Nest exclosures do not improve Streaked Horned Lark nest success

ABSTRACT Improving the conservation status of rare and declining species often requires multiple strategies targeted at several vital rates. We report on one of several ongoing management actions intended to benefit the declining population of Streaked Horned Larks (Eremophila alpestris strigata). To improve Streaked Horned Lark fecundity, we employed predator exclosures (wire cages) around nests (N= 33 exclosed and 32 not exclosed) in 2009 and 2010 at two sites in Oregon and two in Washington with the goal of excluding larger birds, the primary lark nest predators. We found no statistically significant effect of exclosures on nest success. For exclosed nests, lower rates of nest predation (exclosed = 12%, unexclosed = 48%) were offset by higher rates of nest abandonment (exclosed = 27%, unexclosed = 0%). Nest abandonment was likely caused by a variety of factors including American Kestrels (Falco sparverius) perching on exclosures, and predation of adults associated with exclosed nests. Our results suggest that the current exclosure design does not improve Streaked Horned Lark fecundity and may negatively affect adult survival. To improve exclosure effectiveness, we recommend modifications that prevent kestrels from perching on exclosures and deny their access to the nest. We also recommend that modifications be applied in an adaptive management framework that includes close monitoring to assess their effectiveness, and subsequent adaptation that might include continued structural modification of exclosures or discontinued use on some or all sites.