Wooden Nest Boxes Found Cooler 

By Conley C. Black

Managed nest-box programs can significantly increase local populations of Eastern Bluebirds and other cavity-nesting species.  Poorly designed boxes, however, may become population sinks rather than source centers.  Internal box temperature is an important determinant of box success.  Bluebird eggs and nestlings, for example, cannot survive temperatures exceeding 107' F (41' C).

Several researchers have investigated construction materials and nest box temperatures.  Lawrence Zeleny in 1968 and Robert M. Patterson in 1980 studied wood, metal, and plastic bluebird boxes.  Wood Duck boxes also have been studied.  J. A. L. Mertens in 1977 developed a model predicting box temperature for any material and ambient temperature, but its complexity discourages amateur use.

The goal of this project was to examine the effects of construction material on nest box temperature and to develop a graphed model of the relationship.

MATERIALS AND METHODS

Surrounding air temperature and the interior temperatures of four nest boxes were recorded daily from March 26, 1996, to March 31, 1997.  Box 1 was a paper juice carton, modified from a design by Davis and Roca (1995).  Box 2 was designed by the author and constructed of aluminum.  Box 3 was constructed of 3/8inch (0.95 cm) plywood, similar to a design by Davis and Roca.  Box 4 was constructed of PVC pipe (Gilbertson 1991).  Each box had a screened horizontal entrance slot and two coats of white exterior latex paint.

The boxes were mounted five feet (1.5m) high and six feet (1.8 m) apart on a south-facing chain-link fence located five miles (8 km) south of Brooksville, Florida.  Liquid thermometers were placed in the boxes with the bulbs one inch (2.5 cm) above the floor.  A shaded surrounding-temperature-control station was established 75 feet (23 m) to the southwest.  Surrounding temperature, internal box temperature, cloud cover, and wind conditions were recorded at 2:30 p.m. each afternoon when air temperatures are near the daily maximum.  Cloud cover was characterized as sunny, partly cloudy, or overcast.  Wind speed was characterized as calm, breezy, or windy.  Only sunny days with no wind were used in the analysis.

RESULTS AND DISCUSSION

Observed temperatures were within the range of previously reported results, confirming that wooden boxes are cooler and paper boxes are warmer than those constructed of other materials.  PVC and aluminum boxes are between the two.  A maximum internal increase of 8' F (4.4' C) was recorded for the wooden box and increases of 10' F (5.5' C) and 16' F (8.9' C) were observed for the PVC and paper boxes respectively.

For these boxes, internal increases were proportional to the rising temperature of the surrounding air.  The aluminum box behaved differently.  Increases there were inversely related to rising air temperature.  It is not clear why this occurred.  A defective thermometer was suspected, but the instrument was tested and found to be reliable.

The data may be biased in some ways.  A maximum air temperature of 94' F (35' C) was observed on July 27, 1996.  Daily highs in west central Florida seldom exceed this value and temperatures above 1000 F (380 C) have been recorded less than 20 times since 1899.  Higher daily maximums, such as regularly occur in other parts of Nonh America, might produce different results.  Box status also must be considered.  Since occupied boxes are warmer than unoccupied boxes, these data probably underestimate actual brooding temperatures.

ACKNOWLEDGMENTS

The contributions of student intern John Berry were crucial to the success of this project. The Southwest Florida Water M2nagem@nt District provided funding and other resources.

LITERATURE CITED

Literature from the following publications was used in preparation of this article:

Bellrose, Frank C., and Daniel J. Holm 1994.Ecology and Management of the Wood Duck. Stackpole Books. Mechanicsburg, Pennsylvania. Blem, Charles R., and  Leann B. Blem.

Davis, Wayne H., and Phillippe Roca. 1995. Bluebirds and Their Survival. University Press of  Kentucky. Lexington, Kentucky.

Gilbertson, Steven L. 1991. New PVC House Attracts Bluebirds Not Sparrows. Sialia. 13:93-97.

Griffith, M. A., and T. T Fendley. 1981. Five-Gallon Plastic Bucket: An Inexpensive Wood Duck Nesting Structure. Journal of Wildlife Management. 45:281-284.

Hartley, D. R., and E. P. Hill. 1990. Effect of Heat in Plastic Nest Boxes for Wood Ducks. Pages 249-250 in L. H. Fredrickson, G. V. Burger, S. P. Havera, D. A. Graber, R. E. Kirby, and T. S. Taylor, eds., Pro. 1988 North American Wood Duck Symposium, St. Louis, MO.

Lotus Development Corporation. 1994. Lotus 1-2-3 Users Guide: Release 5. Lotus Development Corporation, Cambridge, Massachusetts.

McComb, William C., and Robert E. Noble. 1981 ' Microclimates of Nest Boxes and Natural Cavities in Bottomland Hardwoods..Journal of Wildlife Management. 45:284-289.

Mertens,j. A. L 1977. Thermal Conditions for Successful Breeding in Great Tits (Parus major L.). II. Thermal Properties of Nests and Nestboxes and Their Implications for the Range of Temperature Tolerance of Great Tit Broods. Occologia. 28:31-56.

Patterson, Robert M. 1980. More on Nesting Box Temperatures. Sialia. 2:15-18.

Pilny, Paul, Charles T. Grantham, Joseph N. Schuster, and Daniel L. Stankey. 1988. Soil Survey of Citrus County, Florida. United States Soil Conservation Service. Washington, D. C.

Radunzel, Lorissa A., Donna M. Muschitz, Vincent M. Bauldry, and Peter Arcese. 1997. A Long-Term Study of the Breeding Success of Eastern Bluebirds by Year and Cavity Type. Journal of Field Ornithology. 68:7-18.

Stains, Howard J. 1961. Comparison of Temperatures Inside and Outside Two Tree Dens Used by Racoons. Ecology. 42:410-413.

Van Balen, J. H. 1984. The Relationship Between Nest-Box Size and Breeding Parameters of the Great Tit and Some Other Hole-Nesting Species. Ardea 72:163-175.

Webb, D. R. 1987. Thermal Tolerance of Avian Embryos: A Review. Condor. 89:874-898.

Zeleny, Lawrence. 1968. Bluebird Nesting Box Temperatures. Atlantic Naturalist. 23:214-218.

(Mr. Black, a NABS member, can be reached at Southeast Florida Water Management District, 2379 Broad St., Brooksville, FL 34609.)