4 
a chance to estimate their numbers. Several experienced field naturalists, on being 
asked their opinion as to the number of birds breeding within this state, agreed that 
three to the acre would be a conservatave estimate. This would mean about fifty-four 
million pairs; each nest will contain say, on an average, five young, and most birds 
raise more than one brood in the season; so, even allowing for the great destruction 
of eggs and young, the number of birds’ mouths to be fed, during the summer 
months, on the farms of Illinois, must amount to hundreds of millions. 
Before the summer is past the migratory movement again shows itself. Each 
night that a cool north wind is blowing the flights of birds pour into our state. It 
is probably about the 1st of September that our bird population has reached its maxi¬ 
mum, but still they come and go, and the last red leaf of autumn has fallen before 
the waves cease to sweep over our land. How many birds, in this annual cycle, have 
lived within our state we cannot estimate; but surely the number is enormous, and 
not the smallest patch of ground, not a single tree or shrub, remains unvisited. 
Birds are fast livers. Their activities are immense ; their hearts beat twice 
as fast as those of man ; the temperature of their blood would be to us fever heat. 
To support such vitality a relatively enormous amount of food is required ; and 
this, too, of the most nutritious kinds, such as grain, seed or animals. Even a 
greater amount than is consumed by the adult is needed by the young, for while 
in the nest the rate of growth is very great. As an example of this we may take 
some recently published observations on the.growth of a nest of young song-spar¬ 
rows. Each day the brood was carefully weighed and the increase noted. During 
the first day the average gain in weight of the nestlings was forty-eight per cent, 
and in six days their weight was very nearly trebled. Such growth needed indeed 
the constant attention of the parent birds, who, on an average, visited the nest at 
intervals of from two to five minutes from daybreak till dark. Take our fifty-four 
million pairs of breeding birds within the state of Illinois, say that one-third of 
these have young at any one time, let the parents visit the nest with food every 
five minutes ; the bases we take are conservative enough, yet it means thirty-four 
hundred million meals furnished to the infant birds of the state each day during 
the breeding season. 
Professor Treadwell has recorded the case of a young robin that he kept in 
confinement and fed on earth worms. The weight of the bird was taken each day 
and also that of the food consumed. He found that it lost in weight though he in¬ 
creased the daily allowance from ten to fifteen, twenty-four, twenty-five and thirty 
worms; it was not until the fourteenth day when he gave it sixty-eight worms 
weighing thirty-four pennyweights that the bird throve and increased in bulk. On 
that day the bird itself weighed twenty-four pennyweights, so that it consumed 
forty-one per cent more than its own weight in twelve hours. 
The amount of food that has to be supplied by the old birds might well in¬ 
spire human parents with horror and consternation. Yet so rapid is the growth of 
the nestling, so intense the vital fire within its little body, that it is evident even 
this quantity would not suffice unless it were of the most nutritious kinds. Of the 
more essential food constituents, such as proteids and carbohydrates, fruits contain 
a very small proportion and these substances must be sought elsewhere ; and hence 
the young birds’ food must of necessity, and as proved by observation, does consist 
principally of soft-bodied insects. 
About the first extensive scientific work on the relation of birds to agricult¬ 
ure and horticulture was done within our own state by our present state entomol- 
