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Habitat Associations of Grasshopper Sparrows in Southern Québec
Benoît Jobin and Gilles Falardeau

Northeastern Naturalist, Volume 17, Issue 1 (2010): 135–146

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2010 NORTHEASTERN NATURALIST 17(1):135–146 Habitat Associations of Grasshopper Sparrows in Southern Québec Benoît Jobin1,* and Gilles Falardeau1 Abstract - Ammodramus savannarum (Grasshopper Sparrow) is a grassland passerine considered at risk in several regions of eastern USA and Canada. Detailed information is lacking on structure and breeding-habitat components for Grasshopper Sparrows in eastern Canada. We surveyed Grasshopper Sparrows in suitable habitats in southwestern Québec and described habitat characteristics to increase our knowledge of the species’ breeding-habitat associations in eastern Canada. Grasshopper Sparrows were detected in grass-dominated abandoned fields, pastureland, and hayfields generally located on poor sandy soil supporting low and sparse vegetation. Suitable sites with or without Grasshopper Sparrows did not differ in their structural components nor in their plant composition. Sites used by Grasshopper Sparrows were embedded within a perennial crop-dominated matrix where forest cover was reduced, and were larger than sites where they were absent. Conservation and stewardship activities should aim to secure large tracts of grasslands in southwestern Québec. Introduction Ammodramus savannarum Gmelin (Grasshopper Sparrow) is a small grassland bird that occurs mainly in central and eastern United States and southern Canada, where it reaches its northern limits (Vickery 1996). It generally inhabits well-drained grasslands with scattered perch sites (e.g., low shrubs, fenceposts, robust perennial plants) and may be found in a range of grasslands with similar habitat structure including old fields, pastureland, and hayfields (Earley 2007, Hainault 1996, Speirs and Orenstein 1967, Vickery 1996). This species is restricted to specific habitats and is relatively uncommon throughout parts of its range, especially in the east. Grasshopper Sparrows have declined in eastern Canada and elsewhere in eastern North America (Askins 1993; Herkert 1994, 1995). The North American Breeding Bird Survey (BBS) (Sauer et al. 2008) indicates a significant population decline in the United States (-3.6%/year) and Canada (-6.0%) between 1966 and 2007; this decline was well detected in the northeastern states of the USA (USFWS Northeast Region no. 5; -5.4%) and in Ontario (-4.1%) (data are too scarce for a reliable trend estimate for Québec). Grassland habitat loss and fragmentation due to intensification of agriculture, conversion to row crops and conifer tree plantations, and land abandonment are likely responsible for the decline of this species (Brennan and 1Canadian Wildlife Service, Environment Canada, 1141 Route de l’Église, PO Box 10100, Québec, QC, G1V 4H5, Canada. *Corresponding author - benoit.jobin@ec.gc.ca. 136 Northeastern Naturalist Vol. 17, No. 1 Kuvlesky 2005, Sauer et al. 2008). The Grasshopper Sparrow is recognized as a species of moderate concern in the Lower Great Lakes/St. Lawrence Plain Bird Conservation Region (Hartley 2007), and the subspecies A. s. pratensis Vieillot, which occurs in the northeastern part of its range, is now listed as endangered, threatened, or of special concerns in several states and provinces (Vickery 1996). It is listed as a species likely to be designated as threatened or vulnerable in Québec and is now mostly restricted to the Pontiac region west of the Ottawa–Gatineau metro region (Jobin and Falardeau 2005), where beef cattle production and large extents of grassland still prevail (Jobin 2003, Jobin et al. 2005). Information on structure and breeding-habitat components used by Grasshopper Sparrows is scarce in eastern Canada, and no quantitative study has ever been conducted in Québec. Our objectives were to: 1) locate active breeding sites in the Pontiac region of southwestern Québec, and 2) gather detailed information on habitat use. This information will increase our knowledge of Grasshopper Sparrow breeding-habitat associations in eastern Canada and aid in identifying suitable habitats for further survey efforts, locate additional breeding sites, and guide conservation and habitatmanagement actions. Methods This study was conducted in the Pontiac region (≈1250 km2), QC, Canada, west of the Ottawa–Gatineau metro region and north of the Ottawa River, from Chichester (45°55'N, 77°07'W) to Quyon (45°31'N, 76°14'W). This agroforested landscape is composed of pastureland and hayfields, with scattered row cropfields (corn, soybean). It differs from other regions of the St. Lawrence Lowlands ecoregion, where the