Plumage Characteristics of Juvenile Black-Chinned Hummingbirds

Abstract

Various criteria useful in separating adult female and juvenile Black-chinned Hummingbirds (Archilochus alexandri) from similar species under favorable field conditions were discussed by Stiles (1971). My purpose here is to describe juvenal plumage characteristics of A. alexandri that appear to be reliable indicators of sex, and to present a key for age and sex determination in this species. Plumages of Black-chinned Hummingbirds do not appear to have been studied in detail, as have those of Anna's Hummingbird (Calypte anna; Williamson 1956) and Selasphorus species (Aldrich 1956, Stiles 1972). Ridgway (1911) described juveniles as similar to adult females but with dorsal feathers terminally margined with buff, and throat coloration in juvenile females as immaculate, or with dusky spots and streaks smaller and less distinct than in juvenile males. Stiles (1971) stated that the throat coloration of adult females is highly variable and that the throats of juvenile males average darker than adult females, while juvenile females are less heavily marked. Short and Phillips (1966) observed that females have acutely pointed inner primaries (3-7) but that the subterminal notch is less distinct than in males. Stiles (1971) noted that the outer rectrices of adult females are bluntly pointed, and added that juveniles may lack this characteristic. Between August 1978 and September 1981, I netted, banded, and released 212 Black-chinned Hummingbirds near Three Rivers, Tulare Co., California. The outer rectrices, fourth and fifth primaries (counting from inside), and representative feathers from the dorsum, throat, and primary coverts were obtained from 73 adult females and juveniles. These feathers were placed on notecards, along with band number, date, measurements, and other plumage notes. The degree of culmen corrugation (Ortiz-Crespo 1972) was also noted. In analyzing these data, I separated adults from juveniles by the lack of culmen corrugations in the adults and by plumage characteristics (throat coloration of adult males and the absence of buff margins on dorsal feathers of adult females). Measurements of adults are summarized in Table 1. All individuals determined to be adult females had a pointed fifth rectrix, though the degree of emargination and/or acuteness varied (Fig. la). In addition, the fourth and fifth primary remiges had a faint notch near the pointed, subterminal end of the inner web (Fig. Id). Throat coloration was variable. Some individuals had immaculate throats (feathers with dark rachis and whitish webs; others had dark throats (feathers with rachis and webs entirely dusky except for a narrow white margin). Individuals in juvenal plumage had buff margins on dorsal f athers (and on the primary coverts) and corrugations on the rhamphotheca of the upper mandible. Of 30 juveniles, I determined the sex of 24 (17 females, 7 mal s) by a conservative evaluation in which culmen characteri tics (amount of corrugation and length) and, if present, purple feathers in the throats of juvenile males, were the primary factors considered. Six individuals could not be sexed with certainty on the basis of these characteristics. In comparing the fifth rectrix and the fourth and fifth pr maries between males or females (sex determined by the above criteria) I noted that males invariably had a pointed fifth rectrix (Fig. lb), although the degree of emargination and/or acuteness varied. Also, the fourth and fifth primary remiges were pointed, with a faint notch on the subterminal end of the inner web (as in adult females). Females invariably had a more broadly rounded fifth rectrix (Fig. Ic) than males and their primaries were rounded on the subterminal end of the inner web (Fig. le). One f male had apparently lost several outer rectrices on one side and replaced them: on one side, the outer rectrix was rounded (juvenal) while the corresponding rectrix on the other side was pointed (adult). A juvenile female with ounded outer rectrix and subterminal end of the inner web of the fifth primary was banded in 1979. When she was recaptured in 1981, the outer rectrix was acute and the fifth primary was pointed, with a faint notch at the subterminal end of the inner web. At both encounters her throat was immaculate.