Diurnal Rhythm of Attentiveness of Incubating Female Tree Sparrows (Spizella Arborea) at a Northern Latitude

Abstract

DIURNAL activities of female passerine birds in arctic and subarctic environments have not been extensively studied, although the subject is of great theoretical interest in discovering the nature of circadian rhythms and how they are influenced by environmental factors during breeding periods. Much has been written describing the diurnal activity of male passerines in continous daylight (Armstrong, 1954; Brown, 1963; Cullen, 1954; Franz, 1948; Hoffman, 1959; Palmgren, 1949; Wagner, 1958). Some of these authors, namely Armstrong, Hoffman, and Wagner, were stimulated to collect information on feeding rhythms during the nestling stage by Karplus' (1952) and Baumgartner's (1937) theses that nestlings in the arctic mature more quickly than those of the same species in temperate regions. However, information on activity of incubating females is sparse. Kuusisto (1941) obtained some data on the diurnal rhythm of activity of incubating female Willow Warblers, Phylloscopus trochilus acredula, and of the effect of the temperature and continuous daylight on their activity. The rhythm of incubation activity was studied in female Tree Sparrows (Spizella arborea) at Eagle Creek, 105 miles northeast of Fairbanks, Alaska (65025' N, 145032' E). In this species only the female builds the nest and incubates, although the male participates in feeding the young. Other pertinent information on the breeding biology of Tree Sparrows and a description of the habitat of the study area have been presented elsewhere (Weeden, 1965). From 15 May to 27 July there is continuous civil twilight between sunset and sunrise. On these dates the sun is below the horizon 5.28 hours, while at the June solstice it is below the horizon 2.00 hours. However, the study area is situated in a steep valley so that the light intensity is lower there than on the hilltops of the same locality. The aspects of female activity most readily studied are nest attentiveness throughout the day, length of the night rest, and restlessness while the females are attentive at the nest. The environmental conditions most likely to have a bearing on these aspects of female activity are day length and temperature. Day length profoundly affects the activity pattern of males (Franz, 1948: 317). Franz also pointed out that males and females of a species respond slightly differently to the light factor in temperate regions. Is this difference in sexual response to light augmented or minimized under conditions of continuous daylight? Temperature influences incubation activity of some passerine species in temperate regions (Hann,