Question: Waiting our tern?

Caspian Tern is commonly seen along the Lake Erie shoreline in northwest Ohio during the warmer months. But this year, at least, it showed up later here than it did farther east along the lake. Photo by Kenn Kaufman.

April 12:  Every day for the last 10 days, my birding time has included visits to hotspots on the Lake Erie shoreline in Lucas or Ottawa counties, n.w. Ohio.  I've been expecting to see Caspian Tern any day, and I finally did see one on April 11. 

Looking at the data on eBird, no one had the species much earlier in this area. (Tom Bartlett saw one on Sandusky Bay on April 10, and Ethan Kistler and Jeremy Ross both saw singles on Ottawa NWR on April 12.)  But just a little farther east along the Lake Erie shoreline, from Lorain to Cleveland, there were reports of singles and small flocks several days earlier -- going back almost 2 weeks, to March 28th.  Why would Caspian Terns show up earlier on that part of the lake?

The western basin of Lake Erie displays some notable differences in birdlife from the rest of the lake, with some deep-water birds like scoters being much more common farther east.  But I can't see why this would affect the timing of something like Caspian Tern.  Is this just a fluke, something that just happened this year, or is it consistent?  I'll have to see if I can find any data from past years -- or just try to document the timing carefully next year as well.