Aggressive Behavior by a Migrating Cape May Warbler

Abstract

Vol. 84 reported for several regions (see references in Orians and Willson, op. clt.) and probably reinforces the tendency toward separation of activity centers. Miscellaneous.-Interactions of other species nesting in the marsh were observed occasionally; I will mention these but briefly, since the value of isolated observations of aggressive behavior is small. Occasionally Song Sparrows and marsh wrens held adjacent territories in wet meadowland beside the Concord marsh. Foraging areas tended to be quite separate and male Song Sparrows were sometimes aggressive toward trespassing marsh wrens. Two Yellow Warbler (Dendroica petecMa) nests were located in the Concord marsh; one was in a thick stand of marsh grass, the other on a weedy tussock. The adults foraged mostly on shore and were seldom encountered by other marsh-nesters. Another pair of Yellow Warblers nested on shore but sometimes foraged on the marsh; the Swamp Sparrow on whose territory they trespassed usually chased them away. Yellowthroats (Geothlypis trichas) sang frequently from the bushes at the marsh edge and the small trees in a wet meadow near the marsh, and occasionally they flitted a short distance out into the marsh to forage. A Swamp Sparrow pursued a neighboring Yellowthroat in a vigorous and extended chase in a wet meadow with scattered shrubs.•MAR¾ F. W•LLSON, Department o] Zoology, Vivarium Building , University of Illinois, Champaign, Illinois. Aggressive behavior by a migrating Cape May Warbler.-During periods of adverse weather or winds, many migrants are forced to land on the Dry Tortugas, a group of small islands located in the Gulf of Mexico approximately 70 miles west of Key West, Florida. Most of them move on as soon as weather conditions permit. However, because of depleted energy reserves many are forced to remain and search for food and water, both scarce commodities on these dry sandy keys. Birds may be seen feeding on the well-mowed lawns about Fort Jefferson and among the windrows of rotting turtle grass (Thalassia testudlnum) drifted along the tide lines. Many fall prey to avian predators (see R. Cunningham, Auk, 82: 502-503, 1965) or die of starvation. On 8 May 1965, on Garden Key, I observed a male Cape May Warbler (Dendroica tigrlna) chasing other birds away from the flowering stalk of a century plant (Agave sp.) which was growing close to the outer wall of Fort Jefferson. The flowering portions of the stalk were at the level of the second floor casemates of the fort, at least 30 feet above ground level. The Cape May Warbler, presumably the same male each time, was seen chasing individuals of both sexes of its own species as well as Blackpoll Warblers (Dendroica striata), Myrtle Warblers (D. coronata), Black-throated Blue Warblers (D. caerulescens), Palm Warblers (D. palmarum), Yellow-throats (Geothlypis trichas), and Redstarts (Setophaga ruticilla) during brief periods of observation several times daily over a three-day period. Glen E. Woolfenden, Ruth Rogers, Doris Mager, and Sievert A. Rohwer also witnessed this activity. Aggressive behavior by the male Cape May Warbler was restricted to birds that flew into the upper portions of the flower stalk. He did not attack any birds that were on the leaves growing from the base of the plant, on the ground, or in two large Australian pines (Casuarina equise'tifolia) standing a few feet away. After 11 May and until our departure on 13 May the male was not seen again and no further defense of the stalk by any bird was observed, although birds continued to frequent the flowers.