US Geological Survey


Date of this Version



THE PRAIRIE NATURALIST , vol. 8, nos. 3 & 4 (Sept-Dec. 1976)


Migrating passerines frequently encounter adverse weather during their northward movements in early spring. Inclement weather often causes temporary halt of migrating passerines short of their destinations (Curtis 1969). In May 1974, such a grounding of spring migrants occurred in southwestern Manitoba due to unseasonable weather. Many insectivorous birds became weakened or died of starvation as a result of exposure to low temperatures, depletion of fat reserves, and lack of available food.

Arrival of Spring Migrants

The first large influx of insectivorous birds, mainly Myrtle (Dendroica coronado coronata) and Yellow (Dendroica petechia) Warblers, was noted on 19 May 1974 at Minnedosa, Manitoba. The migration continued through 21 May when daily counts at Delta, Manitoba, were highest. Most numerous were Least Flycatchers (Empidonax minimus), Myrtle, and Wilson's (Wilsonia pusilla) Warblers. Normally when these birds arrive in southern Manitoba during May they spend much of their time actively searching the aspen (Populus tremuloides) woodlands for food. In 1974, however, large numbers of Myrtle and Yellow Warblers were observed feeding in emergent stands of flooded cattail (Typha latifolia) and bulrush (Scirpus spp.) along the margins of ponds and sloughs. Arthur S. Hawkins (personal communication) reported "several hundred warblers, mostly Myrtles, in a quarter-mile stretch or less, and they appeared to be obtaining some kind of insect food from underneath the emerging sedge (Carex spp.) leaves." At Delta, Myrtle and Wilson's Warblers were observed feeding in a similar manner in flooded white-top (Seoloehloa festueaeea). Near Minnedosa, Myrtles reached densities of 15-20 per acre and usually were observed actively feeding in fields and wetlands. Some individuals were easily captured by hand and were obviously weak