Effects of Habitat Edges on Wintering Bird Occupancy in Umstead State Park AEC501 Lab Project Group 3: Connor Winfield, Jackie Hausle, Paul Lasley, Rebecca Goodnight, Sabrina Dixon, and Whitney McCurry
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Effects of Habitat Edges on Wintering Bird Occupancy in Umstead State Park
AEC501 Lab Project Group 3: Connor Winfield, Jackie Hausle, Paul Lasley, Rebecca Goodnight, Sabrina Dixon, and Whitney McCurry
Study Aims
● To further explain the effects of habitat fragmentation on urbanized landscapes.
● Analyze the differences of species composition from edge habitat (boundary) to core habitat (middle of park).
● Expand on previous research (Murcia 1995) of edge effects on species composition.
● Specifically focused on wintering bird populations in William B. Umstead State Park.
Background
William B. Umstead State Park
● Located in Northwest Raleigh● 5,600 acres of old growth forest● 3 lakes with various creeks interspersed ● US-70 to the North● Interstate I-40 to the South● Raleigh-Durham International to the West● Suburbs to the East
Question
● What are the effects on occupancy for various bird species as the distance from the park boundary increases and the surroundings shifts to a less developed core habitat?
Methods: Collection● Three collection days
○ Mar 17○ Mar 18○ Third rep weekday between Mar 19-Mar 23
● 3 trails - Cedar Ridge, Graylyn, and Company Mill- consistent observers
● 22 points on each trail, 100 meters apart ● Unlimited radius● Recorded calls or sightings,
presence/absence data● Made note of number of visitors seen on
each trail● Flaws?
Methods: Analysis● Presence 12.7● Focused on 11 species● 3 models
○ Null: No Covariates○ Distance: Distance from boundary into park, main study variable○ Trail Use: Comparing Heavily traversed trail to less used trails
■ Confounded with observer and trail variable● Statistics: based on maximum model likelihood estimates
○ AIC: Model selection metric○ ΔAIC: Measurement from the top-ranked model’s AIC ○ Weight: Measure of support for each model being the best model
Results
Overview● 39 species found
○ 34 Passerines○ 4 Piciformes○ 2 Accipitriformes
● 11 chosen for analysis
Naive Occupancy Compared to Expected Occupancy● Presence adjusts for
detection○ Based on percentage of
replicates where species was detected
● Disparity between Naive/Calculated indicates detection probability
○ Inverse relation
Model ReliabilityAmerican Robin Mourning Dove
AIC ΔAIC Weight AIC ΔAIC Weight
Null 147.03 0 0.857 Null 181.26 0 0.463
Distance 152.36 5.33 0.0596 Distance 182.73 1.47 0.222
Trail Use 151.69 4.66 0.0834 Trail Use 182.03 0.77 0.315
Brown-headed Nuthatch Northern Cardinal
AIC ΔAIC Weight AIC ΔAIC Weight
Null 117.27 3.3 0.1204 Null 218.73 6.67 0.0356
Distance 113.97 0 0.6271 Distance 220.19 8.13 0.0172
Trail Use 115.79 1.82 0.2524 Trail Use 212.06 0 0.9499
Model ReliabilityCarolina Wren Pine Warbler
AIC ΔAIC Weight AIC ΔAIC Weight
Null 197.64 16.35 0.0003 Null 222.44 10.47 0.0053
Distance 199.48 18.19 0.0001 Distance 238.68 26.71 0
Trail Use 181.29 0 0.9996 Trail Use 211.97 0 0.9947
Dark Eyed Junco Red-Bellied Woodpecker
AIC ΔAIC Weight AIC ΔAIC Weight
Null 128.36 24.12 0 Null 153.63 1.4 0.2956
Distance 126.13 21.89 0 Distance 155.62 3.39 0.1093
Trail Use 104.24 0 1 Trail Use 152.23 0 0.5952
Model ReliabilityEastern Towhee Tufted Titmouse
AIC ΔAIC Weight AIC ΔAIC Weight
Null 127 27.47 0 Null 182.26 4.57 0.0824
Distance 128.57 29.04 0 Distance 191.71 4.02 0.1084
Trail Use 99.53 0 1 Trail Use 177.69 0 0.8092
Golden Crowned Kinglet
AIC ΔAIC Weight
Null 155.39 45.04 0
Distance 157.02 46.67 0
Trail Use 110.35 0 1
Model Reliability: Discussion
● Preferred Model has lowest AIC○ Preferred compared to other models, not to best possible model
● Our Results: ○ Trail Use: 8○ Distance: 1○ Null: 2
Occupancy v. Distance● Biological significance
○ Edge species○ Interior species
● Missing species due to presence parameters being violated
Species Breakdown Occupancy v. Distance
Species Breakdown Occupancy v. Distance
Species Breakdown Occupancy v. Distance
Discussion● Trail use model preferred in 8 species
○ 2 light trails, 1 heavy trail: not enough replicates for significant analysis
○ Confounded with observer skill variable as well ● Surprising detection probability results?
○ Robin detection much lower than Dark Eyed Junco?
■ Why? ● Observer Bias ● Sampling Bias
Discussion
● Estimates of occupancy at set distances
○ Some species had naive occupancy of 1 (across 9 reps for each set distance)
○ So can’t run analysis● Most statistically insignificant
○ American Robin, Dark-Eyed Junco show statistically significant differences in occupancy between outermost and innermost data points
Acknowledgements ● Ted Simons for 99% of our avian identification knowledge● Shilo Felton and Mike Cove for Presence Instruction and Troubleshooting● Shilo Felton for constructive criticism along the way
Literature CitedBlair, R. B. (1996), Land Use and Avian Species Diversity Along an Urban Gradient. Ecological Applications, 6: 506–
519. doi:10.2307/2269387
Ewers, R. and Didham, R. (2005). Confounding factors in the detection of species responses to habitat fragmentation. Biological Reviews, 81(01), p.117.
Murcia, C.1995. Edge Effects in Fragmented Forests: Implications for Conservation. Trends in Ecology & Evolution 10:58-62.
Zurita, G., Pe’er, G., Bellocq, M. and Hansbauer, M. (2012). Edge effects and their influence on habitat suitability calculations: a continuous approach applied to birds of the Atlantic forest. Journal of Applied Ecology, 49(2), pp.503-512.
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