At-sea movement patterns and diving behavior of Peruvian boobies Sula variegata in northern Peru

Abstract

GPS loggers and time-depth recorders were used to characterize the foraging behavior of the sexually dimorphic Peruvian booby Sula variegata on 2 islands in northern Peru. We evaluated whether (1) its foraging behavior differed from tropical boobies and temperate gannets (the Peruvian boobies feed in areas of enhanced productivity and high fish density), and (2) females and males exploited different foraging habitats as a consequence of size dimorphism. Birds foraged only during daylight hours, 1 to 3 times a day, in trips of short duration (median = 1.8 h). Overall, 92% of the total foraging time was spent flying. They fed exclusively on anchovetas Engraulis ringens, which were captured in shallow dives (median = 2.5 m, max = 8.8 m) with a dive median rate of 11 dives h -1 (max = 37 dives h -1 ). The median foraging range was 25 km (max = 68 km), whereas the median total distance traveled was 69 km (max = 179 km). Foraging site fidelity was high, and the orientation of foraging flights in any given day was similar among birds that departed at the same time. There were no sex-specific differences in 13 of 15 foraging variables; however, females dived slightly deeper and spent a larger proportion of time sitting on the water. We speculate that (1) the foraging behavior of Peruvian boobies contrasts with that of their tropical and temperate relatives as a result of the proximity and predictability of food sources, elevated energetic demands of the brood (up to 4 chicks) and high prey encounter rate in the Peruvian upwelling system, and (2) the lack of spatial segregation between sexes may be related to the attraction of birds to feeding aggregations that are formed in the vicinity of the colonies. Once the foraging patches are localized, females dive deeper because of passive mechanisms associated with a heavier mass.

A new algorithm for the identification of dives reveals the foraging ecology of a shallow-diving seabird using accelerometer data

“…Our results are in accordance with those of other studies which investigated sex difference in foraging activity (Phalan et al 2007;Zavalaga et al 2010) and trip length (Ramos et al 2009). Nevertheless, males dived more frequently than females during nighttime.…”

Foraging in Guanay cormorant and Peruvian booby, the major guano-producing seabirds in the Humboldt Current System

“…We found little sex-specific differences in foraging characteristics in Peruvian boobies, as did Zavalaga et al (2010b); however, they displayed a significant difference in size, females being 16% heavier and 5% larger than males (Table 1). Boobies are well known to display a reversed sexual dimorphism (Nelson 1978), and several studies have found sex differences in foraging behaviour in several species (Lewis et al 2005, Zavalaga et al 2007, Weimerskirch et al 2009a and have suggested that they are related to the extent that sexual dimorphism exists for some foraging features, such as dive depths or foraging duration, or to different roles in parental investment.…”

Variability of resource partitioning in sympatric tropical boobies

“…Masked and red-footed boobies at Tromelin Island demonstrated a low degree of fidelity in successive foraging trips, a strategy that likely reflects the dynamic, unpredictable nature of prey patches associated with sub-surface marine predators (Weimerskirch 2007). High fidelity to foraging sites has been demonstrated in Peruvian boobies (Sula variegata; Zavalaga et al 2010) and other marine predators (Baduini et al 2006, Baylis et al 2008, Call et al 2008, Pettex et al 2010. However, these studies were all conducted in high productivity environments.…”