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Diving and foraging in the Western Grebe
Ydenberg, R.C.; Forbes, L.S. (1988). Diving and foraging in the Western Grebe. Ornis Scandinavica 19: 129-133
In: Ornis Scandinavica. Munksgaard: Copenhagen. ISSN 0030-5693, more
Peer reviewed article  

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  • Ydenberg, R.C.
  • Forbes, L.S.

    We recorded the duration of successive dives, and pauses on the surface between dives, of foraging Western Grebes Aechmophorus occidentalis at Duck Lake, near Creston, British Columbia. Overall, the duration of a pause was positively related to the length of the preceding dive. Pauses shorter than expected (based on the length of the preceding dive) were defined to have a negative deviation from estimated surface time (DEVEST), while pauses longer than expected had positive DEVEST. The results show that the DEVEST in successive dive-pause cycles is highly positively correlated, so that the cumulative DEVEST first increases for a series of 10-100 dives, and then decreases over a long series. DEVEST has very little influence on dive duration. Western Grebes hunt fish schools, which are initially hard to find, but once found offer many captures. We hypothesize that the observed pattern of surface and underwater time results from a policy allowing western grebes to exploit fish schools more fully than if full recovery followed each dive.

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