578 Wisconsin Academy of Sciences, Arts, and Letters. 
This Tern, too, nests in colonies though these are not often of 
so great extent as those of the Forster’s Tern. Most of the nests 
of this bird were found in grassy sloughs, from six to fifteen 
being the number of nests in a colony. They were placed on 
masses of dead grass, reeds, or other vegetable substance, floating 
among the grass or reeds of the slough. The material used in 
building the nests is generally grass, but, when the nest is sit¬ 
uated in a reed and rush grown slough, the material used is small 
pieces and bits of rushes with a lining of finer material. A 
slight depression in the top of the pile serves to keep the eggs 
from rolling off into the water. An average of several nests 
measured is: diameter, outside, seven inches, inside, three and 
three-fourths inches; depth, outside, one and one-half inches, in¬ 
side, one inch. Some of the nests observed were very flimsy 
affairs, apparently only a slight hollow being scraped out in a 
mass of floating debris. Unlike the Forster’s Tern, no nests 
of the Black Tern were found placed in very close proximity to 
each other. Elach nest had its own little area, at a distance of 
several feet from the other nests of the colony. Like the Fors¬ 
ter’s Tern, these birds also make a great disturbance when their 
breeding grounds are approached. One day when a duck was 
shot in the neighborhood of a, colony of Black Terns, these birds 
immediately gathered in numbers and hovered about above the 
wounded duck, making a great disturbance until the bird ceased 
splashing in the water. 
At Water-hen Lake, the Black Tern could be seen at all hours 
of the day, flying up and down over the rushes bordering the 
shore, in search of food. In the evening they habitually came 
ashore and flew about over the fields in great numbers, apparently 
after the mosquitoes which were particularly numerous at that 
time. Sometimes they were seen to gather near one spot along 
the shore of the lake, and circle about in the air like a swarm of 
bees. 
The number of eggs laid by this bird is generally three, but 
nests were found containing only two eggs, in which incubation 
had commenced. A few nests were found containing four eggs, 
the eggs of a nest bearing a close resemblance to each other. Al¬ 
though it is possible that the eggs of such sets were laid by more 
than one bird, it seems probable that the Black Tern occasionally 
lays four eggs at one brooding. The eggs of this bird are too 
well known to need description here. The first nests containing 
