Natural Resources, School of


Document Type


Date of this Version



Ecology, 67(5), 1986, pp. 1206-1218


Copyright 1986 by the Ecological Society of America. Used by permission.


Colonially nesting Cliff Swallows (Passeriformes: Hirundo pyrrhonota) in southwestern
Nebraska, USA, are commonly parasitized by hematophagous swallow bugs (Hemiptera: Cimicidae:
Oeciacus vicarius) and fleas (Siphonaptera: Ceratophyllidae: Ceratophyllus celsus). We examined to
what degree these ectoparasites represent a cost of coloniality for Cliff Swallows. The number of
swallow bugs per nest increased significantly with Cliff Swallow colony size. Body mass of nestling
swallows at 10 d of age declined significantly as the number of bugs per nestling increased. By fumigating
half of the nests in some colonies, killing the bugs, and leaving half of the nests as nonfumigated
controls, we showed that swallow bugs lower nestling body mass and nestling survivorship in large
Cliff Swallow colonies but not in small ones. Bugs cost nestlings, on average, up to 3.4 g in body mass,
and reduced survivorship by up to 50%. Parasitism by fleas showed no consistent relationship with
colony size during the nestling period but increased significantly with colony size early in the season,
when birds were first arriving in the study area. Fleas did not affect nestling body mass or survivorship
and thus, unlike swallow bugs, are probably not important costs of coloniality to Cliff Swallows. Field
observations and nest fumigation experiments showed that Cliff Swallows apparently assess which
nests are heavily infested with swallow bugs early each spring and select parasite-free nests, leading
sometimes to alternate-year colony site usage. Cliff Swallows were more likely to construct new nests
(rather than reusing old ones) in large colonies than in small colonies, probably in response to heavier
infestations of ectoparasites in the existing nests of large colonies.