Eastern Kingbird

Tyrannus tyrannus (Linnaeus)

An uncommonly reported host choice, the eastern kingbird was known earlier (Friedmann, 1963:49) to have been parasitized only from some 15 records. To these we may now add 9 more: 2 from Illinois (Graber, Graber, and Kirk, 1974:8); 4 from Ontario (Ontario nest records files, out of 716 nests reported); I from North Dakota (R. E. Stewart); 1 from Maryland (Delaware Museum of Natural History); and 1 from Cincinnatus, New York (Western Foundation). One of the Illinois records is of a nest containing a large young cowbird which “probably” fledged.

In attempting to evaluate this increase in the number of instances of parasitism on this flycatcher, we must take into consideration the fact that one of us (S.I.R.) has found the eastern kingbird to be a rejecter species. Experiments at each of 33 nests resulted in ejection of an artificial or real cowbird egg. These experiments involved samples of the kingbird population in Connecticut, Maryland, Michigan, and Manitoba. Because ejection of the alien egg is the typical response, it follows that much of the parasitism that may be perpetrated on this species would go undetected. This makes it all the more remarkable that there should be as many as 5 additional observed records since the 1963 compilation; this can only mean that the eastern kingbird is victimized somewhat frequently.

The Illinois instance (above) of a well-developed young cowbird in a kingbird's nest suggests that the host's usual rejection reaction is to the newly laid cowbird egg, and that if it is not then ejected, the kingbird will tolerate and incubate it, and rear the young parasite. Whether, in this particular instance, there was some physical or other obstacle to removal of the egg is not known.

WESTERN KINGBIRD