In a study in 2003, Powers et al. investigated differential use of torpor in territorial and non-territorial hummingbirds from Arizona. The territorial and dominant species, Lampornis clemenciae, which will not let other hummingbirds feed in its territory and two subordinant and non-territorial species, Archilochus alexandri and Eugenes fulgens, were tested for their use of torpor under normal feeding conditions. The researchers collected birds from their natural habitat where all three species occurred concurently. Then they tested their use of torpor (see figure 2.)and use of body-fat stores.

Powers et al. discovered that the more dominant bird, L. clemenciae, used torpor less frequently than the two subordinant species. They hypothesized that this would be the case because L. clemenciae has unrestricted access to food sources and therefore should have enough energy intake to not need to enter torpor. This hypothesis was tested by observing the body fat concentrations in all three species. L. clemenciae had much higher overall body fat and used more fat mass each night than did the other two species.

This study indicates that extensive use of torpor may also be an adaptation to deal with high competition from other species. Since both A. alexandri and E. fulgens must use less optimal foraging strategies than L. clemenciae, they use torpor more frequently to better conserve the energy that they are able to collect through their sub-prime foraging strategy.

Figure 2. Proportion of Lamporonis clemenciae, Archilochus alexandri, and Eugenes fulgens that entered torpor during experimental trials. Adapted from Powers 2003.