An Assessment Of Songbird Habitat On Huntington Wildlife Forest, New York

Leah M. Burke

Getting help identifying unknown plant.

Introduction

Habitat is a critical component of the ecosystem for many migratory and non-migratory songbirds that has been attributed to changes in the abundance of a variety of songbird species. Awareness of the importance of habitat for Neotropical migrants has increased over the past decade as declines in the abundance of various songbird populations has been detected in the Northeastern United States. Currently it is not known whether the declines should be attributed to changes in wintering areas, habitat degradation, fragmentation, or change, or parasitism by the Brown-headed cowbird (Molothrus ater).

Both local vegetation complexity and habitat structure are factors that are linked to the abundance and diversity of bird species found in an area. Many other significant habitat variables have been identified in the literature, including: percent ground cover vegetation, coarse woody debris, canopy cover, canopy height, tree size classes, and the number of snags per hectare. Changes in habitat occur both naturally and as a product of human activities such as logging. These changes are important to recognize because habitat selection by songbirds is primarily affected by vegetative structure (DeGraaf et al. 1998). Some songbirds tend to be more susceptible to certain changes in habitat and vegetative structure than others (DeGraaf et al. 1998). In part this susceptibility can be attributed to the specialization of some Neotropical migrants to certain habitat types. DeGraaf et al. (1998) mention that there is a strong relationship between habitat structure and bird species composition that can be useful in assessing the effects of different forest management strategies at various scales (e.g. stand level versus landscape level) on bird communities.

veery

My objective was to investigate the relationships between observed changes in songbird abundance at Huntington Wildlife Forest and changes in habitat by comparing both songbird abundance and habitat data for 1988 and 2002. Bird species I chose to look at were the black-capped chickadee (Parus atricapillus), golden-crowned kinglet (Regulus satrapa), hairy woodpecker (Picoides villosus), ovenbird (Seiurus aurocapillus), and veery (Catharus fuscescens). I expected that the greatest changes in songbird abundance would be seen in forest stands that have been most recently cut, while I expected songbird populations to remain fairly stable in the old-growth forest.

black-capped chickadee

Methods

Habitat Sampling
Sampling of habitats occurred from mid-June through early August 2002. Nested vegetation plots were used in an 11.4 m radius circular plot, with a permanently marked plot center. Four transects 11.4 m long were laid out in each cardinal direction. Eight 1m2 plots, two on each 11.4 m transect (one at 5 m and one at 10 m from plot center), were used to estimate the percent cover of the following variables: Live Tree (any trees and seedlings), Log, Stump/Snag, Woody plant (including honeysuckle (Lonicera sp.) and witch-hobble), Moss, Grass/Sedge, Fern, Forb (including Rubus sp.), Leaf Litter/Twig/Branch, bare Soil, and bare Rock.

Evaluating percent ground cover.

Species and dbh was recorded for all trees and snags when possible. All trees, including snags, greater than 2.54 cm (1 in) in diameter at breast height (dbh at 1.3 m) were measured on a 5 m radius plot. Coarse woody debris (CWD) types (i.e. stump, snag, log) greater than 2.54 cm dbh were recorded on the 5 m radius plot and placed into decay classes following Maser et al. (1979). Canopy cover and shrub layers were measured at 5 points at 2 m intervals from the center of the plot out to 10 m on each of the four transects. Canopy cover was evaluated using an ocular estimation tube.

Evaluating canopy cover.

Results
In each area, different tree species showed changes in mean dbh and number of trees from 1988 to 2002. In the Hare Area, balsam fir has decreased from 15.4 ± 7.7 cm to 8.4 ± 5.5 cm dbh while red spruce has changed from 13.9 ± 5.8 cm to 12 ± 7 cm. In the Maple Sale, changes in beech, pin cherry, red spruce, striped maple, white ash, and yellow birch were all found to be significant. The mean dbh increased while the number of trees decreased for the following species: beech (2.6 ± 3.7 cm to 8.5 ± 7.6 cm), pin cherry (3.8 ± 1.7 cm to 9.2 ± 3.5 cm), striped maple (1.4 ± 0.8 cm to 4.8 ± 2 cm), white ash (1.3 ± 0.5 cm to 41.8 ± 1.8 cm), and yellow birch (1.6 ± 0.8 cm to 6.7 ± 6.4 cm). Red spruce in the Maple Sale increased in both mean dbh and the number of trees from 2 ± 0 cm to 6.9 ± 4.3 cm. In the Natural Area, number of beech and eastern hemlock trees increased while their mean dbh decreased. The mean dbh of beech decreased from 15 ± 5.7 cm to 9.1 ± 8.7 cm and eastern hemlock from 51.5 ± 9.3 cm to 36.1 ± 8.7 cm. Yellow birches have increased in number and mean dbh in the Natural Area from 31 ± 7.5 cm to 38.6 ± 23.9 cm.

There were significant changes in mean percent ground cover in the Hare Area for percent Live Tree and CWD. Percent Live Tree has increased from 1988 to 2002 (1.2 ± 1.4 to 5.5 ± 2.2) while the percent of CWD has decreased from 1988 to 2002 (6.5 ± 4.7 to 3.7 ± 2.6). In the Maple Sale, mean percent Woody vegetation was found to decrease (22.1 ± 13.3 to 3.9 ± 7.1) while percent Live Tree, Woody, Forb, Fern, and Mean Green increased. Live Tree increased from 0.9 ± 0.6% in 1988 to 12.9 ± 7.4% in 2002, Forb from 1.3 ± 1.6% to 4 ± 3.4%, Fern from 7.4 ± 5.7% to 14.8 ± 5.7%, and Mean Green from 9.5 ± 7% to 19 ± 8.2%. In the Natural Area, changes in mean percent cover of Live Tree, Fern, Forb, Green, and Veg all increased from 1988 to 2002. Live Tree increased from 1.7 ± 2.9% to 8 ± 4.4%, Fern from 4.5 ± 3.1% to 16.8 ± 4.6%, Forb from 0.6 ± 0.9% to 5.7 ± 5.2%, Green from 5 ± 3.3% to 22.7 ± 8.4%, and Veg from 22 ± 13.6 in 1988 to 44 ± 9.8 in 2002.

