| dc.description.abstract | I investigated the amount of time spent on foraging by birds in a successional white
spruce community, during semi-monthly time blocks, in the context of flying, singing and other
activities. Five hypotheses were tested: 1) cumulative amounts of time spent on foraging and
other activities by birds vary throughout the breeding season and among species; 2) bird species
differ in the mean amount of time spent per event on different activities; 3) birds spend more
cumulative time in the study area foraging on spruce than on other plants; 4) birds capture more
prey on spruce than on other substrates; and 5) prey capture rates differ among species. All bird
actions on the study area that were observed with binoculars were counted, timed and recorded.
Data for White-throated Sparrow, Song Sparrow, Lincoln’s Sparrow, Clay-coloured Sparrow and
Savannah Sparrow were analysed. Cumulative foraging times among periods were not
significantly different in 1991, but differed for White-throated Sparrow in 1992. Mean foraging
times differed only in late July 1992 for White-throated Sparrow and Clay-coloured Sparrow.
Foraging, except for Savannah Sparrow, occurred mostly on white spruce, but use of tree species
differed among periods in both years. Spruce budworms were most commonly taken between 15
June and 15 July in 1991 and 1992. Prey capture rates differed significantly among bird species
in late June 1991, in late June 1992 and early July 1992. Therefore, each hypothesis was
supported, but not in each time period. Such variations in bird activities during the breeding
season reflect breeding stage and changing ecological conditions. 1 concluded that sparrows
foraged similarly when spruce budworm was most easily obtained. These results were obtained
only by the method of dividing the breeding season into time blocks, and by recording time
durations rather than counts of events. I recommend that including variables in time as well as
space be the new norm in studies o f avian life history dynamics. | |
