Posted by: "Dan Dugan"
> Interesting, when I'm able to contact her I'll pass your comment on.
> This is only about one species that she says behaves differently from
> others re traffic noise.
It would be unusual compared to our chorus frogs. The Mountain Chorus
Frog, for instance, I only have recordings of them calling set off by
traffic. I know they must call at other times as they have been around
far longer than cars, but several years of special trips to record them
have had that result. Far more likely to find them calling with traffic.
Really annoying as it's the better part of a tank of gas to make the trip.
I would say a fair high percentage of the sites for treefrogs and chorus
frogs I've found have been found because they started calling as I
passed in the truck. Standard practice to drive slowly down roads at
night with the windows open. You'll find ten times as many spots as you
managed to see in daylight.
> I would think so, if the frogs were alerting to danger by sensing the
> low frequencies. If the calling behavior change was due to masking,
> however, maybe not. Then again, maybe the frogs could recognize the
> point source of the little speaker and tune it out, but the same
> sound level of more diffuse traffic noise had a different effect.
> Lots of variables.
My impression is not that the frogs are alerting to danger, far from it.
If they alert to danger, the first thing they do is shut up, they are
instead responding to the traffic sound like to a rival with calling. Or
just a fellow frog calling in the pond might be a more likely
explanation. One should not interpret how they think about it from how
we would think about it. That's a big error in a lot of these studies.
One interesting thing is the heavy engine sounds will set them off, but
one of the "thumper" cars generally won't unless it also has heavy
engine sounds. Frogs also set off to the sound of lugged tires
sometimes. Exactly which component of "traffic sound" is key could be
the subject of a interesting study.
Frogs of most species are group callers, that's why we talk about
recording frog choruses. They depend on having a group calling to get
the females in. A few frogs calling rarely get females to come in. I've
observed this a lot with the resident Gray Treefrogs at our house. Frogs
may be using the traffic noise to increase their apparent numbers when
they don't have quite enough males willing to call. In which case
breeding success may be improved by traffic. I know with the Mountain
Chorus Frogs I have found plenty of amplexed pairs and fresh eggs under
the situation where they only called when a car passed. A lot more study
of the females and just exactly what brings them to the water is needed.
Most breeding frog studies are really just of the calling males.
Even a small speaker can set off males to calling, if it's close to them
and playing the right call. (small speakers don't carry very far) But as
I understand it they were trying to play back recorded traffic which is
a different thing. They needed to put out much more sound energy.
Always, before drawing conclusions about playback effects of no response
go out to the frog position and listen to what's getting to you from the
speaker. If you want to be more scientific you could even take a sound
meter out and measure the level from the speaker.
Think about this, I've measured sound levels from frogs. A frog that
measures 80dBA or so at 6 feet may be calling at 125dBA or more at the
frog (much harder to measure at the frog). Not many small speakers in
playback are putting out even 80dBA let alone 125dBA. And people are
using playback and expecting something that's not their call to get a
response when it's hundreds of feet across the pond.
Interactions of male frogs in vocalization are clearly local most of the
time. Though I have observed male bird voiced treefrogs holding calling
competitions across a large pond. Call, then clearly listen to the other
frog, adjust aim and call at the other frog, back and forth. But then
bird voiced treefrogs are the stun guns of treefrogs here. They call
from the bush at head height and will call without regard to your ear
being nearby. A painful experience.
Also many of these frogs will respond to even crude imitation "calls"
we might make. The distribution of the Pine Barrens Treefrog in Florida
and Alabama is known almost entirely from folks out making such
imitations. Their calling sequence and timing is such that survey
depending entirely on their natural calling will miss most of them.
Note often I can drive the truck up next to some water and observe the
frogs from the truck without them being upset. If I walk up to the same
water they shut up and take cover. Often long before I'm at all close.
Only when large numbers are wildly excited in calling can you easily
approach them.
It's not as simple as cars are bad. Though some researchers seem to
start with that as a given. Patterns emerge if you spend enough time out
there paying attention. Then the effects of those patterns take even
more study. Keep a open mind to what you find. And try thinking like a frog=
.
Walt
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