Heat Wave Science Notes

One of the more entertaining things I do is volunteer at the Trinity River Audubon Center in Dallas.  It's a beautiful place -- the more so considering that it's a Brownfield Remediation site (The Environmental Protection Agency defines a Brownfield as “a property on which expansion, redevelopment, or reuse may be complicated by the presence or potential presence of a hazardous substance, pollutant, or contaminant” -- and as it was the site of an illegal landfill, all of the above applied.)  Over the three years that I've been involved, I've seen the landscape change from the fairly raw-looking land (the center had just opened) to an area that looks like a preserved wild area to the untrained eye.

To the trained eye (such as a Texas Master Naturalist like myself) it's obvious that this is reclaimed land.  There's a lot of invasive plants, but we're seeing a rebound in native plant species and native wildlife.  Then came drought and the heat wave.

I teach environmental science to kids -- talking about adaptations and turtles (an easy species to love), taking them on turtle counting hikes and then talking about bugs (not quite so easy to love) and taking them on bug hikes.  One of the strategies to get them less afraid of "bugs" (which includes any creepy crawly thing and not just insects or insects of the order Hemiptera) is to take a hike with them and engage them in a game of "nature bingo."

I try to make the bingo squares something that everyone find easily.  On the list that I made this spring, I put a number of butterflies including "yellow butterfly" (the sulfurs, Phoebis sp) and "white butterfly" (Pieris rapae) as well Tiger Swallowtail, Pipevine butterfly, and Monarch.  The game was a hit with the kids and things rolled along pretty much as expected until one week they didn't find any butterflies at all.

That was interesting.  Then a second group made the same report.  And a third.  I decided to investigate.

I took a group of kids off to specifically look for butterflies one morning.  We walked for about 40 minutes in areas where I knew butterflies were common, but we only found two of them.  TRAC has its own butterfly garden with native plants and water to support butterflies.  It's a good spot to hang out to take butterfly pictures, so I headed there next.  The plants were in bloom, but there weren't any butterflies visiting them, though the bees were enjoying them.

So were they really gone, or were they somewhere else?  In spite of the hundred degree heat and drought conditions, I took an afternoon hike of the distant trails at TRAC.   During the hour's trek I only saw two sulfur butterflies -- and another butterfly that landed briefly and appeared to be one of the Nymphalinae.

So where are they?  When I asked, nobody else had seen butterflies recently -- but they hadn't stopped to wonder if that was peculiar.  Someone suggested that it was "too hot for them to fly," so I tested that idea by hiking at 8 am and 8 pm.   

There are plenty of nectar sources around.  There's water.  There's birds, of course, but surely they wouldn't have eaten every single one.  There's lots of host plants around, including the Partridge Pea (Chamaecrista cinerea.)  These particular butterflies should breed all summer long -- not in a single group and die out.

One thought that has been troubling me about the heat wave and the drought is that it is causing certain plants to die off and animal populations are shifting.  What happens when the drought ends?