ABSTRACT

1. THE OCCURRENCE OF BREEDING SONGBIRDS: USING DATA FROM THE SURVEY, MONITORING AVIAN PRODUCTIVITY AND SURVIVORSHIP (MAPS) TO TEST HYPOTHESES ABOUT VEGETATION AND EDGE EFFECTS Species (n) VEGETATION DISTANCE FROM FOREST EDGE (m) Field Open Canopy Abundant Shrubs Open Canopy Closed Canopy 10-40 40-110 110-200 200-255 Closed Canopy Few Shrubs Black and White Warbler 1.5 1.14 1 2 1 1.83 Blue-winged Warbler 0.4 0.43 0 0 0.6 0.67 Carolina Wren 0.6 0.14 0 1.67 0.4 0 Mist-Nets Eastern Towhee 0.6 0.43 1 1.67 0.2 0.67 Eastern Tufted Titmouse 0.3 0.86 1 3.67 0.8 0.33 Eastern Wood Peewee 0.6 0.86 1 0.33 0.4 1 Gray Catbird 1 0.57 0.67 1 0.8 0.83 Hooded Warbler 4.7 0.86 1 5 1.6 4.5 Northern Cardinal 0.4 1.6 2.3 0.67 0.8 0.33 Ovenbird 5.9 4.4 5.3 4.7 3.8 6.2 Ruby-throated Hummingbird 0.7 0.14 0.33 1 0.2 0.5 White-eyed Vireo 1.9 0.14 0.33 1 1 3 Wood Thrush 1.3 6.4 9.3 1 7 1 Worm-eating Warbler 1.7 1 1.33 1.33 0.8 1.83 Kristen Boccumini, The Richard Stockton College of New Jersey, Pomona, NJLinda Smith, The Richard Stockton College of New Jersey, Pomona, NJ Tedor Whitman, The Wetlands Institute, Stone Harbor, NJ Laura Thompson, Valparaiso University, Valparaiso, IA Rachel Wilson, Bryn Mawr College, Bryn Mawr, PA ABSTRACT MAPS is a standardized survey of breeding songbirds in the woodlands of North America by capturing birds in mist nets. Belle Plain State Forest in the coastal pinelands of southern New Jersey is one of many sites in which this annual survey is performed. We used four years of survey data (1999-2002) on the presence of songbird species at this site to examine the influence of vegetation and edge on the occurrence of songbird species. The study area borders a field and has two distinct vegetation types; one with an open canopy and ground cover and another with a closed canopy and little ground cover. We examined where species were captured regarding vegetation type and distance from edge. Our analyses show that certain species were captured significantly more often in one of the two vegetation types as well as certain distances from the forest edge. We suggest that our results can be used for forest management decisions in the NJ pinelands, an area with increased habitat fragmentation due to increasing development. In addition, we propose that our technique of using existing data to test hypotheses about songbird conservation has wide spread application. The study that we initiated in the season of 2002 was part of a student project in an NSF funded REU summer program, the Coastal Conservation Research Project. We characterized the vegetation types and measured the distance of each net to the forest edge so that we could test our hypotheses about how these variables should influence where we frequently caught certain species in the forest. The frequency in the number of birds caught per species was calculated on the total songbird count per net (total # birds in species/total # in species caught in net). Discussion In our avian study, utilization of long-term census data from MAPS revealed significant impacts of landscape heterogeneity on mist- netted songbird species in the area. Microhabitat effects may influence survey findings in the MAPS study, especially since forest degradation can affect natality and fatality in animal populations (Cooper & Walters, 2002). At our BellePlain State Forest MAPS site, vegetation and distance from forest edge influenced bird prevalence within the forest. Our findings are further supported by how the occurrence of songbirds in relation to edge and vegetation coincides with their natural history. For instance, in Figure 1, it is known that Blue-winged Warblers prefer shrubby areas for breeding while Hooded Warblers prefer mature forests in which males sing and females nest. Figure 2 shows how the Ovenbird,a frequent species in the coastal pineland forests, is a generalist,whereas the Wood Thrush feeds in moist, leafy areas and prefers dense vegetation to conceal and shade nests. The Northern Cardinal is typically known as an edge species preferring brushy areas and clearings while the White-eyed Vireo prefers a contrasting habitat and is typically found in dense shrubbery and secondary growth (Figure 3). Of the two factors we studied, vegetation type seems a stronger factor than edge. The use of nation-wide long-term census data such as MAPS can enable researchers to further understand causes for changes in populations