NESTING ECOLOGY AND SITE FIDELITY OF GRASSLAND SPARROWS ON RECLAIMED SURFACE MINES IN PENNSYLVANIA
Open Access
- Author:
- Stauffer, Glenn E.
- Graduate Program:
- Ecology
- Degree:
- Master of Science
- Document Type:
- Master Thesis
- Date of Defense:
- March 17, 2008
- Committee Members:
- Duane R Diefenbach, Thesis Advisor/Co-Advisor
- Keywords:
- site fidelity
nest site selection
Reclaimed surface mines
Grasslands
nest survival - Abstract:
- Population declines of many migratory grassland bird populations in North America over the last several decades are thought to be the result of widespread loss of suitable breeding habitat. However, reclamation of surface mining operations in the midwestern and eastern United States has created breeding habitat for many grassland bird species. In western Pennsylvania, >35,000 ha of reclaimed surface mine grasslands are occupied by grasshopper sparrows (Ammodramus savannarum), Henslow’s sparrows (Ammodramus henslowii), and Savannah sparrows (Passerculus sandwichensis) in densities comparable to traditional grassland habitats. Henslow’s sparrows in Pennsylvania nest almost exclusively on reclaimed surface mines. Many species of grassland birds suffer increased nest predation on small (<100 ha) grasslands, and although successful reproduction of grassland sparrows has been documented on large (≥1,000) reclaimed mine grasslands, most reclaimed mine grasslands in Pennsylvania are small (≤100 ha) and nesting success has not been quantitatively described. To assess habitat suitability of reclaimed mine grasslands for nesting grassland sparrows, I investigated nest survival, nest site selection, and site fidelity of grasshopper, Henslow’s, and Savannah sparrows on four reclaimed surface mines in Clearfield and Clarion counties in western Pennsylvania, USA, in 2006 – 2007. There were few clear and consistent patterns in nest site selection, but, in general, all three species placed nests in areas with few shrubs, even though they frequently used shrubs as perches. Henslow’s sparrows placed nests in deeper litter than grasshopper and Savannah sparrows. Henslow’s and Savannah sparrows tended to avoid steep slopes more than grasshopper sparrows, and grasshopper and Henslow’s sparrows preferred areas where the view to the horizon was not steep. All three species avoided placing nests in areas with extensive bare ground. Grasshopper and Henslow’s sparrow nests that were well concealed were less likely to fail than highly visible nests, and nests in areas with a deep litter layer were more likely to fail than nests in shallow litter. Savannah sparrow nests in areas with high visual obstruction by vegetation were less likely to fail than nests in areas with sparse and short vegetation. Daily probability of survival for grasshopper sparrow nests followed a quadratic seasonal trend where survival was greatest early and late in the breeding season. Survival of Savannah sparrow nests followed a decreasing linear seasonal trend. There was no seasonal trend in survival of Henslow’s sparrow nests. For all three species, nest survival was greater on days with rainfall events, and for nests of grasshopper and Henslow’s sparrows, but not Savannah sparrows, survival increased with increasing maximum daily temperatures. Overall nest success was 0.422 (95% CI = 0.362 – 0.493) for grasshopper sparrows, 0.369 (95% CI = 0.288 – 0.472) for Henslow’s sparrows, and 0.158 (95% CI = 0.066 – 0.379) for Savannah sparrows. Average annual apparent survival was 0.41 (95% CI = 0.31 – 0.54) for male grasshopper sparrows and detection probability was 1. For male Henslow’s sparrows, average annual apparent survival was 0.33 (95% CI 0.10 – 0.68) and detection probability was 0.43 (95% CI 0.08 – 0.87). Male grasshopper sparrows banded in 2006 were 5.6 (95% CI = 1.7 – 18.5) times more likely than females to return in 2007, but the female return rate likely was underestimated because I could not estimate a detection probability. Measures of reproductive success poorly predicted probability of return for both males and females. The median inter-annual territory shift was greater for female grasshopper sparrows (median = 69 m) than for male grasshopper sparrows (median = 33 m), and both males and females that had at least one successful nest in 2006 shifted territories shorter distances in 2007 than birds that had no successful nests in 2006. No returning female Henslow’s sparrows were detected. Of 30 male and 14 female Savannah sparrows present on the study areas in 2006, 11 males (37.7%) and 2 females (14.3%) were seen in 2007. Simulations of finite rates of population increase, λ, suggested that reproductive success of grassland sparrows on my study areas, especially of grasshopper and Henslow’s sparrows, was adequate to maintain stable populations. Lambda was more sensitive to juvenile survival than to adult survival, and for grasshopper and Henslow’s sparrows, exceeded 1 when juvenile survival was ≥0.2. When survival of juvenile Savannah sparrows was 0.2, λ was >1 only when adult survival was 0.6, but always was >1 when juvenile survival was ≥0.4. Results of this study confirm that reclaimed surface mines likely support sustainable populations of grasshopper, Henslow’s, and possibly Savannah sparrows, and thus can play an important role in the conservation of these species in Pennsylvania. This especially is the case for Henslow’s sparrows in Pennsylvania, which nest almost exclusively on reclaimed surface mine grasslands. Reclaimed surface mines require less active management that other grasslands to prevent succession to woody species, and also generally are not attractive for agricultural purposes. Consequently, and in light of relatively poor reproductive success on of these species on agricultural grasslands, reclaimed surface mines are ideally suited for management as grassland bird habitat.