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Telomere length (TL) is known to covary with a suite of physiological traits involved in energy balances that may influence breeding success. Thus, TL may be an indicator of individual quality, influencing mate choice and breeding strategies. In the Brown Booby (Sula leucogaster), a long-lived seabird, we investigated in a total of 72 pairs whether TL may indicate the individual physiological phenotype by examining how it relates to mitochondrial DNA copy number (mtDNAcn) and corticosterone (CORT) levels. Then, we tested if TL is associated with mating patterns by looking for covariation with skin coloration (a condition-dependent sexual trait), whether there is assortative mating by TL, and if the degree of TL similarity between partners influences an individual’s likelihood of changing mates between reproductive seasons. Because environmental conditions can have important effects on the condition and reproductive strategies of individuals, the study was performed in 2 colonies with contrasting breeding conditions. We found that TL was positively related to mtDNAcn (but not CORT levels), suggesting that individuals with shorter telomeres may have a reduced mitochondrial density. TL was reflected in sexual coloration, but only in the colony with good breeding conditions. There was positive assortative mating by TL; however, the degree of assortative mating was unrelated to the probability of mate change, which greatly varied between the 2 colonies. Our results suggest that TL is associated with the physiological phenotype of individuals and their breeding patterns. Importantly, contrasting environmental conditions influenced the link between TL and sexual coloration and the propensity of individuals to change mate, highlighting the importance of environmental variation on mating patterns. [ABSTRACT FROM AUTHOR]

Social monogamy is the most common social mating system in birds. However, the persistence of pair bonds between breeding seasons varies among species, populations and individuals. Understanding fitness causes and consequences of mate change is critical for understanding population dynamics and the evolution of social monogamy. We used 12 years of data from Scopoli's shearwater breeding population to estimate mate change probabilities and test whether they affect the probabilities of (1) skipping breeding, (2) apparent survival and (3) breeding success. Widowing was the most common cause of mate change, with more males changing mates at least once in their lives than females. Females' probability of skipping a breeding season increased significantly just before pairing with a new partner. Also, we found that females' apparent survival, but not males', might increase after mate change. A possible explanation is that a longer adult life expectancy of females after mate change could at least partially offset the cost of skipping breeding. We found no relation between mate change and breeding success. Our study suggests that the costs and benefits of mate fidelity may be sex specific in this species. Future research on this topic should focus on the effects of mate change on each sex's lifetime reproductive success, which we could not address specifically in this study. Future studies will hopefully be able to delve deeper into how mate change, caused by divorce or widowhood, shifts the balance of reproduction or survival, determining lifetime reproductive success. • We investigated the fitness consequences of mate change. • Widowing was the most common cause of mate change. • Females that changed mates increased survival and skipping breeding probabilities. • Future studies should focus on sex-differential effects of mate change on fitness. [ABSTRACT FROM AUTHOR]

Abstract Background Information pertaining to nest-site fidelity and breeding dispersal over successive years can help to better our understanding of how birds respond to nest predation. Methods By using mist nets and tracking the color banded individuals, we investigated nest-site fidelity and breeding dispersal by Common Tailorbirds (Orthotomus sutorius) throughout a year and between successive years in 2017–2018. Results The present study showed that Common Tailorbirds could produce up to four clutches per breeding season. When multiple broods were produced within a year, breeding pairs remained together, and the nest rebuilding rate was up to 92.2%, with only four cases (7.8%) in which birds reused their old nests. The dispersal distance between the nests during multiple breeding was found to be 10.0 ± 10.5 m, and nest-site fidelity within the same year was 90.0%. By the second year of breeding, 76.2% of individuals remained in the original breeding pairs, while for those that did switch partners, the females remained in the nest from the previous year and paired with new males. The dispersal distance between years was 26.5 ± 41.9 m, and nest-site fidelity between different years was 80.1%. There was no significant difference between within-year and between-year dispersal distances. Moreover, there was no significant difference in the dispersal distance of rebuilt nests between birds that had experienced nest predation and those that had not. Conclusions Our findings suggest that Common Tailorbirds maintain a high degree of fidelity to mates and nest-sites, and nest predation had no significant effect on territorial changes or breeding dispersal distance between each breeding attempt.

Territory acquisition and pair compatibility are determining factors for the fitness of territorial animals. Although these aspects are often studied separately, for territorial monogamous species acquiring a territory and obtaining a mate are not mutually exclusive. In this study, we investigated territory acquisition and mate choice characteristics in a saturated population of the Eurasian beaver, Castor fiber , by comparing individuals that successfully acquired territories with ones that were available in the study area (potential competitors). We used body mass and familiarity with an area as proxies for competitive ability, and genetic measures of inbreeding and relatedness, as well as age difference between pair members as proxies for mate compatibility. Comparatively older individuals and ones familiar with an area had a higher probability of territory acquisition, indicating that competitive ability was important for territory acquisition, whereas mate compatibility characteristics generally were not. However, in pairs that had a large age difference (between pair members), annual reproductive success decreased in more inbred pairs. These findings indicate that there might be a trade-off between territory acquisition and pair compatibility in saturated populations, that is, individuals accept being paired with a suboptimal mate when acquiring a territory, owing to intense competition. Our study emphasizes the importance of incorporating both factors related to competitive ability and mate compatibility when investigating territory acquisition in animals. • Territory acquisition and mate choice are often linked in monogamous species. • Competitive ability affects territory acquisition in beavers. • Individuals accept being paired with a suboptimal mate when acquiring a territory. • There might be a trade-off between territory acquisition and pair compatibility. [ABSTRACT FROM AUTHOR]

