[vernalpool] Re: rain before, not during: Big Night uncertainty

Thanks so much for the responses; hearing about others' experiences is a big help.

Bryan, I share your concerns about the term "Big Night" but for social marketing purposes, it's a good hook for dragging volunteers from their warm homes onto dark, cold, rainy roads! Seriously, in presentations and outreach materials, I do explain that movement isn't limited to only one big migration night, but that conditions may be favorable for multiple movements over the course of the season.

Thanks again,
Laura

--- In vernalpool@yahoogroups.com, Bryan Windmiller <bwindmiller@...> wrote:
>
> Hi Laura,
>
> In my experience, I have seen substantial migrations on nights when it has
> not been raining. My own sense over the years is that the threshold for
> triggering migrations by the early spring-breeding amphibians drops over the
> course of the potential breeding season.
>
> So, for example here in NE Mass., in the past 23 years I think that the
> earliest date on which I have seen a fairly large scale migration event by
> Ambystoma spp., wood frogs, and spring peepers was on March 9. That early
> in the season, the conditions have to be REALLY good - warm, lots of rain,
> etc.
>
> Much earlier in the season (in say late February, around here) there will be
> essentially no migration no matter how good the conditions are - heavy rain,
> temps in the 50's, fully thawed ground etc. - I *think* that is because the
> amphibians have what I refer to as a gated response - they are, I believe,
> inhibited from migrating before a certain time of year, based on their
> internal photoperiod, no matter how good the conditions.
>
> Alternatively, in springs in which good conditions don't materialize until
> late in the season, i.e. there are no good rainy nights until early April,
> the threshold for migration is much lower and you will often see large
> migrations when the ground is just wet even if not raining at night.
>
> Anyway, that's my sense based on my experiences.
>
> One more pet soapbox - I always cringe at the use of "big night" as a term.
> Having conducted drift fence and minnow trap surveys at dozens of pools
> over many years, I have learned that there are, in most years, a number of
> nights on which large proportions of a given population of Ambystoma or wood
> frogs immigrate to their pools. More often than not there is no single "big
> night".
>
> Best of wishes with your work,
> Bryan
>
>
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>