The effects of roadway mortality on barn owls in southern Idaho and a study of ornamentation in North American barn owls

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This thesis is presented in two sections, describing investigations of roadway mortality and ornamentation of barn owls (Tyto alba) in southern Idaho. Research objectives were to 1) quantify roadway mortality of barn owls along a 248-km stretch of Interstate 84, 2) examine the factors that influence roadway mortality of barn owls in this area, 3) refine estimates of roadway mortality by performing bias experiments, and 4) investigate the potential relationships between ornamentation (in the form of ventral spottiness) and quality in North American barn owls (T. a. pratincola) and compare results of this Idaho study to similar studies of European barn owls (T. a. guttata and T. a. alba). After running bias experiments and calculations, Boves determined a total mortality rate of 163.7 owls/100 km/year and a second year mortality rate of 260.9 owls/100 km/year (higher than any previously recorded, including in Great Britain, where local extinction near major roadways have been reported). Boves found that juvenile and female barn owls were killed more often than adults and males, respectively; females were more commonly killed most of the year, but males were more commonly killed from April to June; and that there is seasonal variation in mortality. Death in various habitat areas is also discussed. Roadway mortality may have the potential to alter demographics of the barn owl population. Regarding ornamentation, female barn owls were twice as heavily spotted as males, but Boves detected no relationship between spottiness and quality in females. However, in males, he detected relationships between spottiness and two quality measures: heart fat and wing length.