The word survey always makes me feel like I should be asking the little critters about their TV preferences and views on the global economic situation, but instead I am monitoring their populations in Ann Arbor parks and natural areas. The survey is in its 15th year and the data volunteers collect is used to track populations over time (click for a species richness map).
You sign up for a route, which consists of several sites, where you go to listen at least once a month from March through June, for the types and amounts of frog and toad species calling. Temperatures have to be at least 45 degrees, without extreme wind or rain, or the anurans won't be calling. The survey is done after dark, based solely on sound. (The calls are unique and easily distinguishable, and they give you a CD to listen to ahead of time to familiarize yourself with the calls, but it's a shame I don't also see the cute froggies as well.) Since frogs (many of which are only the size of a thumbnail) have many diurnal predators, they wait to call until night.
Only male frogs call, as they are trying to attract a mate. You don't try to count the exact number of individuals calling, but assign a frequency code to each species you hear: 0=no calls, 1=more than one individual calling, but with no overlap in calls, 2=multiple individuals calling with overlap, or 3=a whole chorus calling so individual voices are not distinguishable.
Wood frogs and spring peepers are the earliest frogs calling in my area, and they both have a kind of "antifreeze" in their blood glucose that keeps them from freezing over winter. The wood frog only calls for maybe one to two weeks, whereas the spring peeper can continue through summer.
The frogs and toads in my area, in order from early to late calling, are:
- Wood frog (Rana sylvatica)
- Northern spring peeper (Pseudacris crucifer)
- Western Chorus Frog (Pseudacris triseriata triseriata)
- Blanchard's cricket frog (Acris crepitans blanchardi, rare)
- Northern leopard frog (Rana pipiens)
- Pickerel frog (Rana palustris)
- Gray tree frog (Eastern-Hyla versicolor and Cope's-Hyla chrysoscelis)
- Green frog (Rana clamitans melanota, one of my favorite calls, banjo-like)
- Bull frog (Rana catesbeiana)
- Eastern American toad (Bufo americanus, also present in a vernal pond outside my yard)
Thanks also for your well wishes in response to my previous post. I'm happy to say I'm feeling better and more alert now! Zog good! :)