Climatic Extremes Drive Abrupt Shifts in the Distribution of Franklin’s Gull

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Franklin’s Gull (Leucophaeus pipixcan) nests in marshes, primarily in the Great Plains, Great Basin, and Intermountain West. On the periphery of the range, its nesting was first documented in Lower Klamath National Wildlife Refuge in 1989, but numbers remained very low through the early 1990s. After first spiking in the Klamath Basin in 2003, numbers generally were modest through 2013, then increased greatly (many hundreds to low thousands) in most years from 2014 to 2022, but dropped sharply in 2023. In 2012, observers counted 100 nests at Lower Klamath, and other indirect evidence implied nesting at or near Lower Klamath and Tule Lake national wildlife refuges from 1994 to 2022. These changes are part of a broader pattern of increases in adjacent regions. Colonization of the Klamath Basin followed displacement of gulls from flooded marshes at Great Salt Lake and elsewhere in the mid-1980s, but from the early 1980s onward likely was facilitated by local management that greatly extended early-successional marshes. Since 2003, spikes in Franklin’s Gull numbers in the Klamath Basin have largely coincided with extended drought in areas with the nearest large colonies in Utah, Idaho, and southeastern Oregon. Rangewide population trends are poorly documented and difficult to track because the breeding marshes’ dynamism drives variation in colony sizes and locations. As climate warming increases the magnitude and frequency of droughts and floods, more accurate monitoring of population trends in Franklin’s Gull is needed. Meanwhile, anecdotal observations may give early warnings of population fluctuations and range shifts.