landscape is highly dominated by intensive row-crop agriculture. The Pontiac region now holds the only large stable population of Grasshopper Sparrows in Québec (Hainault 1996, Jobin and Falardeau 2005). Similar to Jobin (2003), we located suitable breeding sites by driving along roads in May 2004 and plotting on 1:50,000 topographic maps habitats deemed suitable, including previously known breeding locations. We identified suitable habitats as grasslands showing key habitat features known to be used by Grasshopper Sparrows (dry open fields with sparse vegetation and scattered perch sites, such as shrubs and Verbascum thapsus L. [Common Mullein] stalks; Vickery 1996), and we discarded as unsuitable habitat row-crop fields, old fields with high shrub cover, and high-quality forage crops such as dense hayfields or seeded pastures lacking numerous perch sites because of recurrent mowing or intensive grazing. Grasslands <5 ha holding suitable habitat structure were also discarded because this species is generally considered area-sensitive (Davis 2004, Johnson and Igl 2001) and because the minimum habitat patch size from Jobin’s (2003) land-cover map was 5 ha. 2010 B. Jobin and G. Falardeau 137 Overall, 32 sites with suitable habitat and where landowner permission was granted were surveyed. Bird surveys were conducted twice in each site in 2004 (3–6 and 17–23 June) and 2005 (6–9 and 20–21 June) from sunrise to 1000 under clement weather conditions (no heavy rain or extreme heat, wind speed under 20 km/hr). A single surveyor entirely covered suitable habitats by walking slowly within each site along parallel transects approximately 100 m apart and eliciting territorial bird response by broadcasting the two song types of the Grasshopper Sparrow at regular intervals (≈100 m). We used the playback method and conducted surveys along transects instead of using point counts, because our objective was to detect the maximum number of sparrows in each field. Songs were broadcast using an MP3 player (Egoman Technology Corp.) and hand-held speakers (Sony SRS-T57). Each responding individual was recorded on a map of the survey site at each visit. Singing birds were recorded as males, non-singing birds were recorded as unknown gender because males and females are similar. The maximum number of males detected at any given survey was corrected with site area as an index of bird density (number of males/ha). Vegetation surveys were conducted 14–18 July 2004 by placing circular quadrats (88 cm in diameter) in a systematic manner throughout fields that had been surveyed for Grasshopper Sparrows. Quadrats were spaced >50 m apart along the bird-survey transects, and a minimum of 10 quadrats were surveyed in each site; the number of quadrats varied by site (mean = 14; range = 11–29). Cover (%) of live and dead vegetation, bare soil, rocks, lichens, and moss was visually estimated in each quadrat along with height (cm) of live and dead vegetation and litter depth. We counted the number of plant stems and leaves touching a vertical rod at 25-cm height intervals placed in the center of the quadrat (Davis 2004, Sutter and Brigham 1998) and the sum of all hits at all height intervals was used as a measure of vegetation density (Dieni and Jones 2003, Whitmore 1981). Average values of descriptive variables measured in quadrats were calculated for each site, and the coefficient of variation was calculated as a measure of structural heterogeneity (Bollinger 1995, Sutter and Brigham 1998). Dominant and subdominant (cover >5%) plant species were noted in each quadrat along with their relative cover. We also estimated the number of shrubs and mullein stalks as an index of perch density (number/ha) at each site, and the presence of habitat features likely to affect habitat use by Grasshopper Sparrows (hedgerows, shrub stands, wetlands, isolated trees, lichen, exposed sand deposits) were noted. We calculated the relative land cover of annual crops, perennial crops (including hayfields, pastureland, and old fields), forest, urban areas, and open water/wetlands in a 200-m buffer surrounding each site to evaluate the effect of landscape-scale habitat components on Grasshopper Sparrow habitat use. This information was extracted from the land-cover map of Jobin (2003) produced in 2000. Numbers of land-cover patches along with 138 Northeastern Naturalist Vol. 17, No. 1 Shannon-Wiener and evenness indices were also calculated to characterize the surrounding landscape heterogeneity. Out of the 32 surveyed sites, 5 were discarded from the analyses because 4 had been ploughed prior to the 2005 field season and one site was mowed prior to the vegetation survey. In addition, landscape buffers overlapped for two pairs and two trios of sites (range = 16–62%; McMaster et al. 