeding site(s) using molecular markers and by tracking banded individuals, identify spring and fall staging sites, and examine site fidelity and survival. We captured and color‐banded 57 birds in January and February 2010 in The Bahamas. Blood samples were also collected for genetic evaluation of the likely subspecies wintering in The Bahamas. Band re‐sightings and DNA analysis revealed that at least 95% of the Piping Plovers wintering in The Bahamas originated on the Atlantic coast of the United States and Canada. Re‐sightings of birds banded in The Bahamas spanned the breeding distribution of the species along the Atlantic coast from Newfoundland to North Carolina. Site fidelity to breeding and wintering sites was high (88–100%). Spring and fall staging sites were located along the Atlantic coast of the United States, with marked birds concentrating in the Carolinas. Our estimate of true survival for the marked birds was 0.71 (95% CI: 0.61–0.80). Our results indicate that more than one third of the Piping Plover population that breeds along the Atlantic coast winters in The Bahamas. By determining the importance of The Bahamas to the Atlantic subspecies of Piping Plovers, future conservation efforts for these populations can be better focused on where they are most needed.     

Movement Patterns in a Partial Migrant: A Multi-Event Capture-Recapture Approach

Partial migration is a pervasive albeit poorly studied phenomenon by which some individuals of a population migrate while others are residents. It has tremendous consequences on seasonal variations of population size/structure and therefore management. Using a multi-event capture-mark-recapture/recovery (CMR) approach, we assessed seasonal site occupancy, survival and site fidelity of a partially migratory diving duck, the Common pochard (Aythya ferina), in an area potentially including both local breeders and winter visitors. The modelling exercise indeed discriminated two different categories of individuals. First, locally breeding females which had a probability of being present in our study area during winter of 0.41. Females of this category were found to be more faithful to their breeding site than males (breeding site fidelity probabilities of 1 and 0.11, respectively). The second category of birds were winter visitors, which included adults of both sexes, whose probability of being present in the study area during the breeding season was nil, and young of both sexes with a 0.11 probability of being present in the area during the breeding season. All wintering individuals, among which there was virtually no locally breeding male, displayed a high fidelity to our study area from one winter to the next (0.41–0.43). Estimated annual survival rates differed according to age (adults 0.69, young 0.56). For both age classes mortality was higher during late winter/early spring than during summer/early winter. Our study is among the first to show how and under which conditions the multi-event approach can be employed for investigating complex movement patterns encountered in partial migrants, providing a convenient tool for overcoming state uncertainty. It also shows why studying patterns of probability of individual presence/movements in partial migrants is a key towards understanding seasonal variations in numbers.     

Local breeding experience and the reproductive performance of Tree Swallows

ABSTRACT The potential advantages of repeated breeding at a particular location should improve reproductive performance in long‐lived species of birds. However, for short‐lived species, natural selection should favor individuals that most quickly develop competency in reproduction. Therefore, we hypothesized that local breeding experience beyond the first breeding attempt at a particular location would have little effect on subsequent reproductive performance of Tree Swallows (Tachycineta bicolor), a species where about 50% of adults breed only once in their lives. We tested this hypothesis using data collected from Tree Swallows in Michigan from 1993 to 2002. Because we were specifically interested in examining the effects of local breeding experience on reproductive performance, we restricted our analyses to after‐second‐year (ASY) females and their mates that we first encountered as breeders. Consistent with our hypothesis, we found no relationship between repeated local breeding experience and the reproductive performance of ASY female Tree Swallows and their mates as measured by clutch size and number of fledged young. However, pairs with more combined total local experience tended to lay eggs earlier in the season. These results suggest that Tree Swallows may benefit from breeding site fidelity, not because repeated local experience improves reproductive performance as measured by the production of fledglings, but because returning individuals acquire nest cavities earlier and are able to begin breeding earlier, providing time to renest in case of early nest failure.     

