Species-Specific Management (SSM)

The Blue-Gray Gnatcatcher

The blue-gray gnatcatcher (Polioptila caerulea), is an abundant summer resident within the southern Appalachian forest. It has a distinctive voice. However, the bird is small and few people know about it. The breeding area is typically below 1800 feet elevation. The bird has ecological, aesthetic, and economic importance to the wooded areas and should therefore be carefully managed.

These are birds of the mixed hardwood forests and wooded swamps (cypress, post oak, etc.) Although blue-gray gnatcatchers will feed and nest in any species of tree, favorite sites are forests containing oak and pine trees with an undergrowth of scrub oak. Planting or maintaining combinations of oak and pines will provide the best habitat for the bird; but planting or retaining any species of tree will be beneficial. It seems to make seasonal shifts in feeding behavior (Root 1967). Favorites in coastal areas at the edge of the Appalachians are are pocosins: oak, gum, cypress, elm, ash, cottonwood. Evergreen shrubs and trees need to be available for year-round foraging and protection. Blue-gray gnatcatchers have been documented using juniper species. Pines, will also provide habitat for insects, as well as provide refuge from predators.

Water is needed nearby, either standing or flowing sources, not for drinking but as breeding habitat for insects, the blue-gray gnatcatcher's main source of food. Standing water in land depressions or other low areas can provide water. Additionally, constructing ponds, ditches, and other water holes will help in achieving water needs.

Management suggestions include:

Nests and Nesting

1. Grasses, herbaceous plants, lichens, and spider webs need to be available for the gnatcatcher to use in building the nest. Small grass patches, dandelion, thistle, sycamore (seedballs), or other plant down should be available for nesting material. Additionally, flower blossoms, horse-hair, and fine strips of inner bark may also be used.
2. Blue-gray gnatcatcher nests can be saddled on a 1 to 2 inch diameter horizontal limb but are often found in a fork between an upright branch and a horizontal or slender one. Trees need to be allowed and encouraged to grow until this optimal size is reached.
3. Nests are found less than 25 feet from the ground in many different species of trees:

   apple, wing elm, black locust, bear oak, burr oak, post oak, white oak, red cedar, sweetgum, persimmon.

   However, the gnatcatcher seems willing to use any tree that provides limbs of the right size and arrangement for nesting, typically hardwood trees of sawtimber size.

4. Create small brushy openings in forests. These patches should be small so that open country predators are not encouraged. Tent caterpillars should not be eradicated unless they pose a serious defoliation threat. Silk from caterpillar nests is used along with spider webs for nest building.
5. Prevent forest fires, livestock disturbance, or other influences that would reduce understory and high herbaceous cover.

   Food

6. The diet of the gnatcatcher consists of longhorn beetles, caddis-flies and other Dipterans (flies) as well as gnats, wood-boring beetles, and spiders. Managing for or allowing conditions for these species would concurrently be managing for the blue-gray gnatcatcher. To encourage insect productivity, be sure the stream bottom has stable material such as stones, logs, and branches.
7. Foraging is done among leaves of trees. Snags and cavities are believed to be unimportant for this bird.
8. Limbs must be available in large quantities because foraging is done by landing on a limb and catching insects that fly off the limb to escape or others that fly within sight.
9. Add small measured amounts of fertilizer high in nitrogen and phosphorous to the water sources to encourage primary productivity of algae which are fed on by the larvae of insects.
10. Bird feeders are seldom used by blue-gray gnatcatchers. However, during food shortages the birds will eat cornbread or commercial bird seed mixed with grated carrots.

    Predators and Losses

11. Exclude free-ranging domestic cats.
12. Increase buffer species as prey for sharp-shinned hawks (Accipiter striatus), screech owls (Otus spp.), and loggerhead shrikes (Lanius ludovicianus).
13. Avoid application of insecticides.

    People Management

14. Increase recreational value of the bird by encouraging bird watchers to visit the managed area.
15. Ensure access to the area through roads and trails.
16. In winter, blue-gray gnatcatchers migrate south to the Bahamas, the western Greater Antilles, Guatemala, and Honduras. Protect or encourage protection of wintering grounds by maintaining wooded areas. Population management requires becoming involved with forest conservation efforts in these areas.
17. Educate people about beneficial insect-feeding habits.
18. Educate foresters and farmers about insect foraging.
19. Educate bird watchers about the voice of this bird.

    Feedback

20. Conduct an annual census of gnatcatchers. Walk through the area along a route that does not turn back on itself and count the gnatcatchers that you see or hear. Walk this same route at the same time each spring and note changes in the tally. Late March or early April (period of nest-building activity) would be a good time to do this.

    Feedforward

21. Anticipate changes in populations of the gnatcatcher and reconcile differences in expected numbers and those observed (primarily those heard).

References

Root, R.B. 1967. The niche exploitation pattern of the bluegray gnatcatcher. Ecol. Monog. 37(4):317-350.

Bent, A.C. 1949. Life histories of North American thrushes, kinglets, and their allies. US Natl. Museum, Bul 196, Washington p. 344-364.

LeGrand, H.E., Jr. and P. B. Hamel. 1980. Bird-habitat associations and southeastern forest lands. Clemson Univ., Clemson, SC p. 98, 176.

Contributions byDale Woods (1985), Laura Ellen Hill (1993), Christine Vaisvil (1993), York D. Grow (1992), Ernest W. Buford (1992), Department of Fisheries and Wildlife Sciences, Virginia Polytechnic Institute and State University, Blacksburg, VA 24061-0321

Submitted by Robert H. Giles, Jr.

This Web site is maintained by R. H. Giles, Jr.
Last revision July 17, 2002.