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just starting to open. Warblers were so abundant we had to use our binocu- 
lars between bites. Wilson’s and yellows were among the most numerous, 
but first place went to bay-breasted and chestnut-sided. We estimated over 
one hundred of each. 
Tuesday, May 15th, after four days of continual birding, we made a short 
trip to Thatcher Woods and were rewarded by seeing the very rare black 
swift, rare even on the Pacific coast — to be described in the next issue of 
the Bulletin. May 16th we went to the Indiana Dunes, where the vegetation 
was much further advanced. Warblers were numerous but hard to see. On 
the 17th we were at the Babson Estates, St. Charles, II]. Winds were wester- 
ly, mertensia in bloom, leaves backward. The wave was definitely on the 
wane. Though we saw seventeen species of warblers, only the chestnut- 
sided was abundant. We did have close views of a Swainson’s hawk. 
On the 18th we went to Meyers Road Swamp and were rewarded with 
two King rails, one of which came out on the road edge and squawked for 
5-10 minutes. On the 19th we birded at the Arboretum, Meyers Swamp and 
York Woods. Abundance and variety were good, but like the 18th, the 
“wave” was declining. At York Woods we watched a mixed flock of warblers 
move through the bare oak tops. Sunday the 20th most of the migrants 
seemed to have gone and already the resident bird population was settling 
down. 
During the week we had been aware of great bird movement in our own 
yard. Rose-breasted grosbeaks came to the feeders and bird baths as never 
before. Warblers bathed in numbers at our dripping bath, especially be- 
tween 6 and 7 p.m. During that hour the bath had one or more birds flitting 
around it all the time. We had excellent views of female bay-breasted, Cape 
May and blackpoll warblers. Canada warblers played on the lawn, run- 
ning after insects and hopping straight up into the air to catch them on 
the wing. 
We received many telephone calls during the week from excited people 
wanting some bright bird identified or an antic explained. Some twenty-five 
birds were brought dead to us in the classroom at the Arboretum, includ- 
ing a long-billed marsh wren picked up in someone’s yard. 
Species unusually common this spring were red-headed woodpeckers (we 
saw 22 whereas we usually see 2 or 3), olive-sided flycatchers (8 whereas 
we usually see 1), scarlet tanagers, and white-crowned sparrows. Among 
the warblers the chestnut-sided, bay-breasted, (at least the one big’ flock), 
Wilson’s, Mourning, and Canada were above the average of other years. 
Species conspicuously less common than usual were white-breasted nut- 
hatches, and among the warblers — palms, Tennessees, and _ black- 
throated greens. 
What causes such a phenomenal migration? We do not know too much 
about it. Probably the long, cold spell with adverse winds had grounded 
the birds in the Gulf States. Then on May 11th a mass of warm air moved 
up from the Gulf with strong southerly winds, and the birds flew with it. 
In one week as many birds arrived as usually do in three. But it was more 
than that, for the birds must have been grounded again in the Great Lakes 
area and in New England (where a similar migration took place). Why 
