The term brood-parasitic intruder is used to describe a bird that searches for and lays eggs in a nest built by a bird of another species. For example, the brown-headed cowbird is known to be a brood parasite of the smaller willow flycatcher. Ornithologists theorize that those flycatchers which recognize, but do not vocally react to, cowbird calls are more apt to defend their nests and less likely to be found and parasitized. In a study published in

The Condor (May 1995), each of 13 active flycatcher nests was categorized as parasitized (if at least one cowbird egg was present) or nonparasitized. Cowbird songs were taped and played back while the flycatcher pairs were sitting in the nest prior to incubation. The vocalization rate (number of calls per minute) of each flycatcher pair was recorded. The data for the two groups of flycatchers are given in the table and saved in the COWBIRD file. Do the data suggest (at

a = .05) that the vocalization rates of parasitized flycatchers are higher than those of nonparasitized flycatchers?

Parasitized Not Parasitized

2.00..... 1.00

1.25..... 1.00

8.50 ..... 0

1.10 ..... 3.25

1.25 ..... 1.00

3.75 ...... 25

5.50