Egg rejection behavior does not explain the lack of cowbird parasitism on an eastern North American population of Red-winged Blackbirds

Table 3 Cowbird parasitism frequencies on common host species in Berks County, Pennsylvania

Host species	Scientific name	2018 breeding season		Late 19th century^a
Host species	Scientific name	n	% parasitized	n	% parasitized
Willow Flycatcher^b	Empidonax traillii	2	0.0	–	–
Eastern Phoebe	Sayornis phoebe	1	100	unk^c	unk
Red-eyed Vireo^d	Vireo olivaceus	–	–	10	30.0
Wood Thrush	Hylocichla mustelina	13	0.0	31	0.0
American Robin	Turdus migratorius	10	0.0	13	0.0
Gray Catbird	Dumetella carolinensis	19	0.0	45	0.0
Brown Thrasher	Toxostoma rufum	1	0.0	36	0.0
Chipping Sparrow	Spizella passerina	4	25.0	24	41.7
Field Sparrow	Spizella pusilla	3	33.3	33	21.2
Song Sparrow	Melospiza melodia	8	12.5	33	21.2
Eastern Towhee	Pipilo erythrophthalmus	–	–	26	0.0
Yellow Warbler	Setophaga petechia	2	50.0	1	0.0
Northern Cardinal	Cardinalis cardinalis	6	0.0	4	0.0
Indigo Bunting	Passerina cyanea	–	–	29	24.1
Totals		68	7.4	285	11.9

^aData from Levi Mengel egg collection (1884–1900) in the Reading Public Museum (Uhrich 1997)
^bNo nests of the Willow Flycatcher or the very similar Alder Flycatcher were previously reported in Berks County, although birds of both species were observed during the breeding season (Uhrich 1997)
^cTotal number of nests and parasitism frequency unknown but 8 nests recorded as parasitized and this species was noted as a common host
^dSpecies lacking data from the 2018 breeding season (indicated by dashes) were present in our study areas but at a low density and no nests were located

ISSN: 2053-7166