Nest-Site Characteristics and Nest Predation in Harris' Sparrows and White-Crowned Sparrows in the Northwest Territories, Canada

Abstract

ABssAcr.-I examined the relationship of nest-site and nest-patch characteristics to nest success in ground-nesting Harris' Sparrows (Zonotrichia querula) and Gambel's White-crowned Sparrows (Z. leucophrys gambelii) in the forest-tundra ecotone of the Northwest Territories, Canada. I found 34% of all Harris' Sparrow nests depredated, primarily by arctic ground squirrels (Spermophilus parryii), while no White-crowned Sparrow nests were disturbed by predators. White-crowned Sparrow nests appeared to be less susceptible to predation than Harris' Sparrow nests because the former were placed in areas with more shrubs and ground cover, and denser vegetation, than were Harris' Sparrow nests. Comparison of successful and depredated Harris' Sparrow nests supported the idea that interspecific differences in rates of nest predation were due to differences in concealment rather than to density-dependent nest predation. Successful Harris' Sparrow nests were placed in areas with more shrub cover and more dense vegetation within 5 m of the nest than were depredated nests. Orientation of the nest entrance did not differ between Harris' and White-crowned sparrow nests, nor between successful and depredated Harris' Sparrow nests. However, nest entrances of both species were nonrandomly oriented, with mean orientation vectors 1350 to 170? from prevailing storms. Reasons for the tendency of Harris' Sparrows to select sites where chances of predation are relatively high are unclear, but could be related to a lack of suitable nest sites in the study area.

Distribution, Abundance, and Habitat Characteristics of the Buff-Breasted Flycatcher in Arizona

“…Many researchers have noted relationships between vegetation structure and/or floristics and nest site selection by forest-dwelling passerine birds (Martin and Roper 1988;Sakai and Noon 1991;Knopf and Sedgewick 1992;Kelly 1993;Norment 1993). The influence of vegetative characteristics on nest site selection 15 may be exerted on several scales.…”

“…Several factors may affect selection of a nest site or patch characterized by particular vegetative structure or floristics. Martin and Roper (1988) and Norment (1993) found that nest placement by hermit thrushes (Catharus guttatus) within a plant and within a patch affected probabili^ of nest predation. In both studies, nests placed in denser vegetation were less likely to be depredated.…”

Nest orientation of the Spotted Barbtail, Premnoplex brunnescens, is strongly correlated with stream flow

“…Recently, nest orientation has also been shown to vary intraspecifically, in a predictable manner, with latitude (Burton 2007). Most species, however, show a preference for one direction, generally that which exposes them to, or protects them from, wind and solar radiation (Ardia et al 2006;Burton 2006;Facemire et al 1990;Mezquida 2004;Norment 1993). The barbtails studied here nest in a cool, dark, humid environment, and rear their young in thick, enclosed nests with a downward-opening entrance tube (Greeney 2008a(Greeney , 2008b.…”

“…A wide variety of both circular and linear statistics have been used in previous studies of nest orientation (e.g., Ardia et al 2006;Austin 1974;Burger and Gochfeld 2005;Norment 1993;Ricklefs and Hainsworth 1969). As circular distributions do not usually conform to the assumptions of many of these tests (Cain 1989;Zar 1999), most recent studies of circular data rely on one of several analyses.…”

“…While some studies reveal little or no pattern of nest orientation (e.g., Albano 1992;Rendell and Robertson 1994;Tarvin and Smith 1995), many groups, representing a variety of nest architectures, do show strong preferences in the orientation of their nests (Austin 1974;Balgooyen 1990;Bergin 1991;Hooge et al 1999; Martin and Roper 1988;Mezquida 2004;Nores and Nores 1994;Walsberg 1981). Typically, nest orientation has been found to be correlated with either prevailing winds (Facemire et al 1990;Mezquida 2004;Norment 1993) or sun exposure (Burton 2006;Hartman and Oring 2003;With and Webb 1993;Yanes et al 1996), both of which may have a direct effect on the microclimate of the nest (Ardia et al 2006;Hartman and Oring 2003). Thus, nest orientation and placement are important aspects of avian reproduction and may affect embryonic development, hatching success, and nestling growth (Austin 1974;Burton 2006;Cook et al 2003;Lloyd and Martin 2004;Viñuela and Sunyer 1992), the energetics of attending adults (Vleck 1981;White and Kinney 1974), and overall nesting success (Filliater et al 1994;Martin and Roper 1988;Rauter et al 2002).…”