Male Morphology and Nest-site Quality in House Sparrows

-Previous research on House Sparrows (Passer domesticus) in Europe indicated that males with larger bibs are more likely to obtain nest sites with multiple potential nests. To test this observation experimentally, I created nest sites containing either one or two nest boxes. 1 found no morphological differences, including bib size, between males at single-box nest sites (SBNS’s) and those at double-box nest sites (DBNS’s). Pairs in DBNS’s were more likely to renest than pairs in SBNS’s in 1992, leading to increased seasonal reproductive success for pairs at DBNS’s. Although pairs at DBNS’s fledged more young over the season, I could not detect a strong preference for DBNS’s. Pairs in DBNS’s did not begin reproducing prior to those in SBNS’s, as might be expected if birds preferentially occupied DBNS’s prior to SBNS’s. More DBNS’s than SBNS’s were occupied in 1991, but this was not true in 1992 when sample sizes were larger. Received 2 Dec. 1996, Accepted I1 May 1997. Multiple nest sites on a territory may be beneficial, possibly allowing pairs to choose the best site for nesting, to renest in a clean site free of ectoparasites, or to reduce the interval between broods (Moller 1993, Meek and Robertson 1994). Experimental manipulation of the number of nest boxes on a territory indicates that Eastern Bluebirds (Sialia sialis) are more likely to occupy or respond from territories with multiple nest boxes (Meek and Robertson 1994, Plissner and Gowaty 1995). If multiple nest sites are beneficial, then dominant or high quality males should be more likely to occupy territories with multiple cavities than will subordinate or low quality males, and females should prefer to nest with males holding territories with multiple cavities. House Sparrows are facultative cavity nesters and will utilize nest boxes, as well as construct open nests. Cavity nest sites are preferred to sites with no cavities (Cink 1976, Moller 1988). Pairs that nest in cavities or nest boxes have greater reproductive success (Cink 1976, McGillivray 1981), in part because these nests are less likely to be destroyed during storms (Moller 1988). In Europe, bib size is under sexual selection, with large-bibbed males being dominant (Moller 1987a, b), being preferred by females (Moller 1988) and having greater reproductive success (Moller 1988). Large-bibbed males are more likely to obtain nest sites with multiple cavities (Moller 1988), and males with experimentally enlarged bibs occupied nest sites with more nest boxes than did control males (Veiga 1993). House Sparrows may switch nest boxes between nesting attempts I Dept. of Biology, The Univ. of New Mexico, Albuquerque, New Mexico 87131