Mate fidelity in monogamous birds: a re-examination of the Procellariiformes

Mate retention is classically considered advantageous for reproduction in monogamous birds: because of their low fecundity, long-lived species should show the highest year-to-year mate fidelity. However, this hypothesis remains controversial: several studies have found no correlation between mate fidelity and longevity, possibly because they did not control for potential confounding factors on each of these parameters, and one study found a negative correlation in the Procellariiformes (albatrosses and petrels). We re-examined the relations between mate fidelity and longevity, and between mate fidelity and site fidelity, in this group, using our data on 13 species and data from the literature, and after eliminating confounding factors. Procellariiformes are the most long lived of birds despite important interspecific variation in body size, and they show strong mate fidelity and bear high costs of divorce. All species lay only one egg, and the most long lived breed biennially. Because large organisms live longer than small ones and their reproductive effort is lower, we had to control for breeding frequency and body size. Mate fidelity and adult life expectancy were positively correlated, regardless of whether we controlled for these two parameters. We also evaluated whether mate fidelity was related to site fidelity. Biennial albatrosses show high mate fidelity, but low nest fidelity, although they are extremely faithful to a small area around their previous nest. After controlling for body size, adult life expectancy and breeding frequency, we found no correlation between mate fidelity and site fidelity. Because divorce is costly and mate retention advantageous in Procellariiformes, we suggest that mate fidelity does not passively result from site fidelity in these species. Rather, site fidelity would be a means for pairs to reunite, with sites serving as meeting points. Copyright 2003 The Association for the Study of Animal Behaviour. Published by Elsevier Science Ltd. All rights reserved.      

Repopulation and colonization by birds in the Agmon Wetland,Israel

Lake Hula and its surrounding wetland in northern Israel were drained in the late 1950s and the dried wetlands were transformed into a diverse agricultural region with a 0.3 km2 nature reserve. A portion of the extinct Hula wetland was re-flooded in April 1994 by constructing a small lake, Agmon, and 90 km of canals. The purposes of this study were (a) to document the re-population and colonization of the new Agmon wetland by birds after its flooding, (b) to evaluate bird species richness in this new wetland in comparison to that in a nearby mature Hula Nature Reserve, and, (c) to investigate if the species originally present in the Hula Valley before the drainage had been re-established. The new lake has succeeded in attracting a large variety of water birds to the newly formed habitats, especially ducks, egrets and herons, plovers, waders and snipes. The distribution of bird species among the different habitats was not random. The northern section of the lake, which is shallow and has an open shore, had the largest number of species during 1995 and 1996 and was preferred by plovers, waders and snipes. A large roosting and breeding colony of thousands of egrets and herons was formed in the dense cattails ( Typha domingensis) in the southern section of the lake. Unlike the nearby Hula Nature Reserve, the new wetland lacks a large seasonally flooded area and is less attractive for feeding and breeding plovers, waders and stilts. The new wetland also has very little muddy area without vegetation and attracts few of the species that regularly feed in this habitat in the reserve. The new wetland enlarges the area of only a few of the habitats found in the nearby reserve and therefore attracts fewer species than it might otherwise. Recommendations for management of the new wetland include increased diversity of habitats, restriction of human activities and optimization of conflicts that have arisen between the needs of the wetland and those of nearby agriculture.     

Mate fidelity and breeding site tenacity in a monogamous sandpiper, the black turnstone

We examined the relationship between mate fidelity and breeding site tenacity during a 5-year study of the black turnstone, Arenaria melanocephala, a socially monogamous sandpiper breeding in subArctic Alaska. We tested the predictions of several hypotheses regarding the incidence of divorce and the benefits of fidelity to mate and breeding site. Interannual return rates to the breeding grounds (88% for males, 79% for females) were among the highest yet recorded for any scolopacid sandpiper, and 88% of returning birds nested on their previous year's territory. The annual divorce rate was only 11%, and mate fidelity was significantly linked to fidelity to territory but independent of sex and year. Males arrived in spring significantly earlier than their mates and interannual fidelity was influenced by the relative timing of arrival of pair members. Reunited pairs had significantly higher fledging success than new pairs formed after death or divorce. The incidence of divorce was unrelated to reproductive success the previous year, although birds nested significantly further away after failure than after a successful nesting attempt. Sightings of marked individuals suggested that members of pairs do not winter together, and breeding site tenacity provides a mechanism through which pair members can reunite. We reject the 'incompatibility' hypothesis for divorce in turnstones, and our data contradict predictions of the 'better option' hypothesis. Alternatively, we propose the 'bet-hedging' hypothesis to explain the occurrence of divorce, which transpires when an individual pairs with a new mate to avoid the cost of waiting for a previous mate to return. Such costs can include remaining unmated, if the former mate has died, or experiencing lower reproductive success because of delayed breeding. Copyright 2000 The Association for the Study of Animal Behaviour.     

