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Marine Biology 149: 139-148 (2006)
Foraging strategies and prey encounter rate of free-ranging little penguins.
Ropert-Coudert, Y., Kato, A, Wilson, R. P. and Cannell, B.
There is little information on the effort put into
foraging by seabirds, even though it is fundamental to
many issues in behavioural ecology. Recent researchers
have used changes in the underwater cruising speed of
penguins to allude to prey ingestion since accelerations
are thought to reflect the encounter and pursuit of prey.
In this study, we attached minute accelerometers, to
determine flipper beat frequency as a proxy for prey
pursuit, to Little Penguins Eudyptula minor foraging in
shallow waters in Western Australia. During diving,
Little Penguins flapped continuously and at a regular
pace of 3.16 Hz while descending the water column and
throughout the bottom phase of most dives. However,
the frequency and amplitude of wingbeats increased
transitorily, reaching 3.55.5 Hz, during some dives
indicating prey pursuit. Pursuit phases lasted a mean of
2.9}3.3 s and occurred principally during the bottom
phases of dives (75.4%). Most dives in all birds (86%)
had a clear square-shaped depth profile indicating
feeding activity near the seabed in the shallow waters of
the bays. Hourly maximum depth, time spent underwater,
percentage of dives with pursuit events and catch
per unit effort showed an overall increase from zero at
ca. 0500 h to a maximum during the hours around midday
before decreasing to zero by 1900 h. During pursuit
phases, Little Penguins headed predominantly downward,
probably using the seabed to assist them in trapping
their prey. In the light of our results, we discuss
depth use by Little Penguins and their allocation of
foraging effort and prey capture success as a function of
environmental conditions.
PG06-01
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