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Patterns of GPS tracks suggest nocturnal foraging by incubating Peruvian pelicans (Pelecanus thagus).

Zavalaga CB, Dell'Omo G, Becciu P, Yoda K - PLoS ONE (2011)

Bottom Line: The nocturnal foraging strategy of Peruvian pelicans may reduce food competition with the sympatric and strictly diurnal Guanay cormorants (Phalacrocorax bougainvillii), Peruvian boobies (Sula variegata) and Blue-footed boobies (S. nebouxii), which were present on the island in large numbers.Likewise, plankton bioluminescence might be used by pelicans as indirect cues to locate anchovies during their upward migration at night.The foraging success of pelicans at night may be enhanced by seizing prey close to the sea surface using a sit-and-wait strategy.

View Article: PubMed Central - PubMed

Affiliation: Graduate School of Environmental Studies, Nagoya University, Nagoya, Japan. cbz3724@alum.uncw.edu

ABSTRACT
Most seabirds are diurnal foragers, but some species may also feed at night. In Peruvian pelicans (Pelecanus thagus), the evidence for nocturnal foraging is sparse and anecdotal. We used GPS-dataloggers on five incubating Peruvian pelicans from Isla Lobos de Tierra, Perú, to examine their nocturnality, foraging movements and activities patterns at sea. All instrumented pelicans undertook nocturnal trips during a 5-7 day tracking period. Eighty-seven percent of these trips (n = 13) were strictly nocturnal, whereas the remaining occurred during the day and night. Most birds departed from the island after sunset and returned a few hours after sunrise. Birds traveled south of the island for single-day trips at a maximum range of 82.8 km. Overall, 22% of the tracking period was spent at sea, whereas the remaining time was spent on the island. In the intermediate section of the trip (between inbound and outbound commutes), birds spent 77% of the trip time in floating bouts interspersed by short flying bouts, the former being on average three times longer than the latter. Taken together, the high sinuosity of the bird's tracks during floating bouts, the exclusively nocturnal trips of most individuals, and the fact that all birds returned to the island within a few hours after sunrise suggest that pelicans were actively feeding at night. The nocturnal foraging strategy of Peruvian pelicans may reduce food competition with the sympatric and strictly diurnal Guanay cormorants (Phalacrocorax bougainvillii), Peruvian boobies (Sula variegata) and Blue-footed boobies (S. nebouxii), which were present on the island in large numbers. Likewise, plankton bioluminescence might be used by pelicans as indirect cues to locate anchovies during their upward migration at night. The foraging success of pelicans at night may be enhanced by seizing prey close to the sea surface using a sit-and-wait strategy.

Show MeSH
Sinuosity index during the beginning (outbound path), middle (food search) and ending (inbound path) stages of the trip.Box plots depict the 10, 25, 50, 75 and 90 percentiles of the distribution. A sinuosity index close to one means high path linearity.
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pone-0019966-g003: Sinuosity index during the beginning (outbound path), middle (food search) and ending (inbound path) stages of the trip.Box plots depict the 10, 25, 50, 75 and 90 percentiles of the distribution. A sinuosity index close to one means high path linearity.

Mentions: The sinuosity index of the tracks during floating bouts was significantly higher than those during inbound and outbound flights, and during flying bouts that connected two consecutive landings on the water (REML, F3,12 = 16.4, P = 0.0002, Ryan's Q-test for pairwise comparisons, Fig. 3). Thus, these periods on the water surface were probably related to foraging. When the two trips with records during day/night hours were partitioned into two sections, we found that the proportion of the total floating time was higher at night (95% of the time from nautical sunset twilight to arrival on the island) than during the day (65% of the time from island departure to nautical sunset twilight). Likewise, the sinuosity index was higher (t-test, t = 4.6, P<0.0001) and the duration of floating bouts longer (t-test, t = 2.45, P  = 0.015) during nighttime.


