86 BIRD FRIENDS 



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, al- 

 though 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 con- 

 trolling weeds are the bob-white, the mourning dove, 

 and the native sparrows. The seeds most commonly 

 eaten are those of ragweed, pigeon-grass, crab- 

 grass, bindweed, purslane, smartweed, pigweed, and 

 lamb's-quarters. 



