Between-year movements and nest burrow use by burrowing owls in southwestern Idaho 1996 annual report / [book]

James R. Belthoff, R. Andrew. King
1997 unpublished
PROJECT SUMMARY Our study was designed to (1) monitor between-year movements of burrowing owls, (2) examine the important habitat features of nesting burrowing owls, and (3) assess the effects of the 1995 Point fire on the distribution and ecology of nesting burrowing owls. In 1996, we conducted studies in two areas, referred to as the Kuna Butte and Grand View study areas. We have now monitored nesting burrowing owls in the Kuna Butte study area for three years (since 1994), while 1996 was the
more » ... first year of our study in the Grand View area. We located a total of 32 nests in these two areas, 30 of which successfully fledged young during 1996. We individually marked 144 owls (N = 20 adults, 124 young), and banded an average of 3.9 ± 2.3 young per nest. Seven owls with previous histories in the Kuna Butte study area returned in 1996. These owls included four males and three females, all of which paired and attempted to breed during 1996. Of 52 nestling burrowing owls banded in the Kuna Butte study area in 1995, two (one male and one female) were detected in the area in 1996. This yields a first-year return rate of 0.038 (i.e., birds returning/birds banded). Return rates were higher for adults than for young, however. Of five males banded as breeders during 1995, two returned in 1996 (return rate = 0.4 returns per bird banded). Of 14 adult females originally banded in 1995, two returned to breed in 1996 (rate = 0.143 returns per adult female banded). Higher return rates for males may reflect higher mortality in, or greater dispersal by, females. The average distance moved by returning adult males (N = 2) was m. In each case, however, these males acquired a different mate in 1996 than they had in 1995. On the other hand, each of the adult females (N = 2) that bred in 1995 and returned in 1996 moved to a new nest burrow. These females bred 106 m and 503 m from their 1995 burrows, respectively. The young owls that returned bred 1.8 and 4.8 km from their natal burrows. Nest sites in the Kuna Butte (N = 18) and Grand View (N = 14) study areas differed significantly with respect to features of the burrow itself and the vegetation surrounding the nest site. In the Kuna Butte area, burrows were significantly larger, there were significantly more burrows within 10 m of the nest burrow, perches were closer, and there was more tumble mustard and cheatgrass than in the Grand View area. Within each study area, there were very few differences between used and unused burrows. However, we did find that unused burrows had significantly steeper tunnel entrances, which the owls may have avoided, and used burrows were significantly more likely to contain livestock manure, particularly in the Kuna Butte area. This manure was likely collected by the owls to reduce predation, parasitism, or provide some other unknown function. Finally, this study examined the use by nesting burrowing owls of recently burned areas in the Kuna Butte study area. All of the nest sites that were burned in 1995 by the Point (large fire near Initial Point) and other fires were reoccupied in 1996. Moreover, several additional burrows within the burned areas but with unknown histories were occupied by nesting owls in 1996. Because the fires occurred when young owls were capable of flight (i.e., late in the summer during the post-fledging period), no direct mortality of owls was observed. These initial observations suggest that the fires did not adversely affect the burrowing owls in this area.
doi:10.5962/bhl.title.63306 fatcat:rjkyw7iaibgdbccfqelqgyvvru