By dint of much patient watching we got our data. In the dry season when insects were scarce and the grass short, it took an ani, hunting alone, two minutes on the average to find an insect. In the same length of time hunting with a cow the catch averaged three insects. Thus hunting with a cow as a beater was three times as effective as hunting alone.
The effect of the change of the season in abundance of food for the ani was very striking. In the wet season the grass began to grow fast, and insects became common. Then the anis had an easy time. Without a cow an ani averaged between three and four insects a minute, more than six times as much as in the dry times. There was less incentive to use a cow as a beater, with food so abundant, but when the ani did so, its rate of finding insects was still higher: between four and five insects per minute. In a table it looks like this:
Average Number of Insects Per Minute Found by Ani Feeding
| WITHOUT COW | WITH COW | |
| Dry Season | .5 | 1.5 |
| Wet Season | 3.4 | 4.7 |
But the three-times-greater-results in a given time in the dry season do not tell the whole story as to the effectiveness of using a beater. When an ani was hunting by itself it walked about, covering a surprisingly large amount of ground. When using a cow as a beater, not only did it catch more insects in a given length of time, but it also walked about much less, saving a great deal of energy.
This is not true co-operation between cow and bird, for they're not working together toward a common end. It's not exploitation of the cow by the birds, for the cows lose nothing. It is closer to a form of harmless parasitism, for the ani profits from the activities of the cow without either harming or helping the cow. It also illustrates how sharp birds are—ready to take advantage of any factor in their environment that will help them get their food.
EARLY BIRD LISTING
I wonder how many of the people who go out making lists of spring birds know that bird listing goes back to ancient times. It's a modern sport, but earlier bird watching was serious, and a competitive listing of birds played a part in as important an event as the selection of the site of the city of Rome.
The story, as Plutarch tells it, is that Romulus wanted the city on what became known as Roma Quadrata; Remus wanted it on the Aventine Mount. As was the custom in those days, they concluded at last to decide by a divination from a flight of birds. The twins placed themselves apart at some distance and watched. Remus, they say, saw six vultures, a truly notable flight; Romulus saw twelve and from this rare and unusual occurrence Romulus' choice of the site for the city was accepted.