Status and breeding ecology of the loggerhead shrike in Virginia
MetadataShow full item record
Although loggerhead shrikes (Lanius ludovicianus) are still relatively widespread, Breeding Bird Survey results indicate that breeding population have declined substantially in Virginia and other parts of the species' range. Loggerhead shrikes should be considered for federal threatened status. I studied breeding chronology, productivity, and habitat use of 20 loggerhead shrike pairs in 1985 and 36 pairs in 1986. Yearly productivity in this Ridge and Valley population was 2.44 young raised to independence per breeding pair. Shrikes selected eastern red cedars (Juniperus virginiana) and hawthorns (Crataegus spp.) as nest support more than expected based on availability. Shrikes selected more, produced more young in, and were more likely to reoccupy active pastures compared to other habitat types. Herbaceous vegetation structure can limit shrike prey availability and may be responsible for the differential productivity and reoccupancy in active versus idle pastures: These results led to the development of hypotheses to explain the shrike decline. Shrikes are very sensitive to changes in successional stages of grassland foraging areas. Changed land-use practices such as smaller areas of farmland and pasture, and larger fields and area of row crops, may partially explain the decline in Virginia. Changes in the intensity, phenology, or placement of cattle gazing can result in lowered shrike productivity and may have also contributed to the decline. Further studies of shrike reproductive, success, mortality, and habitat use should be conducted in stable and declining populations.
- Masters Theses