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We compared the field metabolic rate (FMR) and behavior around sugar-water feeders of sympatric territorial and non-territorial hummingbirds in the Chiricahua Mountains of southeastern Arizona during July 1987 and 1989. The territorial species was the Blue-throated Hummingbird (Lampornis clemenciae; mean mass 8.77 g) and the non-territorial species the Black-chinned Hummingbird( Archilochusa lexandri; mean mass 3.67 g). FMR (CO2p roduction)a nd watert urnoverw erem easuredu singt he doublyl abeledw ater technique. FMR averaged 81.7 kJ/day (n = 4) in L. clemenciae and 29.1 kJ/day (n = 4) in A. alexandri. Mean mass-specific FMR was higher in L. clemenciae (18.36 ml CO2 g-' hr-') than in A. alexandri (15.58 ml CO2 g-' hr-'). This might be due to higher activity costs associated with the aggressive territorial behavior of L. clemenciae.Water influx averaged 1,734 ml kg-' day-' in L. clemenciae (n = 5) and 1,728 ml kg-' day-' in A. alexandri (n = 6). These values represent turnover rates equivalent to 185% and 245% of body mass per day respectivelya nd arec onsistentw ith measurementsm ade on otherh ummingbirds pecies. Where these species coexist in the Chiricahua Mountains, L. clemenciae is a dominant territorials pecies whereasA . alexandria ppearst o be non-territoriala, cquiringe nergy by robbing nectar from L. clemenciae territories. Lampornis clemenciae is highly aggressive againstc onspecifics,b ut appears to ignore intruding A. alexandri. Lack of territorial defense behavior in A. alexandri might reduce field energy expenditures and contribute to a lower FMR than L. clemenciae. We hypothesize that the lack of territorial aggression by L. clemenciae against A. alexandri is due to the high quality, abundance, and predictability of their food source which eliminates the profitability of such aggression. We also suggest that the intense aggression exhibited by L. clemenciae towards conspecifics might be motivated by factors relating to fitness other than defense of a food source.


Originally published in The Condor, 96:141-150.
© The Cooper Ornithological Society 1994

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