Abstract
The El Niño Southern Oscillation (ENSO) is a recurrent climatic pattern with important ecological consequences for seabirds due to its impacts on the abundance and distribution of food resources. We investigated the effects of ENSO phases on the foraging ecology of a marine top predator at Clarion Island in the Eastern Tropical Pacific using GPS and time-depth recorder data and regurgitates from incubating masked boobies (Sula dactylatra) during 3 consecutive years. Foraging locations were recorded in 2016 (El Niño, one female, three males), 2017 (neutral; six females, nine males), and 2018 (La Niña; eight females, ten males). Local sea surface temperature (SST) and chlorophyll-a concentration (CHL) within the birds’ foraging range were compared among the 3 years. Regurgitates were collected opportunistically from 25 and 31 incubating adults in 2017 and 2018, respectively. Average local CHL and SST were similar among years (mean SST 25 °C; mean CHL 0.10 and of 0.09 mg m−3 in January and March, respectively). Masked boobies travelled a maximum of 66 ± 34 km from the colony. The maximum trip duration was 7.7 ± 3.4 h and total distance travelled during a foraging trip was 164 ± 73 km, with no sex- or year-related differences. Masked boobies mainly caught flying fish, but their diet also included one squid and six other fish families. In contrast to previously reported changes in foraging ecology of seabirds, masked boobies at Clarion Island seemed to be unaffected during El Niño, because the local oceanography was relatively unperturbed by ENSO oscillations.
Highlights
The El Niño-Southern Oscillation (ENSO) is a dominant driver of inter-annual variabilities in the physical and biogeochemical states in the Pacific
There were no significant differences in foraging trip parameters among birds in relation to incubation status, sex, or the three tracking periods (January 2016, March 2017, and March 2018) (Fig. 5) and there were no significant interactions between the factors (Table 1)
Despite the limited number of samples, this study provides novel evidence for the foraging ecology of masked boobies at Clarion Island during consecutive years
Summary
The El Niño-Southern Oscillation (ENSO) is a dominant driver of inter-annual variabilities in the physical and biogeochemical states in the Pacific. Seabirds may respond to changes in the availability of their main prey by switching the targeted prey species (Ancona et al 2012) and adjusting their foraging behavior (Harding et al 2007; Elliott et al 2008; Castillo-Guerrero et al 2016). Masked boobies (Sula dactylatra) represent an ideal species for documenting the effects of El Niño events in a tropical marine predator. This species is large enough to carry tracking devices, continues breeding even during El Niño events (Nelson 1978), and individuals may adjust their foraging movements and prey items according to availability (Nelson 1978; Sommerfeld et al 2015)
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