and ultimately biodiversity. Trends discovered from such nation-wide research can direct effective management decisions enhancing the conservation of organisms. Blue-winged Warbler Map of Belle Plain State Forest MAPS Site Hooded Warbler INTRODUCTION Fragmentation is known to affect animal populations due to various factors such as edge effects, size and isolation of fragments, and habitat degradation (Beir & Noss, 1998; Smith & Hellman, 2002). An ideal way to examine how such factors influence animal populations is to utilize long term census data from standardized surveys. MAPS, developed in 1989 by the Institute for Bird Populations, is an annual census of breeding songbirds at over 500 sites in North America. Birds are known to be influenced by habitat disturbance (Askins, 2000; Brawn, Robinson, & Thompson III). Each site used in MAPS is likely to exhibit different characteristics related to fragmentation as for instance distance to forest edge or vegetation type. In our study, we tested the hypotheses that the abundance and diversity of avian species would be influenced by the distance to the forest edge and vegetation type. We used four years of census data from a MAPS site in the coastal plains of southern New Jersey. We suggest that this use of an established census program to address conservation questions is useful for making local as well as broad scale conservation decisions. RESULTS Certain songbirds showed preferences for forest edge over forest interior and/or vegetation type, while others exhibited no preference. We used songbird species that were caught at least seven times during the four breeding seasons (ranging from 7 to 102). Table 1 shows our calculations for each of 14 species and displays a comparison of their preferences for vegetation type and distance from the forest edge. Figure 1 compares the Blue-winged Warbler (Vermivora pinus), favorable to the forest interior, and the Hooded Warbler (Wilsonia citrina), preferring closed canopy vegetation. Figure 2 compares the Ovenbird (Seiurus aurocapillus), showing no location preference, and Wood Thrush (Hylocichla mustelina), desiring closed canopy with varied distance from forest edge. Figure 3 compares the Northern Cardinal (Cardinalis cardinalis), preferring edge areas of the forest, and White-eyed Vireo (Vireo griseus), desiring open canopy in the forest interior. Ovenbird Wood Thrush Literature Cited Brawn, Robinson, & Thompson III. 2001. “The Role of Disturbance in the Ecology and Conservation of Birds” Annual Review of Ecological Systems. 32; 251-276. Cooper & Walters. 2002. “Experimental Evidence of Disrupted Dispersal Causing Decline of an Australian Passerine in Fragmented Habitat” Conservation Biology. 16:2; 471-478. Smith & Hellman. 2002. “Population Persistence in Fragmented Landscapes” Trends in Ecology and Evolution. 17:9; 397-399. MATERIALS AND METHODS Our study site is located within the coastal plains of southern New Jersey in Belleplain State Forest and is mainly a pine/oak forest. The MAPS census of North America established a standardized protocol that is to be followed at all study locations. At our study site we set-up 19 mist nets and monitored these nets one day per week from 5:00-12:00 during 10 weeks of the songbird breeding period from mid- May to late July 2002. Birds caught in mist nets were banded, weighed, and measured. This study was done on the same site for the breeding seasons of 1999-2002. We used Global Positioning Systems (GPS) to measure the distance of each net from the edge between the forest and an opening of old field growth (see map). In addition, in the area of the forest in which our nets were positioned there were two very distinct vegetation types. One type consisted of a closed canopy with a high percentage of open forest floor and exposed leaf litter. The other vegetation type consisted of a canopy in which there were many gaps and an extensive shrub layer especially laurel and blueberry/huckleberry. Table 1. The species that were caught in mist nets 7 or more times in each of four consecutive breeding seasons from 1999-2002. The average number of individuals per net are listed for both vegetation type and distance from the forest edge. Northern Cardinal Acknowledgments ~ The Coastal Conservation Research Program NSF Research Experience for Undergraduates ~ The Wetlands Institute ~ The Richard Stockton College of New Jersey. White-eyed Vireo