How do you know when the birds are here? This is a challenging question at the start to every field season. The house wrens in Michigan spend their winters down in the southern United States and every year they arrive at a slightly different time depending on how the weather has been across the country.
Here is where citizen scientist efforts are particularly helpful to researchers like me. Cornell University runs the eBird program (http://ebird.org/content/ebird/) where birders across world can submit lists of any birds they see. Checking eBird every days lets me watch the migration in real time. Citizen scientist efforts like this are extremely useful for ornithologists like myself. There's no way I could hope to track the migration by myself! When house wrens are sighted in Michigan, I know they might show up at my field site any day. Based on the data so far, I expect them to be here by the beginning of next week!
eBird view of house wrens from March-Apr 19th. Purple squares show all the places where house wrens have been observed. The darker the purple, the more times house wrens were seen.