Patterns of GPS tracks suggest nocturnal foraging by incubating Peruvian pelicans (Pelecanus thagus).

Zavalaga CB, Dell'Omo G, Becciu P, Yoda K - PLoS ONE (2011)

Sinuosity index during the beginning (outbound path), middle (food search) and ending (inbound path) stages of the trip.Box plots depict the 10, 25, 50, 75 and 90 percentiles of the distribution. A sinuosity index close to one means high path linearity.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC3102073&req=5

pone-0019966-g003: Sinuosity index during the beginning (outbound path), middle (food search) and ending (inbound path) stages of the trip.Box plots depict the 10, 25, 50, 75 and 90 percentiles of the distribution. A sinuosity index close to one means high path linearity.
Mentions: The sinuosity index of the tracks during floating bouts was significantly higher than those during inbound and outbound flights, and during flying bouts that connected two consecutive landings on the water (REML, F3,12 = 16.4, P = 0.0002, Ryan's Q-test for pairwise comparisons, Fig. 3). Thus, these periods on the water surface were probably related to foraging. When the two trips with records during day/night hours were partitioned into two sections, we found that the proportion of the total floating time was higher at night (95% of the time from nautical sunset twilight to arrival on the island) than during the day (65% of the time from island departure to nautical sunset twilight). Likewise, the sinuosity index was higher (t-test, t = 4.6, P<0.0001) and the duration of floating bouts longer (t-test, t = 2.45, P  = 0.015) during nighttime.

Bottom Line: The nocturnal foraging strategy of Peruvian pelicans may reduce food competition with the sympatric and strictly diurnal Guanay cormorants (Phalacrocorax bougainvillii), Peruvian boobies (Sula variegata) and Blue-footed boobies (S. nebouxii), which were present on the island in large numbers.Likewise, plankton bioluminescence might be used by pelicans as indirect cues to locate anchovies during their upward migration at night.The foraging success of pelicans at night may be enhanced by seizing prey close to the sea surface using a sit-and-wait strategy.

View Article: PubMed Central - PubMed

Affiliation: Graduate School of Environmental Studies, Nagoya University, Nagoya, Japan. cbz3724@alum.uncw.edu

ABSTRACT
Most seabirds are diurnal foragers, but some species may also feed at night. In Peruvian pelicans (Pelecanus thagus), the evidence for nocturnal foraging is sparse and anecdotal. We used GPS-dataloggers on five incubating Peruvian pelicans from Isla Lobos de Tierra, Perú, to examine their nocturnality, foraging movements and activities patterns at sea. All instrumented pelicans undertook nocturnal trips during a 5-7 day tracking period. Eighty-seven percent of these trips (n = 13) were strictly nocturnal, whereas the remaining occurred during the day and night. Most birds departed from the island after sunset and returned a few hours after sunrise. Birds traveled south of the island for single-day trips at a maximum range of 82.8 km. Overall, 22% of the tracking period was spent at sea, whereas the remaining time was spent on the island. In the intermediate section of the trip (between inbound and outbound commutes), birds spent 77% of the trip time in floating bouts interspersed by short flying bouts, the former being on average three times longer than the latter. Taken together, the high sinuosity of the bird's tracks during floating bouts, the exclusively nocturnal trips of most individuals, and the fact that all birds returned to the island within a few hours after sunrise suggest that pelicans were actively feeding at night. The nocturnal foraging strategy of Peruvian pelicans may reduce food competition with the sympatric and strictly diurnal Guanay cormorants (Phalacrocorax bougainvillii), Peruvian boobies (Sula variegata) and Blue-footed boobies (S. nebouxii), which were present on the island in large numbers. Likewise, plankton bioluminescence might be used by pelicans as indirect cues to locate anchovies during their upward migration at night. The foraging success of pelicans at night may be enhanced by seizing prey close to the sea surface using a sit-and-wait strategy.

Show MeSH