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

Abstract

The Humboldt Current System is the most productive upwelling system globally in terms of fish and sustains huge populations of guano-producing birds as well as the world's largest single-species fishery targeting the Peruvian anchovy Engraulis ringens. Peruvian boobies Sula variegata and Guanay cormorants Phalacrocorax bougainvillii are the most abundant seabird species in the system and feed mainly on anchovies. By using high precision GPS and time−depth recorders, we compared the horizontal and vertical movements of the 2 species to examine whether segregation occurs between their foraging areas and whether there is any evidence for prey depletion close to large colonies. A simultaneous acoustic cruise in the foraging area of the 2 bird species estimated the vertical and horizontal distributions of anchovy schools. During the study period in austral spring 2008, the 2 bird species foraged in the same area, at relatively short distance from the colony (average, 19 to 20 km). Both species foraged at similar times of the day, although Peruvian boobies tended to leave earlier in the morning and return later in the evening than did the cormorants. Foraging trips were similar in duration, distance covered and range. Peruvian anchovies were abundant and schools occurred at shallow depths (median, 7 m; range, 3 to 34 m), mainly to the north and west of the colony where foraging bouts of the 2 species overlapped extensively. Cormorants are mainly pelagic surface divers, diving at shallow depths (median, 4 m) but reaching up to 32 m depth, and are thus able to track all the depths at which anchovies occurred during the study period. Peruvian boobies are plunge divers able to reach occasionally 10 m (median, 2 m), and are thus able to reach only shallow anchovy schools. No sexspecific differences in horizontal or vertical movements occurred between males and females in the 2 species. We suggest that the absence of significant differences between horizontal movements of boobies and cormorants, the relative short duration of their trips and the high number of chicks fledged were probably explained by the high abundance and accessibility of anchovies. Differences may be exacerbated during years of low anchovy abundance or accessibility, especially El Niño years. KEY WORDS: Peruvian anchovy · Telemetry · Phalacrocorax bougainvillii · Sula variegataResale or republication not permitted without written consent of the publisher

Predictive modelling of habitat selection by marine predators with respect to the abundance and depth distribution of pelagic prey

“…This is consistent with observed mean maximum dive depths of 1·8 m ± 1·4 m for Peruvian Boobies (n = 593) and 6·3 m ± 4·9 m for Guanay Cormorants (n = 2492) (Weimerskirch et al . ). The predicted probability of diving increased steeply at shallow depths for Peruvian Boobies, and more slowly for Guanay Cormorants (Fig.…”

“…Diving locations were identified using a combination of global positioning system (GPS) and time‐depth recorder (TDR) data (see Weimerskirch et al . ). The prey field was represented by Bayesian posterior predictions of the three‐dimensional spatial distribution of prey based on contemporaneous acoustic survey data (Boyd et al .…”

“…; Weimerskirch et al . ). Gaps in the GPS data were geo‐referenced by interpolating between locations immediately before and after the gap.…”

The Evolution of Seabirds in the Humboldt Current: New Clues from the Pliocene of Central Chile

“…The small Neogene cormorant Phalacrocorax sp., a possible ecological analogue of the Red-legged Cormorant P. gaimardi , is by far the most common cormorant until the Late Pliocene, whereas specimens identifiable as the Guanay cormorant P. bougainvillii are scarce. In contrast, the Guanay cormorant is currently one of the most abundant and main guano-producing species in the PCP [56], and it is also the most abundant species in Pleistocene sites of southern Peru [57]. This change in dominance is most likely related to the warmer oceanic conditions during the Pliocene [58], and their effect on the main prey of the Guanay: the Peruvian anchovy.…”

Effects of variation in the abundance and distribution of prey on the foraging success of central place foragers

“…However, the pursuit‐diving Guanay Cormorant is capable of reaching greater depths than the plunge‐diving Peruvian Booby (Weimerskirch et al . ). There is also some evidence that Guanay Cormorants may require denser prey schools for successful prey capture than Peruvian Boobies (Nelson ).…”