By observing rufous hummingbirds revisiting flowers that refill with nectar at regular intervals, researchers have found that these birds can remember when they last visited individual flowers. This so-called "interval timing" is an ability that has received much attention in the laboratory, where it has been shown that animals can learn to time one or two short intervals (on the order of seconds to 1½ hours). However, almost nothing had been known about whether animals in the wild can do this in the course of their normal behavior.
The new findings are reported in the March 7th issue of Current Biology by Dr. Susan Healy of the University of Edinburgh, Dr. Andrew Hurly of the University of Lethbridge, and colleagues.
Hummingbirds that defend territories containing many flowers can remember which flowers they have visited. Because many flowers refill their nectar supplies, it would be very efficient if a territorial hummingbird could also remember when it last emptied a specific flower, so as to plan when to return to next harvest nectar. Returning too early would result in a wasted trip. Returning too late might result in another animal's taking the nectar. Thus, accurate measures of time intervals would support efficient harvesting of nectar.
In the new work, the researchers found that free-living hummingbirds tested in their breeding territories in the Canadian Rocky Mountains have timing abilities that are considerably more impressive than those that have been shown previously in the laboratory. Not only were the hummingbirds able to remember how long it had been since they had last emptied a flower, but they could also keep track of the time since the last visit to eight different flowers, and could continue to do this through the course of a day. In essence, these birds can maintain, over long periods of time, at least eight independent stopwatches, each of which is started by a visit to a particular flower and is reset when the bird next empties that flower.
The work shows that animals in the real world are capable of more impressive timing feats than have been previously considered. The findings also suggest that animals may be capable of planning their future with some degree of precision.
The researchers include Jonathan Henderson and Susan D. Healy of the University of Edinburgh in Edinburgh, Scotland; T. Andrew Hurly of the University of Lethbridge in Lethbridge, Canada; Melissa Bateson of the University of Newcastle in Newcastle upon Tyne, United Kingdom.
This work was supported by the National Sciences and Engineering Research Council (T.A.H.) and the National Environment Research Council (J.H. and S.D.H.).
Henderson et al.: "Timing in Free-Living Rufous Hummingbirds, Selasphorus rufus." Publishing in Current Biology 16, 512–515, March 7, 2006. DOI 10.1016/j.cub.2006.01.054 www.current-biology.com
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