title: Seasonality in marine ecosystems: Peruvian seabirds, anchovy, and oceanographic conditions.
abstract: In fluctuating environments, matching breeding timing to periods of high resource availability is crucial for the fitness of many vertebrate species, and may have major consequences on population health. Yet, our understanding of the proximate environmental cues driving seasonal breeding is limited. This is particularly the case in marine ecosystems, where key environmental factors and prey abundance and availability are seldom quantified. The Northern Humboldt Current System (NHCS) is a highly productive, low-latitude ecosystem of moderate seasonality. In this ecosystem, three tropical seabird species (the Guanay Cormorant Phalacrocorax bougainvillii, the Peruvian Booby Sula variegata, and the Peruvian Pelican Pelecanus thagus) live in sympatry and prey almost exclusively on anchovy, Engraulis ringens. From January 2003 to December 2012, we monitored 31 breeding sites along the Peruvian coast to investigate the breeding cycle of these species. We tested for relationships between breeding timing, oceanographic conditions, and prey availability using occupancy models. We found that all three seabird species exhibited seasonal breeding patterns, with marked interspecific differences. Whereas breeding mainly started during the austral winter/early spring and ended in summer/early fall, this pattern was stronger in boobies and pelicans than in cormorants. Breeding onset mainly occurred when upwelling was intense but ecosystem productivity was below its annual maxima, and when anchovy were less available and in poor physiological condition. Conversely, the abundance and availability of anchovy improved during chick rearing and peaked around the time of fledging. These results suggest that breeding timing is adjusted so that fledging may occur under optimal environmental conditions, rather than being constrained by nutritional requirements during egg laying. Adjusting breeding time so that fledglings meet optimal conditions at independence is unique compared with other upwelling ecosystems and could be explained by the relatively high abundances of anchovy occurring throughout the year in the NHCS.
authors.forename: Giannina
authors.initials: G
authors.lastname: Passuni
authors.forename: Christophe
authors.initials: C
authors.lastname: Barbraud
authors.forename: Alexis
authors.initials: A
authors.lastname: Chaigneau
authors.forename: Hervé
authors.initials: H
authors.lastname: Demarcq
authors.forename: Jesus
authors.initials: J
authors.lastname: Ledesma
authors.forename: Arnaud
authors.initials: A
authors.lastname: Bertrand
authors.forename: Ramiro
authors.initials: R
authors.lastname: Castillo
authors.forename: Angel
authors.initials: A
authors.lastname: Perea
authors.forename: Julio
authors.initials: J
authors.lastname: Mori
authors.forename: Vincent A
authors.initials: VA
authors.lastname: Viblanc
authors.forename: Jose
authors.initials: J
authors.lastname: Torres-MaitaA
authors.forename: Sophie
authors.initials: S
authors.lastname: Bertrand
mesh_terms: D000818:Animals; D001717:Birds / Q000502:physiology*; D017753:Ecosystem; D005399:Fishes / Q000502:physiology*; D009792:Oceans and Seas; D010568:Peru; D011235:Predatory Behavior; D012098:Reproduction / Q000502:physiology; D012621:Seasons; D013997:Time Factors