Birth dates vary with fixed and dynamic maternal features, offspring sex, and extreme climatic events in a high‐latitude marine mammal

Abstract

Reproductive synchrony tends to be widespread in diverse species of plants and animals, especially at higher latitudes. However, for long‐lived mammals, birth dates for different individuals can vary by weeks within a population. A mother's birth timing can reveal useful information about her reproductive abilities and have important implications for the characteristics and survival of her offspring. Despite this, our current knowledge of factors associated with variation in birth dates is modest. We used long‐term data for known‐age Weddell seals in Antarctica and a Bayesian hierarchical modeling approach to study how birth dates varied with fixed and temporally varying features of mothers, whether sex allocation varied with birth timing, and annual variation in birth dates. Based on birth dates for 4465 pups born to 1117 mothers aged 4–31, we found that diverse features of mothers were associated with variation in birth dates. Maternal identity was the most important among these. Unlike most studies, which have reported that birth dates occur earlier as mothers age, we found that birth dates progressively occurred earlier in the year in the early part of a mother's reproductive life, reached a minimum at age 16, and then occurred later at later ages. Birth dates were positively related to a mother's age at primiparity and recent reproductive effort. The earliest birth dates were for pups born to prime‐age mothers who did not reproduce in the previous year but began reproduction early in life, suggesting that females in the best condition gave birth earlier than others. If so, our finding that male pups tended to be born earlier than females provides support for the Trivers–Willard sex‐allocation model. Average birth dates were quite consistent across years, except for 2 years that had notable delays and occurred during the period when massive icebergs were present and disrupted the ecosystem.

Engaging ‘the crowd’ in remote sensing to learn about habitat affinity of the Weddell seal in Antarctica

“…; Rotella et al. ). Weddell seals are probably the best studied of all pinnipeds, at least regarding its natural history and demography.…”

“…The southernmost breeding population of mammals in the world is the Weddell seal (Leptonychotes weddellii) in McMurdo Sound, Ross Sea, a population involved in continuous mark-resight studies since the late 1960s (Stirling 1969;Siniff et al 1977;Testa and Siniff 1987;Cameron and Siniff 2004;Garrott et al 2012;Rotella et al 2016). Weddell seals are probably the best studied of all pinnipeds, at least regarding its natural history and demography.…”

“…Traditional methods for assessing populations of Weddell seals have included aerial surveys (Bester et al 2002;Bengtson et al 2011); ship-board surveys employing distance sampling (i.e. the Antarctic Pack-ice Seals [APIS] surveys as in Bengtson et al 2011), other ship-board surveys (Ackley et al 2003;Flores et al 2008;Southwell et al 2004) and ground-or ice-based surveys during the austral spring (Stirling 1969;Siniff et al 1977;Testa and Siniff 1987;Cameron and Siniff 2004;Garrott et al 2012;Rotella et al 2016). Erickson et al (1971), Seal et al (1971) and then Erickson and Hanson (1990), provided a review of Antarctic seals, revealing that~6100 km 2 of sea ice had been searched across six studies during ; subsequent studies were added in 1996-2000 (Southwell et al 2012).…”

Maternal and offspring effects on the timing of parturition in western Steller sea lions (Eumetopias jubatus)

“…Much contemporary research on birth timing has tested for effects of these factors with implications that climate conditions, food availability, status, disease or contaminant loads directly or indirectly affect maternal body condition (e.g., Gilmartin et al 1976;Skogland 1984;Rachlow and Bowyer 1991;Lunn and Boyd 1993;Bowen et al 2003). Additionally, climate conditions and food availability can influence the growth of a developing fetus and whether or not the mother skips a year of giving birth, which in turn, have been correlated with subsequent parturition date (Drickamer 1974; Rotella et al 2016).…”

A re-examination of the timing of pupping for Steller sea lions Eumetopias jubatus breeding on two islands in Alaska

“…Intrinsic factors that play a role can include age, body size, and previous reproductive history (e.g. Lunn et al 1994, Plard et al 2014, Rotella et al 2016. For example, Plard et al (2014) showed that parturition date in roe deer was negatively related to adult quality (measured as median body mass) and age.…”