Evolutionary and behavioural ecologists have long been interested in factors shaping the variation in mating behaviour observed in nature. Although much of the research on this topic has focused on the consequences of mate choice and mate change on annual reproductive success, studies of a potential positive link between mate fidelity and adult demographic rates have been comparatively rare. This is particularly true for long‐lived birds with multi‐year, socially monogamous pair bonds.We used a 26‐year capture–mark–recapture dataset of 3,330 black brent Branta bernicla nigricans to test whether breeding with a familiar mate improved future breeding propensity and survival. We predicted that experienced breeders nesting with a new partner would have rates of survival similar to familiar pairs because long‐lived species avoid jeopardizing survival since their lifetime fitness is sensitive to this vital rate. In contrast, we expected that any costs of breeding with a new partner would be paid through skipping the subsequent breeding attempt.We found that unfamiliar pairs had lower subsequent breeding propensity than faithful partners. However, contrary to our expectations, individuals breeding with a new mate also suffered reduced survival.These results add to a small number of studies indicating that a positive relationship between mate retention and adult demographic rates may exist in a diverse array of avian species. Given these results, researchers should consider costs of mate change that extend beyond within‐season reproductive success to fully understand the potential adaptive basis for perennial social monogamy. We caution that if mate retention enhances survival prospects, improvements in annual reproductive success with pair‐bond length could be a secondary factor favouring perennial social monogamy, particularly in species with slower life‐history strategies. Furthermore, some cases where annual reproductive success does not improve with pair‐bond duration, yet multi‐year pair bonds are common, could be explained by benefits afforded by mate fidelity to adult vital rates. [ABSTRACT FROM AUTHOR]

For many species, there is evidence that breeding performance changes as an individual ages. In iteroparous species, breeding performance often increases through early life and is expected to level out or even decline (senesce) later in life. An individual's sex and conditions experienced in early life may also affect breeding performance and how this changes with age.Long‐term monitoring of individuals from reintroduced populations can provide unique opportunities to explore age‐related trends in breeding performance that might otherwise be logistically challenging.We used a unique dataset from a reintroduced population of white‐tailed eagles Haliaeetus albicilla in Scotland, which has been intensively monitored since their initial reintroduction in 1975, to study age‐ and sex‐specific trends in two measures of breeding performance. This monitoring provided data on the breeding performance of known individuals ranging in age from 3 to 26 years. We also explored changes in breeding performance in relation to early life experience (i.e., whether they were released or fledged in the wild).Breeding performance increased with age in early life in a similar manner for both sexes. We found stronger evidence for senescence in breeding performance in males than females. However, late‐life female breeding success was associated with early life experience, while male senescent trends were not apparently impacted by conditions experienced during early life.Sexual differences in senescence mean that older males are less likely to breed successfully compared to older females, and this may influence females' mate changes later in life. This difference may suggest a linked sexual difference in survival rates or the possibility of proactive partner change by females in later life in this typically monogamous biparental species. This article uses a unique individual‐based long‐term dataset derived from the reintroduction of white‐tailed eagles in Scotland to examine sex‐specific trends in reproductive senescence. Male white‐tailed eagles age faster than females, possible evidence for toy‐boy relationships in later life. [ABSTRACT FROM AUTHOR]

Individuals in species with long-term social monogamy often incur fitness costs after mate change. We evaluated the relative contributions of mate familiarity and male breeding experience to the costs of mate change of female black brant geese (Branta bernicla nigricans). We assessed the effects of mate change on relative nest initiation date, clutch size, brood size at hatch, growth rates of goslings, and prefledging survival of offspring. We modeled variation in relative nest initiation dates, clutch size, initial brood size, and gosling growth rates using generalized linear mixed models in Program R. We estimated prefledging survival with Cormack-Jolly-Seber models in Program MARK using reencounters of webtagged goslings. Mate change had a small effect on relative nest initiation date, clutch size, and initial brood size, but no effect on growth rates of brant goslings. Females breeding with an unfamiliar, but experienced male had goslings with higher prefledging survival rates (ϕ= 0.44 ± 0.11 [95% confidence interval]) than those breeding with a familiar, experienced mate (ϕ= 0.30 ± 0.04). However, females that changed mates and re-paired with an inexperienced male had goslings with substantially lower prefledging survival rates (ϕ= 0.20 ± 0.04) than any other group of females. Our findings indicate that reproductive output by female brant is affected by male experience rather than mate familiarity. We believe that female brant typically benefit from mate retention because most will not acquire an experienced partner after mate change. [ABSTRACT FROM AUTHOR]

In birds, changing mates generally results in decreased breeding success. Although costs and benefits of pair break-up have been well studied, endocrine mechanisms associated with mate change are poorly known. We measured baseline and stress- induced corticosterone levels in relation to mate change in Black-legged Kittiwakes (Rissa tridactyla). Baseline corticosterone levels were higher in kittiwakes breeding with a new mate than in kittiwakes that did not change mate. Stress-induced corticosterone levels were not influenced by change of mate. Elevated baseline corticosterone levels in birds breeding with a new mate could result from the social stress associated with pair break-up or mirror a higher energetic demand resulting from a lack of coordination between new pair members. Our results emphasize the usefulness of corticosterone levels in elucidating the effects of mate change on the energetic demands of reproduction in free-living birds. [ABSTRACT FROM AUTHOR]