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Forest songbird communities

Libby Allard and Vanessa Fox
Biology Department, DePauw University
Summer 2005

Introduction
We collected data on songbird communities and habitat characteristics in three forested sites in the DePauw Nature Park.  We compared our data to data previously collected at forested sites in southern Ohio.  The Ohio sites were used for comparison because some species of songbirds with widespread distributions were only present in the Ohio sites.

Hypotheses
We hypothesized that the differences in songbird communities between Indiana and Ohio were due to age of the forest, composition of the forest, landscape fragmentation, and size of the forest. 

Methods
We conducted songbird surveys in three forested sites (QH, QS, and ARB) during May and June in 2004 and 2005.  We conducted four surveys per year at each site.  During each survey, we recorded locations of singing and calling birds throughout each site.  We transferred observations to composite maps for each bird species and looked for clusters to identify individual territories.  We estimated the number of breeding pairs based on the number of territories and singing males.  We collected vegetation data at randomly located plots and nest sites following the BBIRD protocol.

Results
Northern Cardinals were common at the Nature Park sites. We mostly observed this species along forest edges, such as powerlines, streams, and meadows.  Indigo Buntings and Eastern Towhees were also common at the two of the Nature Park sites and were absent from the Ohio sites.  The Indigo Bunting nests in low-growing shrubs in forested areas.  Acadian Flycatchers were more abundant in the Nature Park sites than in the Ohio sites.  Acadian Flycatchers are associated with mature forest habitat.  Ovenbirds were one of the most abundant bird species in the Ohio forests but were absent from the Nature Park sites.  Other bird species that were present in Ohio forests but absent in the Nature Park were the Black-and-white Warbler, Hooded Warbler, and Worm-eating Warbler.  These bird species nest on the ground or in low shrubs in forest habitat.  Cerulean Warblers were observed at one of the three Nature Park sites, Quarry South.  Population levels of the Cerulean Warbler were similar between Quarry South and the Ohio forests. 

Discussion
The forested areas in the DePauw Nature Park provide valuable habitat for a variety of songbirds.  The forests in the Nature Park are more fragmented with more extensive edge habitat and denser shrub growth compared to the Ohio sites.  This is why we observed higher numbers of Northern Cardinals, Eastern Towhees, and Indigo Buntings in the Nature Park.  We are not sure why the Ovenbird and other ground-nesting birds are absent from the Nature Park. We recommend that disturbance in the Nature Park forests be minimized to maintain the integrity of the habitat.  Future research on songbird communities is important because it relates to the health of the ecosystem.  Future research could address additional questions such as:

  • What environmental factors limit the populations of the Cerulean Warbler?

  • Why are ground-nesting birds, such as the Ovenbird, absent from the Nature Park forests?

  • Does the abundance of invertebrates affect the composition of the forest songbird communities?

  • Is there a correlation between the amount of leaf litter and the composition of the forest songbird communities?

  • How do we promote forest health and minimize the spread of invasive plant species in the Nature Park without disturbing forest songbird habitat?

Table 1.  Songbird population levels, measured as number of breeding pairs per 10 hectares at three forested sites in the DePauw Nature Park (ARB, QH, and QS) and at forested sites in Ohio.

 

ARB

QH

QS

Ohio

Acadian Flycatcher

10.1

10.5

13.4

3.3

Eastern Wood-Pewee

4.6

5.5

2.3

1.9

Red-eyed Vireo

15.5

9.4

8.4

10.5

Tufted Titmouse

5.5

7.7

8.3

0.5

Cerulean Warbler

0

0

4.7

2.6

Northern Parula

3.7

1.1

2.4

0

Ovenbird

0

0

0

10.2

Black-and-white Warbler

0

0

0

0.9

Hooded Warbler

0

0

0

2.3

Worm-eating Warbler

0

0

0

2.5

Scarlet Tanager

2.8

2.2

1.9

3.3

Eastern Towhee

7.3

2.8

4.2

0

Northern Cardinal

18.3

11.6

10.2

0.5

Indigo Bunting

11.0

3.3

10.7

0