Recording habitat data.

Songbird Abundance
There were no trends in relative abundance of black-capped chickadees, golden-crowned kinglets, hairy woodpeckers, ovenbirds and veeries in the Maple Sale, Hare Area, and Natural Area from 1983 to 2002, with the exception of the ovenbird. The graph of ovenbird relative abundance has the suggestion of an increasing trend in the Maple Sale (R2 = 0.355). The ranges of relative abundance for each species are as follows: black-capped chickadee from 0.17 in all areas sampled to 0.36 in the Hare Area; golden-crowned kinglet from 0.16 in the Natural Area to 0.26 in the Hare Area; hairy woodpecker from 0.11 in the Maple Sale to 0.25 in the Natural Area; ovenbird from 0.11 in the Maple Sale to 0.35 in the Natural Area; and the veery from 0.13 to 0.34 in the Maple Sale.

Discussion
Changes that have occurred in the number and size (mean dbh) of tree species are for the most part those that would be expected with increased stand age. In the Maple Sale, many tree species declined in number but showed a trend of increasing size. The likely reason for this is that during forest regeneration many shade intolerant species were out competed for a place in the canopy. Trees that were recruited into the canopy then increased in dbh, while overall they decreased in number. In the Natural Area there has been a noticeable change in the mean dbh and number of beech trees. The reason for seeing an increased number of beech trees with a smaller dbh is probably beech bark disease, as this area has been one of the hardest hit on HWF. Since beech undergoes vegetative propagation, smaller beech trees have presumably regenerated from parent trees killed off by beech bark disease. Changes in mean dbh and number of both balsam fir and red spruce in the Hare Area can likely be attributed to the fact that both species are shade tolerant. There has likely been an increase in the number of smaller trees of each species in the understory, which would decrease the mean dbh. The mean dbh has probably decreased for red spruce as a result of the especially large increase in the number of stems between 1988 and 2002 (106 to 306 stems).

Significant changes in percent ground cover have occurred since 1988. Interestingly, most changes have occurred in the percent cover of Mean Veg (total of Live Tree, Woody, Fern, Forb, and Grass/Sedge combined). Both the Maple Sale and Natural Areas have shown an increase in the percent Mean Green cover category, while the Hare Area showed an increase in the percent Mean Live Tree and Mean CWD. The Natural Area also exhibited an increase in percent Mean Veg. In the Maple Sale the increase in percent Mean Green may be a direct result of stand history. According to King and DeGraaf (2000) shelterwood cuts have been shown to increase the understory structure of stands and maximize the diversity of plants within a stand. An increase in the percent Mean Green may also be a result of old skid trails, which visibly had a greater amount of ground cover, being in our nested vegetation plots. Increases in both percent Mean Green and Mean Veg in the Natural Area may be attributed to the greater presence of gaps in the canopy due to the damage or death of dominant tree species allowing greater light penetration to the forest floor. The increase in percent Mean Veg in the Natural Area may be related to increased growth of witch-hobble in the understory. It is probable that relatively little increase in understory vegetation has occurred in the Hare Area because very little light is able to penetrate through the canopy to the forest floor. Conifer forests also tend to have rather acidic soils, limiting the number and types of species that are able to establish in these types of forest.

Ovenbird

Implications
This study reveals that the relative abundances of selected songbird species at HWF have not significantly changed over the time period from 1983 to 2002, and more precisely between 1988 and 2002 when habitat inventory took place. However, during this time period significant changes in habitat have occurred due succession and to the different forestry management practices in each of the study areas. It appears that forestry management practices on HWF property have not adversely affected any of the avian species, but have increased habitat heterogeneity. Therefore if forestry management continues as it has, it is unlikely that any significant changes in songbird relative abundance will occur at HWF in the near future.

Literature Cited
DeGraaf, R.M., J.B. Hestbeck and M. Yamasaki. 1998. Associations between breeding bird abundance and stand structure in the White Mountains, New Hampshire and Maine, USA. Forest Ecology and Management 103:217-233.

King, D.I. And R.M. DeGraaf. 2000. Bird species diversity and nesting success in mature, clearcut and shelterwood forest in northern New Hampshire, USA. Forest Ecology and Management 129:227-235.

Maser, C., R.G. Anderson, K. Cromack, Jr., J.T. Williams and R.E. Martin. 1979. Dead and down woody material. pp. 78-95 in J.W. Thomas, ed.: Wildlife habitats in managed forests: the Blue Mountains of Oregon and Washington. USDA Agric. Handbook 553.

About the Author: Leah Burke
I am currently a senior majoring in Natural Resources at Cornell University. Upon completion of my undergraduate work in June 2002, I hope to attend grad school to pursue a M.S. in wildlife biology and management.

Contact info:
For further information on any of these projects, you can contact:
Adirondack Ecological Center: aechwf@esf.edu
Leah M. Burke: lmb47@cornell.edu