Abstract
Daily and seasonal movement patterns of the great-tailed grackle were studied in the Brazos County, Texas Region. Grackles were marked with individual color-coded tags or equipped with radio transmitters. Two types of movement patterns were discerned. In the first the bird flew each day from the roost to a specific area where the bird spent much of the day; this same locale was used anywhere from a few days to a few months, after which the bird would then shift to another locale. In the second type, more characteristic of large winter flocks, the grackles foraged over a much greater area, not adhering to any particular locale for long. Flocks were an open society and much flock organization and shifts to new areas were believed to result from interchange at the roosts. Closely examined with movement patterns were population and flock parameters. During the late spring and summer, when population was low, grackles, when not in the colonies, were scattered about in many small flocks. Female/offspring groups, upon leaving the colonies, coalesced into larger groups numbering about 30 or so birds. Later breeding males disbanded from the colonies and joined briefly with them. At this time residential grackles generally moved into the farm area of the Texas A&M University campus increasing flock size still more; populations were further swelled by fall and winter migrants invading the area. Such an influx could increase the grackle population 7 times. The number of large sized flocks increased while the number of small sized flocks decreased. In March and April these large flocks disbanded into smaller groups as the migrants returned north and residents dispersed into the surrounding residential areas to breed..
Hanson, Michael Terry (1976). Movement patterns, flock parameters, and habitat selection in the great-tailed grackle. Texas A&M University. Texas A&M University. Libraries. Available electronically from
https : / /hdl .handle .net /1969 .1 /DISSERTATIONS -613822.