Elucidating the full eco‐evolutionary consequences of climate change requires quantifying the impact of extreme climatic events (ECEs) on selective landscapes of key phenotypic traits that mediate responses to changing environments. Episodes of strong ECE‐induced selection could directly alter population composition, and potentially drive micro‐evolution. However, to date, few studies have quantified ECE‐induced selection on key traits, meaning that immediate and longer‐term eco‐evolutionary implications cannot yet be considered. One widely expressed trait that allows individuals to respond to changing seasonal environments, and directly shapes spatio‐seasonal population dynamics, is seasonal migration versus residence. Many populations show considerable among‐individual phenotypic variation, resulting in ‘partial migration’. However, variation in the magnitude of direct survival selection on migration versus residence has not been rigorously quantified, and empirical evidence of whether seasonal ECEs induce, intensify, weaken or reverse such selection is lacking. We designed full annual cycle multi‐state capture–recapture models that allow estimation of seasonal survival probabilities of migrants and residents from spatio‐temporally heterogeneous individual resightings. We fitted these models to 9 years of geographically extensive year‐round resighting data from partially migratory European shags Phalacrocorax aristotelis. We thereby quantified seasonal and annual survival selection on migration versus residence across benign and historically extreme non‐breeding season (winter) conditions, and tested whether selection differed between females and males. We show that two of four observed ECEs, defined as severe winter storms causing overall low survival, were associated with very strong seasonal survival selection against residence. These episodes dwarfed the weak selection or neutrality evident otherwise, and hence caused selection through overall annual survival. The ECE that caused highest overall mortality and strongest selection also caused sex‐biased mortality, but there was little overall evidence of sex‐biased selection on migration versus residence. Our results imply that seasonal ECEs and associated mortality can substantially shape the landscape of survival selection on migration versus residence. Such ECE‐induced phenotypic selection will directly alter migrant and resident frequencies, and thereby alter immediate spatio‐seasonal population dynamics. Given underlying additive genetic variation, such ECEs could potentially cause micro‐evolutionary changes in seasonal migration, and thereby cause complex eco‐evolutionary population responses to changing seasonal environments.

Some opportunistic vertebrates exploit, and may largely rely upon, food generated by human activities. Better understanding the influence of this additional anthropogenic food on species' ecology would inform sustainable waste management. In the Balearic Archipelago of Spain, closure of an open‐air landfill site provided an experimental setting to measure the effect of removing anthropogenic food on the average body mass, breeding parameters and body condition of opportunistic Yellow‐legged Gulls Larus michahellis. After landfill closure there was a significant decline in the average body mass of breeding females and males (−10.4 and −7.8%, respectively), in average egg volume (−4.8%), and a shift in the modal clutch size from three to two eggs. Body condition decreased after landfill closure in both sexes. In breeding females, the drop in body weight was greater for birds with a low body size index. The differential response to a reduction of anthropogenic food between small and large birds suggests that food of anthropogenic origin contributes to tempering the effects of natural selection, making the long‐term demographic effects of changes in food supply difficult to predict.

Conditions during early life, including maternal cohort effects, can influence the future fitness of individuals. This may be particularly true for longdistance migrating birds, because, apart from conditions experienced by cohorts during rearing, conditions during early life in regions far from breeding grounds may also influence their population dynamics. Very little is known about the fitness consequences of those conditions experienced by juveniles after independence, especially in wild populations and for longlived birds. We used multi-event capture-recapture-recovery models and a unique 26-year dataset for the Audouin's gull (Larus audouinii) to assess for the first time whether survival was influenced by early conditions, both during the rearing period (i.e. a maternal cohort effect potentially affected by density dependence) and the first winter (i.e. a cohort effect driven by climate when birds disperse to wintering grounds). Our results show that juvenile survival was highly sensitive to early-life conditions and that survival decreased with stronger density dependence and harsh climate. The two consecutive cohort effects were of similar magnitude and they may represent a selection filter. Thus, early-life conditions had a strong impact on survival, and neglecting this complexity may hinder our understanding on how populations of long-lived animals fluctuate and respond to perturbations.

Abstract. The control of overabundant vertebrates is often problematic. Much work has focused on population-level responses and overabundance due to anthropogenic subsidies. However, far less work has been directed at investigating responses following the removal of subsidies. We investigate the consequences of two consecutive perturbations, the closure of a landfill and an inadvertent poisoning event, on the trophic ecology (d 13 C, d 15 N, and d 34 S), survival, and population size of an overabundant generalist seabird species, the Yellow-legged Gull (Larus michahellis). We expected that the landfill closure would cause a strong dietary shift and the inadvertent poisoning a decrease in gull population size. As a long-lived species, we also anticipated adult survival to be buffered against the decrease in food availability but not against the inadvertent poisoning event. Stable isotope analysis confirmed the dietary shift towards marine resources after the disappearance of the landfill. Although the survival model was inconclusive, it did suggest that the perturbations had a negative effect on survival, which was followed by a recovery back to average values. Food limitation likely triggered dispersal to other populations, while poisoning may have increased mortality; these two processes were likely responsible for the large fall in population size that occurred after the two consecutive perturbations. Life-history theory suggests that perturbations may encourage species to halt existing breeding investment in order to ensure future survival. However, under strong perturbation pulses the resilience threshold might be surpassed and changes in population density can arise. Consecutive perturbations may effectively manage overabundant species.