effects of habitat edges on wintering bird occupancy in

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.