Reproduction in birds is known to involve several costly processes which make breeding a
demanding period in terms of energy and time investment. Among the several breeding
attempts, first reproduction is especially crucial because recruits lack the experience than older
breeders have or there is a higher proportion of low-quality individuals. In some species, one
sex invests more in parental care than the other, leading to sex-biased mortalities or reduced
future breeding propensity. In the current study, we use multievent mark-recapture models to
estimate transience probabilities as a proxy to assess the survival costs of first reproduction in
two species of Procellariiformes seabirds: Scopoli’s shearwater and European Storm petrel.
Results show, for Scopoli’s shearwaters, that newly marked females have higher probabilities to
die as a cost of first reproduction (0,119; 95% CI: 0,075 – 0,184) than males (0,035; 95% CI:
0,0065 – 0,16). This result suggests that females are paying higher survival costs of reproduction
than males due to egg production. The costs this implies for females seem to have an importance
driving population dynamics and is likely additive to the impact of bycatch mortality. Finally,
results for European Storm petrel are not conclusive given that some models show lack of
power.
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