Buff-bellied Hummingbird Bill Color Variation by Age, Sex and Season
By Brent Ortego
Measurements of color variation in upper mandible of Buff-bellied Hummingbird (Amazilia yucatanensis) were taken from a population of 500 banded and 450 recaptured Buff-bellied Hummingbirds at Raisin, Victoria County, Texas from August 1995 through June 2001. This population was male dominated and was made up of 83% males. Adult Buff-bellied Hummingbirds normally have a red base and distal black tip on the upper mandible. The variation of color between sexes and ages has not been reported in the literature. Adult males in this study had at least 80% of upper mandible red during breeding season while adult females had 50-60% red. During winter there was overlap of percent red with adult males having from 40-60% and adult females 40-50%. Young of both sexes typically had no red until August with gradual increases until about 20% in November when the amount of red advanced fairly rapidly to where second year males had 40% red in January as compared to 60% in adult males. The color of second year birds was the same as adults by April. The sample size for second year females was too small to draw conclusions. Another difference between bill coloration in the sexes was that the upper mandible color of adult males was typically bright red while females was a duller blood red.
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