RESEARCH NOTES: EFFECTS OF RADIOTRANSMITTERS ON NATAL RECRUITMENT OF BURROWING OWLS

Abstract

Radiotelemetry often is used to estimate survival and home-range size, locate nests, and determine migration patterns and causes of mortality in birds (Amlaner and Macdonald 1980, White and Garrott 1990, Pride and Smith 1992, Kenward 2000, Millspaugh and Marzluff 2001). Most studies implicitly assume that radiomarked individuals behave and survive normally. Studies evaluating the effects of radiotransmitters on survival are not uncommon in waterfowl and upland game birds (Herzog 1979, Paquette et al. 1997, Bro et al. 1999) but are much less common for other avian taxa (but see Paton et al. 1991, Powell et al. 1998). Western burrowing owls (Athene cunicularia hypugaea) are listed as endangered in Canada, and populations have declined in many areas of the United States ( James and Espie 1997, Sheffield 1997, Kirk and Hyslop 1998, Desmond et al. 2000, Klute et al. 2003). To prevent further population declines and to design and implement effective recovery efforts, we need to identify which demographic parameter(s) are impaired in areas where owls are declining. Telemetry has proven useful in this regard and recent studies have affixed radiotransmitters to adult (Haug and Oliphant 1990, Sissons et al. 2001, Gervais et al. 2003, Rosenberg and Haley 2004) or juvenile (King and Belthoff 2001, Todd 2001, Todd et al. 2003) burrowing owls. Burrowing owls might be more inhibited by transmitters than other birds due to their use of narrow underground burrows. However, few studies have examined the effects of radiotransmitters on behavior or survival of burrowing owls (but see Clayton and Schmutz 1999; J. Gervais, Utah State University, personal communication). We were interested in the effects of radiotransmitters on juvenile recruitment into the local population (natal recruitment) because natal recruitment may be particularly important for recovery of burrowing owls in local areas. For example, endangered burrowing owl populations in Canada have had lower natal recruitment compared to owl populations near the center of their breeding range (Haug 1985, Haug et al. 1993). As part of a long-term study on natal dispersal and nestling mortality, we examined the effects of radiotransmitters on natal recruitment of burrowing owls in eastern Washington, USA.