Breeding Behavior of Yellow-Bellied Sapsuckers

Abstract

This communication presents aspects of the nesting of Yellow-bellied Sap-suckers (Sphyrupicus warius) either not mentioned in previous accounts (Bent 1939; Johnson 1947; Howell 1952; Kilham 1962a, b; Lawrence 1967) or, if mentioned, open to amplification and new or other interpretation. Activities covered extend from the start of excavating through egg-laying and incubation to fledging. They do not include agonistic and courtship behavior which are being described separately. METHODS With 5 pairs studied in special detail and 4 others for a more limited time, I made observations from l/2 to 2 hours a day every day, with a few missed from late April or early May through fledging in July, either between 08:00-10:00 or 15:0&17:00, these times having been found to be equivalent in terms of heights of activity. Percentages of time that the male or the female of a breeding pair spent in such activities as incubation or brooding refer, as shown in Tables 1 to 4, to total observation times, a method also used by Lawrence (1967). They are given for convenience of description and are not intended to imply total coverage that would have demanded dawn to dusk observations 7 days a week throughout the nesting period. In addition to counted hours (281) I spent many uncounted ones in partial observations on 12 other nesting pairs in Lyme, New Hampshire. In regard to attentiveness I have not used methods employed, among others, by Stickel (19651, Lawrence (19671, and Skutch (1969). Stickel, who gives the most detail, designates "attentiveness as the time adults spent excavating a cavity, sitting beside it, guarding and incubating eggs, and once the birds had hatched, as that time the parents remained at the nest cavity." What Stickel refers to as sitting by a nest, guarding it, etc., I have considered under the general term of "loitering." Only those times, therefore, that the sapsuckers actually spent in the work of excavating, sitting on eggs, or brooding young within the nest, have been considered in making calculations. A session at the nest, in contrast, has been regarded as the total time that one of a pair spends in or by the nest until relieved by its partner. Descriptions of the vocalizations, drummings, tappings, and displays of S. varius mentioned in this report are given elsewhere (Kilham 1962a). EXCAVATION Share done by males and females.-The amount of work done by either sex depends on circumstances. At 5 nests that were first excavations of the breeding season, I found that the males did nearly all of the work. When they excavated, they worked continuously from 15 to 30 min at a stretch. When females changed places with them they spent much of their time in preening and resting as Lawrence (1967) has described. Their excavating was often token in character, with little sawdust removed, particularly after completion 310