Marine Ornithology

Understanding movements of small seabirds has been particularly challenging due to limitations in tracking technology. As tracking devices become smaller and more powerful, and are deployed on smaller bird species, they need to be evaluated. We assessed whether small, platform terminal transmitters (PTTs; 5 g) could be used to study the nesting, movement, and foraging behaviors of the Threatened Marbled Murrelet Brachyramphus marmoratus in Oregon, US. We attached PTTs that transmitted locations and temperature measurements through the Argos satellite system to seven adult murrelets. We fit continuous-time correlated, random-walk models to location data to examine coarse movement patterns and determine whether murrelets were moving inland to potential nesting habitat. We used temperature measurements from the PTTs to examine murrelet diving patterns, indicative of foraging. Sixteen independent movements appeared to be consistent with inland movements. However, the PTT-tagged murrelets appeared to be on the ocean during nearly all of these movements, based on concurrent temperature readings. To further assess the utility of PTTs in locating murrelet nests, we deployed 3 PTTs in trees within suitable nesting habitat. Naive observers required 2-9 d to attain sufficient high-quality locations to attempt to locate these PTTs, and 4-13 h of searching to locate the exact trees. The PTTs we tested can be useful for describing coarse patterns of movement and foraging, but are not an improvement over VHF transmitters for locating nests. All of the tagged murrelets ceased movement during the course of the study. Three were found dead, and the rest were unrecoverable. We suspect that tagging negatively affected welfare of these birds. We recommend waiting for future versions of these tags that weigh less and include GPS technology before deploying them on small diving seabirds such as the Marbled Murrelet.