The Marbled Murrelet Brachyramphus marmoratus is considered a threatened seabird under US federal legislation; it flies up to ~80 km inland to nest on limbs of old-growth coniferous trees. Little is known about intra-annual patterns in movement rates or flight altitudes of murrelets at inland sites, yet this information is critical for evaluating collision risk at wind turbines and other tall structures and the potential for disturbance impacts from timber operations (e.g. road construction). We used marine radar to study murrelets year-round during the peak dawn activity period (n = 78 mornings) at three high-use sites in northern California. Murrelet passage rates were relatively low in winter (11%–47% of summer rates), increased in spring, peaked during the summer breeding period (late April–July) and were lowest during the fall molt period. We observed large among-site differences in mean flight altitudes of murrelets between two sites along the coast (93 +/- 3 m and 98 +/- 3 m above ground level [agl]) and a single site further inland (257 +/ - 6 m agl). Flight altitudes during periods with fog or scattered rain did not differ significantly from altitudes during periods without precipitation. These results demonstrate the potential for different levels of disturbance and collision risk throughout the year and the importance of incorporating seasonal and site-specific variation into collision risk models. These results also provide new information for US Fish and Wildlife Service guidelines being developed for studies of murrelets at proposed wind energy projects.
Sanzenbacher, P. M., B. A. Cooper, J. H. Plissner, and J. Bond. 2014. Intra-annual patterns in passage rates and flight altitudes of Marbled Murrelets Brachyramphus marmoratus at inland sites in northern California. Marine Ornithology 42:169–174.