Figure 2.

Pathways between natal colonies (stars) and resight locations for six color-banded Caspian terns (each represented by a unique color). All six of these birds died on Rat Island (skull and crossbones) in 2023 during the HPAI outbreak where their bands were recovered. The circles represent non-natal colonies where these birds were resighted. These six birds are representative of the resight pathways followed by the other 10 banded terns recovered on Rat Island and that were also banded on their natal colonies in Puget Sound, lower Columbia River, Columbia Basin (Goose Island area) and San Francisco Bay. These movement patterns have implications for the spread of diseases by terns and suggest that terns move both long and short distances among breeding colonies, they move regularly during their lifetimes, and that the most common pattern of movement, between the lower Columbia River and Puget Sound, is the pattern observed for the spread of H5N1 HPAI virus among terns in the region. Note that these movement patterns only represent movement among breeding colonies and not non-breeding movements to southern localities like Mexico or California and are likely biased by locations where there is a higher probability of detection and documentation such as where active research and observation is occurring.