Adaptive Modifications in the Leg Structure of Some North American Warblers

Abstract

Adaptive radiation is reflected in the correlation of foraging habits and mensurations of the pelvic skeletal appendages of five species of parulid warblers. The Black-throated Green Warbler, a general crown foliage gleaner, is considered the most generalized of the group. The Yellowthroat is adapted to a reed-shrub-tall-grass habitat by means of a long pelvic appendage and long toes necessary for security of perch in this habitat. The Black-and-White Warbler, with shorter distal segments, a long hallux, and a considerable unaual arc, is at an advantage in clambering over the trunks and larger limbs of trees. The short pelvic appendage of the Ovenbird is compensated for by equilibrating tail-lifting and wing-flicking movements as it forages on a leaf-littered forest floor. A longer third digit in the Redstart, the only significant difference from the Black-throated Green, may aid in rapid take-offs in pursuit of flying insects. Adaptive radiation- in warblers as exemplified by variation in the hind limb appears to be quite extensive and reflects the spread of the group into many niches. Sympatry may well have reinforced such