Seasonal Changes in Use of Torpor
Rufous Hummingbird, used with permission from John English.
|In several different species of hummingbirds, seasonal changes in torpor use have been observed. Seasonal changes have been observed in hummingbird species from locales as different as the Andes Mountains (Carpenter 1974), deserts of the Southwest United States (Calder 1994) and the Rocky Mountains of the United States (Heibert 1993).|
In the species from the Andes, Oreotrochilus estella estella, field studies identified that torpor occurred more frequently and for longer durations during the winter months than the summer months (Carpenter 1974). Carpenter was able to rule out differential food availability as the cause of the heavier use of torpor, since some O. estella individuals had access to "copius nectar supplies", yet had the same torpor use patterns as the more calorie restricted birds. It was hypothesized that photoperiodicity may induce stronger use of torpor during the winter as a method to maintain energy stores for possibly longer and colder nights.
Calder and Heibert both noticed seasonal differences in use of torpor in their respective hummingbird species, Selsphorus platycercus and the rufous hummingbird. Research of S. platycercus indicated that topor was mostly necessary during breeding and wintering seasons due to shifting food supplies and in midseason periods for the same reasons (Calder 1994). Heibert found that captive rufous hummingbirds, in addition to using increased torpor in the Autumn to conserve energy for migrations that they could not take, used reduced torpor during their molting period in the Spring (Heibert 1993). This reduced use of torpor in the Spring may be connected with decreasing the amount of time needed for molt, since the process will continue througout the evening and not just at night.
Back to uses of Torpor
Section Three: Mechanisms of Torpor
This website was created as a part of a class project in the Animal Physiology Class at Davidson College.
Questions? Contact the site designer