Co-operative underwater hunting behaviour observed in Loons (Gaviidae)

19 August 2010

Synchronized diving (presumably co-operative underwater hunting behaviour) observed in Loons (Gaviidae)

At about local sunset, a solitary loon (the bird) was observed on Miller Lake (HRM, NS, Canada). It was passively resting on the surface and was not diving. This period of relative inactivity was observed for about 15 minutes.

Then additional loons began to arrive (by air, LOL) from the east and north-east, calling, circling around the small island, and skidding onto the lake quite near the first loon (landing direction approximately south-east). Within a few minutes, there were exactly six (6) loons clustered in a close group not more than 10m extent.

After a few minutes, the loons (all six) began to dive (presumably for food) together. All six loons were underwater at the same time, for a period of roughly a minute or so at a time. They would then reemerge essentially at the same time (within about ten seconds), and then they would all rest on the surface for a minute or so. The beginning of each dive was especially closely synchronized, with all six birds diving underwater within a period of not more than 5 seconds (from first bird going underwater to the sixth bird going underwater). It was obvious that they were diving together.

This synchronized diving (and I presume cooperative underwater hunting for fish) continued for at least four or five cycles that we observed.

After a period of approximately ten minutes, the birds were no longer visible. Presumably they resurfaced behind the island.