2005) because some sites were only separated by roads or hedgerows (mean nearest-neighbour distance = 2960 m; range = 300 to 12,500 m). Because these sites were not statistically independent, we randomly selected one site from each pair or trio with overlapping buffers, and therefore discarded 6 additional sites. Bird-habitat relationships were thus analyzed for 21 sites. We used non-parametric Wilcoxon tests to compare mean values of descriptive quantitative variables between sites with and without Grasshopper Sparrows, and contingency table analyses (Fisher's exact 2-tailed test) for dichotomous variables. Spearman correlation (rs) and Wilcoxon tests were also used to relate bird density to descriptive variables. We did not use logistic or multiple regressions due to low sample size. A non-metric multidimensional scaling analysis (NMDS) was performed on landscape buffer values to visualize groupings of sites (n = 21) in a two-dimensional space. NMDS is an ordination method that maximizes rank-order correlation between distance measures and distance in ordination space, and was preferred to principal component analysis because descriptive variables were not normally distributed and showed no linear relationships (Jongman et al. 1995, McCune and Grace 2002, Minchin 1987). We used the Sørenson (Bray-Curtis) distance measure on relativized variables and the autopilot “slow and thorough” procedure in PC-ORD V.4 (McCune and Mefford 1999) with an automatically generated file from preliminary analysis of the NMDS as the starting configuration, following McCune and Grace (2002). We calculated Spearman correlation coefficients between variables and site scores along the first and second axes to identify variables driving the ordination. Detrended correspondence analyses (DCA) were used to evaluate similarities of study sites with respect to plant composition based on frequency of occurrence and mean cover of each species within each field using the number of quadrats as the sampling base. Distinct analyses were performed using all plant species (46 species) and a subset of plant species (31 species) discarding those only observed at one site. Mean site scores along the first two axes were compared between sites with and without Grasshopper Sparrows using non-parametric Wilcoxon tests. Ordination and statistical analyses were performed with PC-ORD V.4 (McCune and Mefford 1999) and JMP V 3.1 (SAS Institute, Inc. 1995). Statistical significance was set at α = 0.05. Results Grasshopper Sparrows were detected at 13 of the 21 study sites, among which were 10 sites where males were detected both years. Sites 2010 B. Jobin and G. Falardeau 139 used by Grasshopper Sparrows ranged between 6.4 and 37.1 ha in size and were all grasslands, ranging from young abandoned fields located on poor sandy soil to regularly mowed hayfields lacking prominent perch sites. Sites generally presented the same facies of being poor grasslands where the vegetation was sparse and short. Mean live and dead vegetation covered 47 and 33% of quadrats, respectively, whereas bare soil covered approximately 19%. Mean vegetation height was 23 cm, and litter depth was less than 4 cm. Sites where sparrows were detected were twice as large compared to those where they were absent (Table 1). There was no difference in mean values of vegetation characteristics, structural heterogeneity, and perch-site density (number of mullein stalks and shrubs per ha) between the two groups of sites. Large shrub thickets, hedgerows, isolated trees, wetland, lichen, and sand deposits were rarely present at study sites, and the proportion of sites where their presence was recorded did not differ between sites with and without sparrows (all P > 0.11; Fisher’s test). Land cover surrounding study grasslands in a 200-m radius influenced Grasshopper Sparrow use as there were more perennial crops (grassland, Table 1. Habitat variables (mean and SD) at sites with and without Grasshopper Sparrows in the Pontiac region, QC, Canada, 2004. χ2 = Wilcoxon test, chi-square approximation. With sparrows Without sparrows (n = 13) (n = 8) Wilcoxon test Habitat variable Mean SD Mean SD χ2 P Structure Site area (ha) 15.86 8.32 7.42 2.40 7.57 <0.01 Mullein density (n/ha) 9.25 18.22 9.76 12.23 0.11 0.74 Shrub density (n/ha) 7.44 8.89 3.68 4.40 0.78 0.38 Vegetation Cover of live vegetation (%) 45.63 10.11 49.10 15.05 0.13 0.72 CV of cover of live vegetation 0.35 0.08 0.33 0.09 0.64 0.42 Cover of dead vegetation (%) 35.80 10.13 28.19 13.04 1.89 0.17 CV of cover of dead vegetation 0.45 0.16 0.55 0.18 1.52 0.22 Cover of bare soil (%) 17.30 5.28 22.72 9.41 1.52 0.22 CV of cover of bare soil 0.62 0.22 0.63 0.11 0.13 0.72 Number of plant hits 2.65 1.04 2.38 1.30 0.82 0.37 CV of number of plant hits 0.62 0.17 0.65 