In iteroparous species, intermittent breeding is an important life-history tactic that can greatly affect animal population growth and viability. Despite its importance, few studies have quantified the consequences of breeding pauses on lifetime reproductive output, principally because calculating lifetime reproductive output requires knowledge of each individual's entire reproductive history. This information is extremely difficult to obtain in wild populations. We applied novel statistical approaches that account for uncertainty in state assessment and individual heterogeneity to an 18-year capture-recapture dataset of 6,631 female southern elephant seals from Macquarie Island. We estimated survival and breeding probabilities, and investigated the consequences of intermittent breeding on lifetime reproductive output. We found consistent differences in females' demographic performance between two heterogeneity classes. In particular, breeding imbued a high cost on survival in the females from the heterogeneity class 2, assumed to be females of lower quality. Individual quality also appeared to play a major role in a female's decision to skip reproduction with females of poorer quality more likely to skip breeding events than females of higher quality. Skipping some breeding events allowed females from both heterogeneity classes to increase lifetime reproductive output over females that bred annually. However, females of lower quality produced less offspring over their lifetime. Intermittent breeding seems to be used by female southern elephant seals as a tactic to offset reproductive costs on survival and enhance lifetime reproductive output but remains unavoidable and driven by individual-specific constraints in some other females.

When to commence breeding is a crucial life-history decision that may be the most important determinant of an individual's lifetime reproductive output and can have major consequences on population dynamics. The age at which individuals first reproduce is an important factor influencing the intensity of potential costs (e.g. reduced survival) involved in the first breeding event. However, quantifying age-related variation in the cost of first reproduction in wild animals remains challenging because of the difficulty in reliably recording the first breeding event. Here, using a multi-event capture-recapture model that accounts for both imperfect detection and uncertainty in the breeding status on an 18-year dataset involving 6637 individuals, we estimated age and state-specific survival of female elephant seals (Mirounga leonina) in the declining Macquarie Island population. We detected a clear cost of first reproduction on survival. This cost was higher for both younger first-time breeders and older first-time breeders compared with females recruiting at age four, the overall mean age at first reproduction. Neither earlier primiparity nor delaying primiparity appear to confer any evolutionary advantage, rather the optimal strategy seems to be to start breeding at a single age, 4 years.

Studies of the mechanisms underlying climate‐induced population changes are critically needed to better understand and accurately predict population responses to climate change. Long‐lived migratory species might be particularly vulnerable to climate change as they are constrained by different climate conditions and energetic requirements during the breeding and non‐breeding seasons. Yet, most studies primarily focus on the breeding season of these species life cycle. Environmental conditions experienced in the non‐breeding season may have downstream effects on the other stages of the annual life cycle. Not investigating such effects may potentially lead to erroneous inferences about population dynamics. Combining demographic and tracking data collected between 2006 and 2013 at Kerguelen Island on a long‐lived migratory seabird, the Black‐Browed Albatross (Thalassarche melanophris), we investigated the links between sea surface temperature during the non‐breeding season and behavioural and phenological traits (at‐sea behaviour and migratory schedules) while accounting for different responses between birds of different sex and reproductive status (previously failed or successful breeders). We then explored whether variation in the foraging behaviour and timing of spring migration influenced subsequent reproductive performance. Our results showed that foraging activity and migratory schedules varied by both sex and reproductive status suggesting different energetic requirements and constraints among individuals. Higher sea surface temperatures during late winter, assumed to reflect poor winter conditions, were associated with an earlier departure from the wintering grounds and an extended pre‐breeding period. However, an earlier spring migration and an earlier return to Kerguelen grounds were associated with a lower breeding success. Our results highlighted that behaviour during some periods of the non‐breeding season, particularly towards the end of the wintering period and the pre‐breeding period, had a significant effect on the subsequent reproductive success. Therefore, caution needs to be given to all stages of the annual cycle when predicting the influence of climate on population dynamics. A http://onlinelibrary.wiley.com/doi/10.1111/1365-2435.13117/suppinfo is available for this article.

Recent studies unravelled the effect of climate changes on populations through their impact on functional traits and demographic rates in terrestrial and freshwater ecosystems, but such understanding in marine ecosystems remains incomplete. Here, we evaluate the impact of the combined effects of climate and functional traits on population dynamics of a long-lived migratory seabird breeding in the southern ocean: the black-browed albatross (Thalassarche melanophris, BBA). We address the following prospective question: "Of all the changes in the climate and functional traits, which would produce the biggest impact on the BBA population growth rate?" We develop a structured matrix population model that includes the effect of climate and functional traits on the complete BBA life cycle. A detailed sensitivity analysis is conducted to understand the main pathway by which climate and functional trait changes affect the population growth rate. The population growth rate of BBA is driven by the combined effects of climate over various seasons and multiple functional traits with carry-over effects across seasons on demographic processes. Changes in sea surface temperature (SST) during late winter cause the biggest changes in the population growth rate, through their effect on juvenile survival. Adults appeared to respond to changes in winter climate conditions by adapting their migratory schedule rather than by modifying their at-sea foraging activity. However, the sensitivity of the population growth rate to SST affecting BBA migratory schedule is small. BBA foraging activity during the pre-breeding period has the biggest impact on population growth rate among functional traits. Finally, changes in SST during the breeding season have little effect on the population growth rate. These results highlight the importance of early life histories and carry-over effects of climate and functional traits on demographic rates across multiple seasons in population response to climate change. Robust conclusions about the roles of various phases of the life cycle and functional traits in population response to climate change rely on an understanding of the relationships of traits to demographic rates across the complete life cycle.

In long-lived species, individuals can skip reproduction. The proportion of breeders affects population growth rate and viability, there is a need to investigate the factors influencing intermittent breeding. The theory predicts that if lack of experience is an important constraint, breeding probabilities should increase with experience for individuals of the same age, whereas under the so-called restraint hypothesis, breeding probabilities should increase with age regardless of experience. However, because the probability of detecting individuals in the wild is generally less than 1, it is difficult to know exactly the number of previous breeding episodes (breeding experience). To cope with this issue, we developed a hidden process model to incorporate experience as a latent state possibly influencing the probability of breeding. Using a 22-year mark-recapture dataset involving 9970 individuals, we analysed simultaneously experience and age effects on breeding probabilities in the kittiwake (Rissa tridactyla). We did not detect an influence of age on adult breeding probabilities. We found that inexperienced birds breed less frequently than experienced birds. Our approach enables us to highlight the key role of experience on adults breeding probabilities and can be used for a wide range of organisms for which detection is less than 1.