EASTERN HOUSE WREN 129 



* * ♦ Under certain experimental conditions, the body temperature of a 

 house wren has been lowered to below 75° F. (23.9" C.) yet the bird recovered 

 when it was placed for a short time in a warm incubator. A body temperature of 

 71° F. (21.7° C.) is, however, lethal. 



High air temperature^s become significant only when they get as 

 high as 93° F. At air temperatures above this degree the resistance 

 time of the birds decreases, body temperatures may rise, the general 

 metabolism is abnormally disturbed, and the normal reproductive be- 

 havior interfered with. Birds have upper limits of temperature 

 tolerance as well as lower limits, and these .seem to be effective in con- 

 trolling distribution. 



Food. — As far as its feeding habits are concerned, the house wren 

 may be considered entirely beneficial to the interests of mankind. The 

 food is almost all animal life, the small amount of plant material found 

 in stomach examinations being purely incidental and taken in the 

 course of capturing insects poised on the vegetation. Much of our 

 knowledge of the food habits of the house wren is based on field obser- 

 vations, but the most precise information we have has been derived 

 from the detailed analyses of the stomach contents of individuals col- 

 lected in all sections of the distributional range of the species. 



According to Beal (1897), 98 percent of the food is made up of 

 insects or their allies and only 2 percent is vegetable matter. One-half 

 of the food consisted of grasshoppers and beetles, the remainder cater- 

 pillars, bugs, and spiders. The examination of 68 stomachs of house 

 wrens, reported in a later publication, by Beal (Beal, McAtee, and 

 Kalmbach, 1916) , substantiated the above findings. The largest four 

 items taken in order of their amounts are bugs, grasshoppers and 

 related forms, caterpillars, and beetles. The bugs, made up chiefly 

 of stink bugs, negro bugs, and leafhoppers, constituted 29.34: percent 

 of the food. Grasshoppers, crickets, and locusts are represented in the 

 food throughout the season and aggregate 17.61 percent of the food. 

 Moths and caterpillars, including such forms as cabbage worms and 

 gypsy moths, make up 13.9 percent, and beetles trail closely in amount 

 at 13.8 percent. Ants are eaten to the extent of only 8 percent of the 

 yearly food, but during March they are more significant, being repre- 

 sented in that month by 22.67 percent. Bees, wasps, and flies are 

 taken in smaller amounts ; evidently these types of insects are left for 

 the fleeter flycatchers and swallows. Spiders are very acceptable and 

 are captured every month in the season. The latter are found by the 

 inquisitive wrens while searching and exploring under piles of lumber 

 or brush, stone walls, hollow logs, outhouses, and sheds. Only a mere 

 3 percent of the insects eaten can be considered useful as enemies of 

 destructive species of insects. 