0.20 0.16 0.69 Mean vegetation height (cm) 23.90 7.80 20.84 6.50 0.69 0.40 CV of mean vegetation height 0.39 0.13 0.39 0.09 0.16 0.69 Litter depth (cm) 3.59 1.70 2.90 1.98 0.76 0.38 CV of litter depth 1.07 0.71 1.21 0.52 0.89 0.35 Landscape buffer (200m) Annual crops (%) 5.70 10.04 3.57 8.84 0.83 0.36 Perennial crops (%) 59.08 18.49 42.54 19.37 3.82 0.05 Forest (%) 31.82 20.47 50.50 16.02 4.11 0.04 Open water/Wetlands (%) 1.55 3.15 1.78 3.31 0.04 0.85 Urban (%) 0.46 1.66 0.27 0.75 0.08 0.78 Number of patches 10.62 9.75 13.38 12.20 0.90 0.34 Shannon-Wiener index 0.73 0.21 0.76 0.19 0.13 0.72 Evenness index 0.79 0.20 0.83 0.12 0.02 0.88 140 Northeastern Naturalist Vol. 17, No. 1 pastureland, old fields) and less forest around sites with sparrows than around sites without sparrows (Table 1). Six axes were identified in preliminary analysis of the NMDS, but two were kept (final stress = 8.1), which explained 91% and 5% of the variance, respectively. Sites with sparrows were aggregated on the left side of the first axis on the ordination plot resulting from the NMDS (Wilcoxon test, axis 1: χ2 = 4.72, P = 0.0298; Fig. 1), coverage of perennial crop (-) and forest (+) being most responsible for site positioning along this axis (Table 2). Mean site scores did not differ along the second axis (χ2 = 0.13, P = 0.7173). Site use by Grasshopper Sparrows was not related to the number of land patches and diversity of the surrounding landscape (Table 1). Site area was not correlated with the coverage of any land-cover class in the 200-m radius around sites (all P > 0.10; Spearman correlation). Figure 1. First two axes of a n o n - m e t r i c multidimensional scaling analysis of 5 habitat cover in the 200-m buffer around study sites with (n = 13) and without (n = 8) Grasshopper Sparrows in the Pontiac region, QC, Canada 2004. Axes 1 and 2 explain 91% and 5% of the variance, respectively. Table 2. Spearman correlation coefficients (rs) between habitat cover in the 200-m buffer around study sites and their respective scores on the first and second axis of a non-metric multidimensional scaling analysis. Spearman rs Habitat variable Axis 1 Axis 2 Annual crops (%) -0.18 0.13 Perennial crops (%) -0.95** -0.68* Forest (%) 0.92** 0.65* Open water/Wetlands (%) -0.08 -0.36 Urban (%) -0.06 -0.30 *P < 0.005; **P < 0.0001 2010 B. Jobin and G. Falardeau 141 The maximum number of males detected at a single visit ranged between one and seven, and there was a strong correlation in the maximum number of males detected within a site between years (rs = 0.86, P < 0.0001, n = 21). Male density ranged between 0.06 and 0.94 male/ha at the 13 sites where they were detected (mean = 0.25 male/ha, SD = 0.25). Male density was not correlated with site area (rs = 0.36, P = 0.1140, n = 21), but was correlated with the coverage of perennial crops (rs = 0.46, P = 0.0371, n = 21) and forests (rs = -0.46, P = 0.0361, n = 21) in the surrounding landscape. There was no association between male density and vegetation characteristics measured in quadrats. Male density was higher, however, at sites where hedgerows were noted (0.31 male/ha vs 0.08 male/ha; χ2 = 5.12, P = 0.0236), but did not differ between sites with respect to the presence of other habitat features. Overall, 64 plant species were recorded at the 27 sites. Poa spp. (bluegrass), Elytrigia repens (L.) Gould (Quackgrass), Potentilla argentea L. (Silver Cinquefoil), Potentilla reptans L. (Creeping Cinquefoil); Danthonia spicata (L.) Beauv. ex Roemer & J.A. Schultes (Poverty Oatgrass), Fragaria virginiana Duchesne (Wild Strawberry), and Phleum pratense L. (Timothy) were all observed in >50% of sites. In addition to D. spicata and P. argentea, several other species typical of dry sandy soil such as Physalis heterophylla Nees (Clammy Ground-cherry), Rumex acetosella L. (Sheep Sorrel), and Comptonia peregrina (L.) Coult. (Sweet Fern), were detected in both groups of fields. Although highly conspicuous at several sites, Common Mullein was not dominant in quadrats in any site. Fields with and without sparrows had similar plant communities; the DCAs performed on species occurrence and cover using all or a subset of species did not reveal any clear pattern in site positioning in the ordination plots. Mean site scores of the two groups of sites did not differ along the first (χ2 < 1.18, all P > 0.2773) and second (χ2 < 2.31, all P > 0.1283) axis for all ordinations. Mean coverage of dominant species also did not differ between sites with and without sparrows. Discussion Past studies have shown that fields used by Grasshoppers Sparrows are generally grass-dominated with short vegetation, shallow litter, and reduced vegetation density and shrub cover (Balent and Norment 2003, Bollinger 1995, Chapman et al. 2004, Delisle and