How Birds Keep Insects and Weeds in Check

Vitality of weed seeds. And then, finally, after the seeds have reached their resting-places, they may retain their vitality and be able to germinate after many years of exposure to winter cold and summer drought. The seeds of most of our common weeds retain their vitality from three to five years. The mustard seeds may retain theirs for ten years. In one study made on the longevity of seeds, some seeds of the Indian mallow and shoo-fly germinated after a lapse of fifty-seven years, and the seed of white sweet clover after seventy-seven years.

Birds as destroyers of weed seeds.

We have already seen that another enemy of the farmer is the insect, and it is a very interesting and remarkable fact of vital importance to the farmer that one of Nature's means of controlling both these pests is the same, namely, the birds. Sometimes one group of birds helps to control the insect pests, and another group helps to control weed pests, but in many cases the same birds help to control both insect and weed pests, as is the case with the native sparrows. In fact, in the great majority of cases those birds which feed upon weed seeds also feed upon insects, al­though there are many birds which feed upon insects that do not eat weed seeds.

There are two or three hundred kinds of birds known to eat weed seeds to some extent, and about one hundred kinds of weed seeds are known to be eaten. The birds which are most effective in con­trolling weeds are the bob-white, the mourning dove, and the native sparrows. The seeds most commonly eaten are those of ragweed, pigeon-grass, crab­grass, bindweed, purslane, smartweed, pigweed, and lamb's-quarters,

As birds are capable of eating enormous quantities of insects, so, too, some eat enormous quantities of weed seeds. It is common for a crow blackbird to eat from thirty to fifty seeds of smartweed, and a field sparrow one hundred seeds of crabgrass, at one meal. Dr. Judd estimated that on an acre of land on a Maryland farm, the 540 birds found there destroyed 46,000 weed seeds at a single breakfast.

Mr. E. H. Forbush, during one winter, fed the birds at his window with seeds of Japanese millet, a sort of weed improved by cultivation, whose seeds are larger than those of most weeds. Records were kept of the number of seeds eaten in a certain time. It was found that the three species feeding averaged each to eat thirty-five seeds per minute. Assuming that each bird fed on weed seeds at this rateIor only one hour a day, it would destroy 14,700 weekly.

Professor Beal estimates the amount of weed seed annually destroyed by the tree sparrow in Iowa as follows: ­

On the basis of one fourth of an ounce of seed eaten daily by each bird, and an average of ten birds to each square mile, remaining in their winter range two hundred days, there would be a total of 1,750,000 pounds, or 875 tons, of weed seed consumed in a single season by this one species. Large as are these figures, they unquestionably fall far short of the reality.

Effect on weed-patches. Studies that have been made of patches of weeds after being visited by birds show that the work of destroying the seeds is done very effectively by them.

In April, Dr. Judd exam­ined weed-patches on a farm in Maryland to see to what extent the seeds had been destroyed. In one field, where in the fall there had been scores of seeds on every ragweed plant, it was difficult to find, during a fifteen-minute search, half a dozen seeds remain­ing. In another field, in a thick growth of pigeon­grass, where there had been hundreds of seeds in the fall, sometimes not a single one was found; and on a mat of crabgrass, where there had been thou­sands in the fall, frequently not one was left.

The native sparrows are specially efficient de­stroyers of weed seeds, and sometimes in two months will destroy ninety per cent of the seeds of pigeon­grass and ragweed. Weed seeds form more than half of their food for the entire year, and during the colder

Professor Beal estimates the amount of weed seed annually destroyed by the tree sparrow in Iowa as follows: ­

On the basis of one fourth of an ounce of seed eaten daily by each bird, and an average of ten birds to each square mile, remaining in their winter range two hundred days, there would be a total of 1,750,000 pounds, or 875 tons, of weed seed consumed in a single season by this one species. Large as are these figures, they unquestionably fall far short of the reality.

Effect on weed-patches. Studies that have been made of patches of weeds after being visited by birds show that the work of destroying the seeds is done very effectively by them.

In April, Dr. Judd exam­ined weed-patches on a farm in Maryland to see to what extent the seeds had been destroyed. In one field, where in the fall there had been scores of seeds on every ragweed plant, it was difficult to find, during a fifteen-minute search, half a dozen seeds remain­ing. In another field, in a thick growth of pigeon­grass, where there had been hundreds of seeds in the fall, sometimes not a single one was found; and on a mat of crabgrass, where there had been thou­sands in the fall, frequently not one was left.

The native sparrows are specially efficient de­stroyers of weed seeds, and sometimes in two months will destroy ninety per cent of the seeds of pigeon­grass and ragweed. Weed seeds form more than half of their food for the entire year, and during the colder half of the year they form about four fifths of the food of some sparrows. Most of the work of destroy­ing weed seeds is done between early autumn and late spring. During the summer the birds feed largely on insects.

Mr. H. W. Henshaw, chief of the Bureau of Bio­logical Survey, estimates that in the year 1906 the weed-seed-eating birds saved to the farmers of the country $85,000,000, on the assumption that the de­struction of these weed seeds resulted in the saving of only one per cent of the crop.

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