Spatial Ecology of Breeding Least Bitterns in Northwest Missouri

We examined the spatial ecology of breeding Least Bitterns (Ixobrychus exilis) on Squaw Creek National Wildlife Refuge in northwest Missouri using radiotelemetry. We collected 1,585 locations for 60 individuals (28 males, 32 females) during 23 May–2 August 2005 and 6 June-18 July 2006. Pooled data for both males and females, and both years resulted in mean 50 and 95% fixed kernel home range use distributions of 37.6 (n = 25) and 223.2 ha (n = 25) for all individuals with ≥30 locations. The mean maximum distance traveled between telemetry observations was 2,147.1 m (n = 28). There were no differences in home range size or mobility between male and female Least Bitterns, although there were great variations between years with birds in 2006 using home ranges five times larger than those in 2005. Habitat use was disproportionate to availability with birds using sites with cattail (Typha spp.) and arrowhead (Sagittaria spp.) to a greater extent than available in both 2005 and 2006. One of eight pairs monitored successfully reared young, while females of seven other pairs renested with new mates. Apparent nesting success was low due to severe weather events and nest depredation. We did not observe double brooding. Our study demonstrates that Least Bitterns are capable of using much larger home ranges than previously observed.