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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.

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Frequency distribution of ground speed between consecutive GPS locations of incubating Peruvian pelicans.The inset graph shows the cut-off value to discriminate flying speeds from floating on the water speeds. The outer distribution depicts the mean flight speed.
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pone-0019966-g001: Frequency distribution of ground speed between consecutive GPS locations of incubating Peruvian pelicans.The inset graph shows the cut-off value to discriminate flying speeds from floating on the water speeds. The outer distribution depicts the mean flight speed.

Mentions: The spatial data from loggers were mapped and analyzed using ArcGIS 9.2 Geographic Information System (ESRI Inc., Redlands, CA). The positions were projected on the UTM coordinate system (Zone 14S) for all spatial analysis. The high resolution (<10 m in >95% of locations after excluding fixes with DOP values >6, GiPSy-2 user's manual, www.technosmart.eu) and short recording intervals of the loggers allowed us to identify the precise time budget of pelicans at sea. GPS data showed that after a nest shift, pelicans spent a variable amount of time on different activities away from the nest before departing for a trip. Likewise, some birds did not return to the nest immediately after completing a trip (see results), and consequently, for more accurate estimates, we defined a trip as the time elapsed between the departure from and arrival to the island. Instantaneous flight speeds were calculated from the distance and time between two consecutive GPS locations after excluding all points on land. An inspection of the frequency distribution of speeds revealed a discontinuity in movement patterns associated with speeds >6 km•h−1 (Fig. 1). We used this value to calculate the proportion of time within a trip when the bird was floating on the water (<6 km•h−1) and consequently, the proportion of time spent flying (> 6 km•h−1). This cut-off value has been reported as a typical pelican surface drifting speed [8]. Trips were divided in three sections:


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)

Frequency distribution of ground speed between consecutive GPS locations of incubating Peruvian pelicans.The inset graph shows the cut-off value to discriminate flying speeds from floating on the water speeds. The outer distribution depicts the mean flight speed.
© Copyright Policy
Related In: Results  -  Collection

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

pone-0019966-g001: Frequency distribution of ground speed between consecutive GPS locations of incubating Peruvian pelicans.The inset graph shows the cut-off value to discriminate flying speeds from floating on the water speeds. The outer distribution depicts the mean flight speed.
Mentions: The spatial data from loggers were mapped and analyzed using ArcGIS 9.2 Geographic Information System (ESRI Inc., Redlands, CA). The positions were projected on the UTM coordinate system (Zone 14S) for all spatial analysis. The high resolution (<10 m in >95% of locations after excluding fixes with DOP values >6, GiPSy-2 user's manual, www.technosmart.eu) and short recording intervals of the loggers allowed us to identify the precise time budget of pelicans at sea. GPS data showed that after a nest shift, pelicans spent a variable amount of time on different activities away from the nest before departing for a trip. Likewise, some birds did not return to the nest immediately after completing a trip (see results), and consequently, for more accurate estimates, we defined a trip as the time elapsed between the departure from and arrival to the island. Instantaneous flight speeds were calculated from the distance and time between two consecutive GPS locations after excluding all points on land. An inspection of the frequency distribution of speeds revealed a discontinuity in movement patterns associated with speeds >6 km•h−1 (Fig. 1). We used this value to calculate the proportion of time within a trip when the bird was floating on the water (<6 km•h−1) and consequently, the proportion of time spent flying (> 6 km•h−1). This cut-off value has been reported as a typical pelican surface drifting speed [8]. Trips were divided in three sections:

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