Breeding Behavior and Reproductive Success of Chipping Sparrows in Northwestern Minnesota

The reproductive biology of Chipping Sparrows (Spizella passerina) was studied during 2 breeding seasons at the University of Minnesota Forestry and Biology Station, Itasca State Park, Minnesota. Reproductive success was determined primarily by the incidence of nest predation. Parasitism by Brown-headed Cowbirds (Molothrus ater) caused a comparatively smaller loss in reproductive success. Four pairs raised two broods in one season. Males assumed nearly all care of first brood fledglings, freeing the female to build a second nest. This strategy of parental care may improve the chances of a pair having a second brood. Pair relationships were typically monogamous. One of 32 males was polygynous. Increased male singing during the first half of incubation appeared to be advertisement for second mates. Males increased the opportunity for additional copulations by visiting other territories containing receptive females. One male obtained a copulation in this manner. Chipping Sparrows showed considerable flexibility in their use of space. Males with older fledglings commonly foraged outside the territory. This may have lowered competition for food between first and second broods, or allowed foraging in areas with higher concentrations of food. Territorial defense was highest during pair formation, largely because of frequent use of areas near territorial borders by pairing adults. Territories shifted frequently after nest predation. Changes in territory location after nest predation may have improved renest success by avoidance of the previous predator