Savidge 1997, Frawley and Best 1991, Scheiman et al. 2003, Scott et al. 2002, Whitmore 1981). Hayfields and old fields where Grasshopper Sparrows were detected in southwestern Québec had this same vegetation structure; our vegetation variable metrics were all within previously reported values measured at breeding sites in the eastern USA (Dieni and Jones 2003; Mitchell et al. 2000; Whitmore 1979, 1981). This species inhabits a variety of grassland types in North America (Dechant et al. 1998, Earley 2007, Speirs and Orenstein 1967, Vickery 1996) as in our study region, where they were found in old fields, pastureland, and hayfields. There was no difference between sites with and without sparrows, 142 Northeastern Naturalist Vol. 17, No. 1 either with respect to their structural components and heterogeneity or in their plant species composition. Since we selected potential breeding sites based on their apparent suitability, these sites may not have offered sufficient variability to allow clear distinctions between suitable and unsuitable sites; patch-level differences might have been revealed had we randomly selected study sites amongst all cropfields in the region, including high-density hayfields and row-crop fields. In our study, then, all selected sites might have been suitable for Grasshopper Sparrows, but were possibly not occupied because breeding-bird density may not have been near saturation (Jobin et al. 2008, Rotenberry and Knick 1999). Although a moderate amount of shrub cover is often mentioned as being a key habitat requirement for Grasshopper Sparrows (Mitchell et al. 2000, Vickery 1996), regularly mowed hayfields lacking perches were largely used as breeding sites in our study region as elsewhere in North America (Delisle and Savidge 1997, Mitchell et al. 2000 and references therein). In addition, Knodel-Montz (1981) and Vickery and Hunter (1995) have shown that adding artificial song perches did not change Grasshopper Sparrow density, which would appear to lessen the importance of that habitat component for Grasshopper Sparrows. Both landscape-scale and on-site habitat parameters need to be considered when seeking grassland bird-habitat relationships (Bakker et al. 2002, Chapman et al. 2004, Cunningham and Johnson 2006, Hamer et al. 2006, Rotenberry and Knick 1999). We did not find any difference between used and unused grasslands at the patch-level, but we detected differences at the landscape scale where sites used by Grasshopper Sparrows were embedded within a perennial crop-dominated matrix and where forest cover was reduced. This finding is in agreement with several studies that have shown the importance of high grassland and reduced forest cover in landscapes surrounding Grasshopper Sparrows and other grassland birds’ breeding habitats (Bakker et al. 2002, Browder et al. 2002, Grant et al. 2004, Hamer et al. 2006, Renfrew and Ribic 2008, Ribic and Sample 2001, Veech 2006). In addition, this species is generally considered area-sensitive (Davis 2004, Johnson and Igl 2001), and fields used by Grasshopper Sparrows were larger than those where they were absent, which concurs with other studies conducted in North America (Bollinger 1995, Helzer and Jelinski 1999, Herkert 1994, Renfrew and Ribic 2002, Vickery et al. 1994). Grasshopper Sparrows were dectected at only 3 of the 23 historic sites outside of the Pontiac Region in 2004 (Jobin and Falardeau 2005), and the only remaining well-established Grasshopper Sparrow population in Québec is now in the Pontiac region, where urban sprawl and corn production are rapidly expanding (Jobin 2003). We observed a rapid conversion of suitable habitat during our study period, when 4 of the 36 originally selected sites were ploughed before the second field season; however, several sites where sparrows were detected were under annual crop and strawberry production 2 to 3 years before the surveys. These findings suggest that habitat management and restoration activities 2010 B. Jobin and G. Falardeau 143 can be beneficial within a short period of time. Although the core of the breeding population is in the Midwest, the precarious status of Grasshopper Sparrows in Québec, as in several regions of the northeast, calls for immediate conservation initiatives at both the regional and national levels, and efforts to stabilize or enhance local populations in the northeast are justified (Wells and Rosenberg 1999). Conservation and stewardship activities should be encouraged to secure large tracts of grasslands in this region (Balent and Norment 2003, Dechant et al. 1998, Sample and Mossman 1997, Troy et al. 2005) and to promote farming practices that ensure that suitable breeding habitats remain for this declining species. 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