Academic journal article The American Midland Naturalist

Veery Nest Sites in a Mid-Atlantic Piedmont Forest: Vegetative Physiognomy and Use of Alien Shrubs

Academic journal article The American Midland Naturalist

Veery Nest Sites in a Mid-Atlantic Piedmont Forest: Vegetative Physiognomy and Use of Alien Shrubs

Article excerpt

ABSTRACT.-Veery (Catharus fuscescens) nest sites were compared to unused sites in a Middle-Atlantic Piedmont forest to determine if nest placement was random or biased with respect to forest structure and alien vegetation. Thus far, available data shows alien plants have a detrimental or neutral effect on the ecology of forest birds; however, empirical data regarding the proximate influence of invasive alien shrubs on avian nest placement in North American forests is lacking. Nest sites were distributed non-randomly in relation to vegetation density and were characterized by dense foliage below 1.5 m with sparse overstory at 2.5 to 3 m. Sites occurred within moist forest in floodplains and on south- and east-facing slopes. All nest sites contained alien shrubs, and alien vegetation supported 84% of nests. Shrub diversity did not differ between nest sites and unused sites yet more alien shrub species were found at nest sites. The density of native shrub-layer foliage did not differ between the two treatments; however, the density of alien shrub foliage was greater at nest sites. In this forest there was no relationship between the density of alien vegetation and the density of native vegetation. These data suggest that alien shrubs have replaced native shrub species and exerted a largely additive effect on foliage density providing the proximate cues for nest placement. The high success rate (70%) of nests within sites used in analyses suggests that the alien shrubs providing these cues are not substantially elevating nest failure rates. Thus, some temperatebreeding Neotropical forest-interior birds may react positively to a change in forest structure resulting from the invasion of alien shrubs. Ecological release resulting from the increase in available nest sites created by alien shrubs may explain the recent regional spread of the Veery. Region-specific studies are needed to determine the forest breeding birds that are affected, either positively or negatively, by the altered spatial heterogeneity created by alien shrubs.

INTRODUCTION

Many investigators have shown that the vegetation used by forest birds as nest sites may differ significantly from that of surrounding vegetation (e.g., Martin and Roper, 1988; Sakai and Noon, 1991; Steele, 1993; Matsuoka et al., 1997). Because the vulnerability of a nest to predators and brood parasites may depend on surrounding vegetative physiognomy, natural selection should favor individuals that choose nest sites with vegetative characteristics that maximize productivity (Martin, 1988; Martin and Roper, 1988). These characteristics may provide an important cue in the assessment of habitat at larger spatial scales: forest patches with multiple nest sites may ensure against nest failure and dilute predation pressure (Martin, 1992; Jones and Robertson, 2001). Thus, the environmental variables that differ significantly between a group of nest sites and their associated random sites might reveal those characteristics that stimulate nest placement and positively influence fitness. Several studies concur with this assertion (e.g., Martin and Roper, 1988; Kelly, 1993; Wilson and Cooper, 1998).

The Veery (Catharus fuscescens) is a declining, area-sensitive, forest-dependent, low shrub or ground-nesting thrush that has recently warranted international conservation attention (Saner and Droege, 1992; Herkert, 1995; Moskoff, 1995; Sauer et al., 2001; Remsen, 2001). This thrush typically occurs in younger and denser forest than sympatric congeners (Moskoff, 1995). Few studies have focused specifically on the habitat use of the Veery and none have investigated nest site use. However, many authors have reported the Veery to be associated with dense broadleaf vegetation often within riparian areas (Moskoff, 1995).

Prior to 1942 the Veery was an extremely rare breeder on the Middle-Atlantic Piedmont Physiographic Province of the District of Columbia, Maryland, Delaware, Pennsylvania and central New Jersey; only 19 breeding-season records are available from this province prior to 1942 (Heckscher, 2002). …

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