How Birds Control Insect Outbreaks

Control of outbreaks of insects. One feature of birds that makes them such a successful check upon insects is their power of flight. Wherever insects are found in unusually large numbers, there birds quickly gather to prey upon them. When the Mor­mons first settled in Utah, their crops were attacked by the crickets and nearly destroyed, until the gulls came in large numbers and preyed upon the crickets and saved the remainder of the crops. In commem­oration of this, a monument to the gulls has recently been erected in Salt Lake City.

Outbreaks of locusts in the Middle West have been controlled by birds. A serious outbreak of the forest tent-caterpillar occurred in New York and New Eng­land in 1897-98, but was finally brought under con­trol by the action of the birds. An outbreak of the canker-worm occurred in an apple orchard in Illi­nois.

A study of the birds found here showed that twenty-six kinds of birds were feeding on these canker-worms, which formed thirty-five per cent of the birds' food. There are many other records of small local outbreaks which have been controlled by the birds. But yet the greatest service that the birds render is in keeping the insects down to such a point that outbreaks do not occur.

Division of labor. The division of labor in those places where insects are found is well apportioned among the birds. Some birds, like the sparrows, feed upon the insects found on the ground; the wood­peckers spear those in the bark and wood of trees; warblers and vireos glean the small insects found on the leaves, while the larger birds, like the cuckoos, feed upon the larger insects found on the foliage; the swallows prey upon the insects in the air.

"Birds of a Maryland Farm." The figures so far given regarding the food habits of birds have been based largely on the averages for many birds col­lected from all parts of the country. But in some cases, in order to determine the value of birds in a particular locality, certain local facts regarding the crops raised and the insects present must be ascer­tained in order to decide definitely the economic status of the birds found there.

Dr. Judd, of the Bureau of Biological Survey, made a careful study of a single farm of about two hundred and thirty acres in Maryland, in order to ascertain which birds were valuable and which were injurious on this particular farm. The farm was visited frequently during every month in the year for a period of seven years.

A list of the available food-supply was made, consisting of insects, seeds, and fruit; the crops grown were noted, and the insects preying upon them. The birds were studied with reference to the kinds found, the abundance of each kind, their distribution, and es­pecially with reference to their food habits.

The birds were first studied in the field to ascertain on what they were feeding, and a few birds were shot and the contents of their stomachs examined. This study is one of the most valuable ever carried on along this line, and the results have been published in a bulletin entitled "Birds of a Maryland Farm."

The results found here so nearly parallel the gen­eral conclusions drawn from a study of birds through­out the whole country, that a brief summary may be given. During this period 168 species of birds were observed. The stomachs of 298 birds were collected and examined. Considering the food of all the birds collectively, exclusive of the English sparrow, it was found that beneficial insects formed 4 per cent of the food, while injurious insects formed 27 per cent; grain formed Ii per cent, while weed seeds formed 18 per cent.

The injurious food is thus seen to equal in amount nine times the beneficial food; or, in other words, the birds did nine times as much good as harm. A small amount of cultivated fruit was eaten, but the exact per cent was not given in the bulletin.

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