In Chapter One I present the findings of an artificial burrow experiment that was designed to examine how chamber size and tunnel diameter affect nest-site selection in burrowing owls. I provided two types of artificial burrow clusters: one offered three chamber sizes but a standardized tunnel diameter, and the other offered two tunnel diameters with a standardized chamber size. Upon their return to the study areas, owls presumably selected nest sites based on preferred chamber or tunnel dimensions within the cluster they selected. I monitored reproductive measures (number of eggs, number of young fledged) as a function of chamber or tunnel dimension to examine potential effects of ABS configuration on reproductive success.
Burrowing owls preferred the largest chamber size and smallest tunnel diameter available to them in the two different cluster types. Also, significantly more juveniles fledged from the largest chamber than from the second largest chamber in the clusters of three ABSs. This finding is important because most resource managers deploy chambers much smaller than the largest chamber in my experiment. In Chapter One, I discuss hypotheses that may explain the patterns of ABS choice witnessed in my experiments.
Chapter Two focuses on the diversity and abundance of ectoparasites of burrowing owls in southwestern Idaho and their potential effects on site reuse, and nestling growth, survival, and hematocrit levels. I identify the species of ectoparasites I collected from adult and juvenile owls, and describe their relative abundance on a per brood basis. Also, I discuss the results of an experiment I conducted that investigated the effects of ectoparasitism by comparing broods in which I experimentally reduced ectoparasite levels to broods in which natural levels of ectoparasites existed. To reduce ectoparasite levels, I dusted all individuals within a brood and their nests’ substrate with an insecticide.
I collected three species of flea, one species of lice, and one species of carnid fly from burrowing owls in my study areas. Ectoparasite levels were similar between years of my study and thus, ectoparasite levels had no influence on nest-site reuse between years. Levels of infestation also did not differ between two tunnel diameters or among three chamber sizes used by nesting owls. Ectoparasite level did not affect juvenile owl growth (mass and tenth primary length) or fledging success when analyzing brood averages. In my ectoparasite manipulation experiment, dusted and infested nests did not differ in rates of growth or hematocrit levels. Constraints and the lack of statistical power for this experiment are discussed in detail. Also, I discuss the ecology and potential effects on burrowing owls of each ectoparasite species I collected.
In Chapter Three I present the results of an experiment that examined the efficacy of short-distance relocations of occupied burrowing owl nests. Nests (N = 5) occurred in artificial burrow systems in a field that was being converted from grassland habitat to irrigated agriculture. Nests contained one to five juveniles that ranged from 27 45 d. Nest chambers and tunnels were moved (range: 72.5 258 m) from original nest areas to selected locations in a buffer strip that surrounded the field. Juveniles were transported to the new sites, but adults were expected to move the short distances on their own.
Overall, two families (40%) accepted their relocation sites, two families (40%) exhibited “site tenacity” towards their original nest areas, and one family (20%) dispersed from the immediate vicinity. I describe the characteristics of each successful and unsuccessful relocation. I also introduce hypotheses to potentially explain why certain relocations were or were not successful. I conclude this chapter with a discussion of the efficacy of active and passive relocation efforts, problems I encountered with my experiment, and suggestions to increase effectiveness of mitigation techniques similar to those I employed.
Belthoff, J.R. and B.W. Smith. 2003. Patterns of artificial burrow occupancy and reuse by Burrowing Owls in Idaho. Wildlife Society Bulletin 31:1-7.
Smith, B.W. and J.R. Belthoff. 2001. Effects of nest dimensions on use of artificial burrow systems by Burrowing Owls. The Journal of Wildlife Management 65:318-326.
Smith, B.W. and J.R. Belthoff. 2001. Identification of ectoparasites on Burrowing Owls in southwestern Idaho. Journal of Raptor Research 35:159-161.
Smith, B.W. and J.R. Belthoff. 2001. Burrowing Owls and development: results of short-distance nest relocations to avoid construction impacts. Journal of Raptor Research 35:385-391.