Foraging differences between white and dark morphs of the Pacific Reef Heron Egretta sacra

Among the species of diurnal herons (Ardeinae) showing light-dark colour polymorphism in plumage, colour phase is age-related in one species, closely associated with geography in three species, and found in most populations in three closely related species of reef herons. In Pacific Reef Herons Egretta sacra white-phased birds sought prey by a flight, land, and freeze hunting style in breaking surf, while dark birds pursued prey by actively walking or running on reef flats. On Mangaia, in the southern Cook Islands, more white-phased birds used the windward side of the island and more dark-phased birds used the lee side. On Rarotonga, 204 km from Mangaia, reef herons foraged almost exclusively in shaded streams and no entirely white-phased bird was encountered. These results provide the first evidence of differences in hunting techniques associated with colour morph and only the second observation of differences in habitat use by white- and dark-phased herons at single localities. As such they support Murton's (1971) idea that colour polymorphism serves herons in their role as predators. For reasons discussed in the text such differences are more expected in reef herons than in most other colour-polymorphic herons.     

Winter Fidelity and Apparent Survival of Lesser Snow Goose Populations in the Pacific Flyway

Abstract The Beringia region of the Arctic contains 2 colonies of lesser snow geese (Chen caerulescens caerulescens) breeding on Wrangel Island, Russia, and Banks Island, Canada, and wintering in North America. The Wrangel Island population is composed of 2 subpopulations from a sympatric breeding colony but separate wintering areas, whereas the Banks Island population shares a sympatric wintering area in California, USA, with one of the Wrangel Island subpopulations. The Wrangel Island colony represents the last major snow goose population in Russia and has fluctuated considerably since 1970, whereas the Banks Island population has more than doubled. The reasons for these changes are unclear, but hypotheses include independent population demographics (survival and recruitment) and immigration and emigration among breeding or wintering populations. These demographic and movement patterns have important ecological and management implications for understanding goose population structure, harvest of admixed populations, and gene flow among populations with separate breeding or wintering areas. From 1993 to 1996, we neckbanded molting birds at their breeding colonies and resighted birds on the wintering grounds. We used multistate mark-recapture models to evaluate apparent survival rates, resighting rates, winter fidelity, and potential exchange among these populations. We also compared the utility of face stain in Wrangel Island breeding geese as a predictor of their wintering area. Our results showed similar apparent survival rates between subpopulations of Wrangel Island snow geese and lower apparent survival, but higher emigration, for the Banks Island birds. Males had lower apparent survival than females, most likely due to differences in neckband loss. Transition between wintering areas was low (<3%), with equal movement between northern and southern wintering areas for Wrangel Island birds and little evidence of exchange between the Banks and northern Wrangel Island populations. Face staining was an unreliable indicator of wintering area. Our findings suggest that northern and southern Wrangel Island subpopulations should be considered a metapopulation in better understanding and managing Pacific Flyway lesser snow geese. Yet the absence of a strong population connection between Banks Island and Wrangel Island geese suggests that these breeding colonies can be managed as separate but overlapping populations. Additionally, winter population fidelity may be more important in lesser snow geese than in other species, and both breeding and wintering areas are important components of population management for sympatric wintering populations.     

