Thesis (M.S.)--University of Wisconsin-Madison. / Cover title. "Perf. rpt, MN E-1-18, study 440." eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references.

This thesis describes the behavioural ecology of South African fiscal shrikes through detailed field observations and experimental manipulations, and discusses these in the context of reproductive ecology, life history strategies, territoriality, and foraging theory. A population of fiscal shrikes was observed during the period October 1995-0ctober 1997 in a 336 Ha area of grazed bushveld near Pietermaritzburg, South Africa. Fiscal shrike reproduction coincided with the onset of the rainy season. Nests were placed in the centre or north-west regions of tree canopies and contained three or four eggs. Incubation and brooding were performed by females, and shading behaviour was observed in hot weather. Hatching and fledging success averaged 48%. High, exposed nests were less successful than other nests as they were prone to damage during inclement weather. There was a trend in life history strategies between equatorial and South African fiscal shrikes (an increase in clutch size, incubation and brooding durations, and territory size and a decrease in breeding season length), and between northern hemisphere Laniinae (increased intensity in the northern hemisphere), that could be explained by variability in precipitation and temperature, and clutch survival. Fiscal shrikes maintained individual or pair-held territories throughout the year using visual and vocal signalling. Territories averaged 2.2 Ha in area and almost all contained man-made structures. Territory size was inversely proportional to tall tree density, as trees were used for foraging. Fiscal shrikes resided in areas with few natural perch sites by utilising fence lines and overhead cables. When perch density was manipulated fiscal shrikes decreased and increased territory size accordingly. Fiscal shrikes were sit-and-wait foragers and primarily used perch-to-ground forays. The diet of breeding birds consisted of large invertebrates. Small items were consumed and larger items were cached or fed to offspring or females. Fiscal shrikes were central place foragers. Prey size increased in patches over 35 m from the nest. Perch height affected search area, which in turn affected foraging methods, search duration and subsequent movements. Perches may be the limiting resource for other sit-and-wait foragers and the manipulation of perch density could act as a conservation strategy for declining populations. / Thesis (M.Sc.)-University of Natal, Durban, 1998.

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I studied loggerhead shrikes (Lanius ludovicianus) in the Shenandoah Valley in Virginia from April 1987 to April 1988; factors affecting mortality rates wring the breeding season, fall dispersal, and winter were investigated., The high reproductive,success in this study was similar to that reported by other researchers in the United States. Reproductive success was different among varying grass heights and varying amounts of bare soil areas within 100 m of shrike nests; success was highest in habitats with numerous bare soil areas and medium grass. I radio-harnessed fledglings at a mean age of 56 days to document dispersal, fall home-range areas, and survival rates. During the postfledging dispersal period, survival rates were 100% fledglings dispersed at a minimum of 78 days of age, and fall home-ranges typically contained medium grass and numerous bare soil areas. These habitat characteristics may provide shrikes with increased invertebrate availability. Winter negatively affected the loggerhead shrike population in Virginia; raptor predation was the primary cause of subadult and adult mortality, and road kill was secondary. Shrikes moved from grassland areas to shrub-forest areas during inclement weather and preyed on small birds. Home-range sizes were larger during the winter than at other times of the year. I documented the occurrence of low levels of organochlorine and organophosphates in all birds analyzed for pesticide contamination. Also, I present statistical models to predict age and sex of loggerhead shrikes; wing chord and tail white on rectrix 5 were the most useful variables in discriminating sexes and wing chord was used in discriminating ages. More research is needed on the effects of raptors on shrike populations and on the role of foraging habitat on winter areas. / Master of Science

Although loggerhead shrikes (<i>Lanius ludovicianus</i>) 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 (<i>Juniperus virginiana</i>) and hawthorns (<i>Crataegus </i> 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. / Master of Science