South Puget Sound Streaked Horned Lark (Eremophila alpestris strigata) Genetic Rescue Study, Spring/Summer 2011

Hatchability of Streaked Horned Lark eggs in the Puget Lowlands of Washington State is extremely low relative to other grassland nesting birds at the same site and generally. Because genetic factors (inbreeding depression) appear to be a likely explanation, an effort to increase genetic diversity was initiated at the 13th Division Prairie on Joint Base Lewis and McChord. The most efficient and least disruptive genetic rescue technique is to translocate eggs from a population that is not showing evidence of low egg hatchability. If the resulting fledglings survive and breed at the new site, the local population should benefit from increased genetic diversity, and improved egg hatchability.

A total of eight breeding lark pairs occurred within the study area in Spring/Summer 2011. Fifteen nests were located, and twelve of the fifteen nests successfully produced 30 eggs. Nest building was first detected on 19 May; the first eggs were observed on 26 May; the first eggs hatched on 20 June; and the first fledgling was observed on 27 June. Four three-egg-clutches were translocated to Puget Sound nests, from Corvallis, Oregon. Eleven of the twelve translocated eggs hatched and were color banded as nestlings. A minimum of five fledglings survived and were observed foraging independently. Assuming that at least six Corvallis birds survived, we would expect at least one fledgling to survive its first winter and reproduce the following year. The local population of Streaked Horned Lark could be rescued by a single bird that returns and successfully breeds, which can lead to improved fitness and reduced extinction risk. Subsequent monitoring will determine whether these birds return to breed at 13th Division Prairie.