Suzanne Reeve and Dr. Brian A. Maurer, Zoology

The distribution and life history characteristics of organisms can be significantly affected by structural variation in their habitats. One major type of variation is spatial arrangement and whether a habitat extends continuously or exists in small, fragmented patches. The effects of this variation have been documented in organisms from fruit flies (Jaenike 1978) to Amazonian beetles (Klein 1989) to songbirds (Andren and Angelstam 1988, Gates and Gysel 1978). According to research findings and theoretical prediction, many significant consequences of habitat fragmentation are caused by an increased ratio of habitat edge length to area. Studies indicate that increased edge length creates greater opportunity for predator invasion (Wilcove 1985) and brood parasitism, as well as increasing exposure to wind and weather extremes (Jarvis 1993). In addition, a smaller habitat size may mean a decreased quality or quantity of food, possibly resulting in stunted rates of reproduction and growth (Moller 1991). Because habitat fragmentation can correlate with species declines due to the factors outlined above, it is important to understand what happens to animal populations living in fragmented habitats in order to effectively plan for species conservation.

To find out more about the effects of habitat fragmentation in songbirds, I decided to participate in a continuing research project designed in 1992 by Dr. Brian A. Maurer, currently a professor in Brigham Young University’s Department of Zoology, and Marc-Andre Villard, then employed in Dr. Maurer’s lab. The project studies a population of house wrens nesting in an area of aspen forest in Uintah National Forest in north central Utah. The study population nests in 95 nest boxes which have been placed in seven aspen patches, varying in size from 0.6-1.2 ha, and in one large, contiguous stretch of aspen forest, known as the control plot. This habitat is naturally fragmented, so the population nesting there will not be affected by logging, grazing, or other disturbances commonly encountered in habitats damaged by man. Because of the negative consequences of fragmentation described above, I hypothesized in my proposal that 1) over the course of several breeding seasons, a majority of dispersing wrens will move from habitat fragments into consolidated habitat areas; 2) wrens nesting in a large, continuous habitat will have greater reproductive success than those nesting in patches; 3) egg and nestling predation will be greater in habitat fragments than in contiguous areas.

I carried out my study in May-July 1998, visiting the study site two to three times a week during that time and making notes of the wrens’ nesting behavior, including dates of nest box occupation, egg laying, and egg hatching, and numbers of eggs and fledglings in active nests. Nest box occupation overall has been declining over the past several years at the site due to unknown causes, and this year the population reached its lowest point: in the control plot, for example, only four out of 49 nest boxes were active during the time of my observations.

Health problems beginning in June and July cut short my research activities in the field, and I have not yet been able to completely compile the data from this season. I do intend to continue with this research as circumstances permit, however, using data from the previous six seasons (1992-1997) and from the partial 1998 season, to test my hypotheses about how habitat fragmentation has affected this population of songbirds in one of Utah’s national forests.

Literature Cited

1. Andren, A., and P. Angelstam. 1988. Elevated predation rates as an edge effect in habitat islands: experimental evidence. Ecology 69:544-547.
2. Gates, J.F. and L.W. Gysel. 1978. Avian nest dispersion and fledging success in field-forest ecotones. Ecology 59:871-883.
3. Jaenike, J. 1978. Effect of island area on Drosophila population densities. Oecologia 36:327- 332.
4. Jarvis, P.J. 1993. Environmental changes. Pp. 42-85 in Furness, R.W. and J.J.D. Greenwood, eds. Birds as Monitors of Environmental Change. London: Chapman and Hall.
5. Klein, B.C. 1989. Effects of forest fragmentation on dung and carrion beetle communities in central Amazonia. Ecology 70:1715-1725.
6. Moller, A.P. 1991. Clutch size, nest predation, and distribution of avian unequal competitors in a patchy environment. Ecology 72:1336-47.
7. Wilcove, D.S. 1985. Nest predation in forest tracts and the decline of migratory songbirds. Ecology 66:1211-1214.