Adult male chimpanzees inherit maternal ranging patterns

Space use often correlates with reproductive success [1, 2]. Individual site fidelity is ubiquitous across a variety of taxa, including birds, mammals, insects, and reptiles [3-9]. Individuals can benefit from using the same area because doing so affords access to known resources, including food and/or breeding sites. The majority of studies on site fidelity have focused upon strictly territorial species in which individuals range in well-defined, exclusive areas (e.g., [4, 9]). By comparison, the transient groups that define fission-fusion species allow for considerable flexibility in individual space use. Although there is evidence that individual space use can influence reproductive success [2], relatively little is known about individual ranging patterns in fission-fusion species. Here, we investigate three potential correlates of male site fidelity (age, habitat quality, and maternal space use) in wild chimpanzees (Pan troglodytes). We found that when alone, each male preferentially concentrated his space use near the area where his mother ranged when he was dependent. We suggest that solitary ranging allows males to avoid direct competition with conspecifics and that foraging in familiar areas maximizes foraging efficiency. These results highlight the importance of male foraging strategies in a species in which male ranging is typically explained in terms of mating access to females.     

广西防城7种鹭类混群繁殖的空间生态位研究

2002年3~8月对广西防城万鹤山营巢的鹭类繁殖种群进行了调查研究,结果表明:万鹤山栖息有大白鹭(Egretta alba)、中白鹭(Egretta intermedia)、白鹭(Egretta garzetta)、黄嘴白鹭(Egretta eulophotes)、牛背鹭(Bubulcus ibis)、池鹭(Ardeda bacchus)、夜鹭(Nycticorax nycticorax)7种鹭类种群。除黄嘴白鹭为均匀分布之外,其他6种均为成群分布。鹭类在万鹤山上营巢繁殖具有明显的水平分布和垂直分布现象。对影响鹭类混群繁殖时空间分布的因素及各种群间的相互关系进行了探讨。     

Is mate fidelity related to site fidelity? A comparative analysis in Ciconiiforms

We tested for an association between divorce rate and site fidelity in 42 avian species belonging to the order Ciconiiforms, using comparative methods that account for the influences of phylogenetic relationships on the data. Our methods enabled us to detect evidence of correlated evolution and provided information on the temporal ordering of evolutionary changes in these two variables. We found a significant correlation between divorce rate and site fidelity, indicating that species with little or no site fidelity are more likely to divorce. Our data suggest that the coupled evolution of divorce and site fidelity can be summarized by three major events. The first event corresponds to a transition from species showing high divorce rate and low or no site fidelity to species that tended to reuse the same nests over consecutive breeding seasons. This was followed by a transition towards higher mate fidelity, with the preservation of pair bonds over consecutive breeding attempts. In a third stage, divorce rate and the rate of site fidelity varied, independently of each other. We discuss our results within the context of the ancestor species and the past environments in which the traits originated, and address the importance of the potential for individual recognition in shaping the observed patterns of covariation between mate fidelity and site fidelity in Ciconiiforms. Copyright 2000 The Association for the Study of Animal Behaviour.     

Conceptual Revision and Synthesis of Proximate Factors Associated with Age‐Related Improvement in Reproduction

Improvement in reproductive performance with age, up to the point of senescence, is a predominant pattern among vertebrates. Predictions from life‐history theory provide a powerful framework for understanding the evolutionary basis of these patterns. However, based on the growing number of publications on this topic, there is increased interest in understanding the proximate causes of age‐related improvements in reproductive performance (ARIRP). A formal conceptual framework through which factors related to ARIRP can be examined is lacking. Here, we establish hypotheses with testable predictions for social and ecological factors, including resource quality, mate fidelity, site fidelity, prior breeding experience, and changes in ability to attract mates. We use this conceptual framework to review 55 empirical studies published (between 1900 through 2013) on avian species as birds have the greatest representation in empirical studies of ARIRP. Our synthesis revealed that tests of the breeding experience hypothesis are most prevalent in the literature, whereas tests of the site fidelity hypothesis are least prevalent. Overall, the role of increased mate attraction with age seems to be an important predictor of ARIRP, whereas changes in resource quality with age show the least support among published studies. Because many studies suffered from small sample sizes and did not control for confounding variables, we suggest experimental methodologies for teasing apart hypotheses in empirical investigations and offer statistical approaches for longitudinal datasets. From an ultimate perspective, we also highlight the role of life‐history variation, in shaping within‐individual improvements. Future work should employ a standardized framework to study patterns of ARIRP, as set forward here, to allow for more quantitative comparison of results across studies.