BIRDS AND BEYOND

Listen to the sounds of spring

By Claire Curry | Published Thursday, March 18, 2010

“Official” spring, the equinox, is getting closer and closer, but already we have a wide variety of spring singers creating a wonderful soundtrack. Most of our early singers are birds and frogs (the insect chorus will get louder as the season progresses). I’m going to talk about why they are singing and what you can listen for at this time of year.

Animals communicate through song. The singer is sending a message to a variety of listeners – other males, females and even potential predators.

A frog may want its fellow frogs to hear its booming voice, but predators can hear it, too. A colorful, singing bird is advertising its vigor, but sitting still and making noise on a conspicuous perch makes it more vulnerable to predators. Thus, all communications can be hijacked.

Indeed, when we look for a bird after hearing it sing, we are effectually hijacking its message for another purpose. The bird isn’t singing for our benefit, but we take advantage of the sound to get a good look at the beautiful cardinal or bouncing wren. Predators just take it a step further and eat it.

So, to avoid being eaten, a creature could just stop singing, but it has a message for potential rivals and mates. A distinctive song signals to a female that the singer is a member of its own species. It would be a waste of energy for a female cardinal to track down a singing wren, so cardinals that can recognize their own song will leave more offspring. Those offspring will likely inherit the parents’ ability to learn their own species’ song.

Likewise, there is no point in a male wren attacking a male cardinal in its territory; they aren’t competing for similar foods or for the same females.

Different animals use cues to decide if the singer might be a worthwhile mate. In frogs, for example, the pitch of the song depends on body size. A bigger frog can have a lower-pitched song due to the physics of sound production. If a female prefers a larger mate (perhaps because her offspring would be bigger and those offspring might do better battling for potential mates in the future), then she can make a choice just by listening to the various males at a pond.

Different birds may prefer songs that are more varied, more similar to the ones they grew up learning or that are sung for longer periods of time.

Although we’re waiting for the first green sprouts of spring and associate singing birds with that time, they actually begin their breeding seasons based on daylight cues. So, after a certain time of year, birds may sing whenever the daily conditions are good (a warm or sunny day).

Getting started singing earlier than other members of their species may snag them a good territory and partner earlier than the neighbors. In fact, in juncos (a winter bird species here in Texas), males winter farther north and migrate north earlier to get choice territories. However, if they go too soon, they may not find any food. It’s a trade-off between getting a head start on reproduction versus finding food.

Likewise for frogs, breeding early may give a head start (the tadpoles will get bigger before the others, and the frog might get to lay more eggs later, too), but there is the possibility of a late deep freeze killing your tadpoles or their food sources.

Frogs typically start singing based on how wet it is and how warm it is, so they are particularly vulnerable to unusual weather. A warm, wet period followed by a late freeze could cause more of them to breed too early.

Thus, all aspects of singing have some trade-offs involved. Sing too much or too conspicuously and you may get eaten. Don’t sing, and you won’t find a mate. Start singing and breeding too early and you might not find enough food for your babies, but start too late and you won’t even get a good territory or leave as many young’uns behind.

These opposing pressures contribute to the ultimate reasons why the birds and frogs are singing now, and not a few months earlier or later. Variation in the genetic basis for these timings and traits means that most individuals will start at the “best” time, but a few will start earlier or later.

What kind of creatures will you find outside right now? Some industrious amphibians will be singing in 40-degree weather, but all we’ve heard so far are the Strecker’s Chorus-Frogs, which individually make peeping sounds. When you get the whole chorus going, it’s a cacophony of peeps, near and far, loud and soft.

Northern Cricket Frogs are also very common. Their song is a clicky noise, like a marble being rolled in a glass jar. I remember their song by calling them the “Northern Clicky Frog.” Woodhouse’s Toads and narrowmouth toads will also be singing soon, with long mournful bleats of “mmrrrrreeeeeah.”

With birds, many resident species are now singing. Cardinals, titmice, Carolina and Bewick’s Wrens and Red-winged Blackbirds are all beginning to sing, especially in the morning on warm days.

You might hear the sharp calls of Downy Woodpeckers and the coughing calls of Red-bellied Woodpeckers, too. Although we don’t call their vocalizations songs usually, a song doesn’t have to be melodious to qualify. The woodpecker songs are still advertising the bird’s territory and availability.

The intricacy and beauty of animal sounds is amazing, even more so when you consider the fact that they are talking to each other. So, keep your ears open for the glorious sounds of spring. You never know what wonders you will hear.

The next monthly field trip to the Lyndon B. Johnson National Grasslands is Wednesday, April 7. We will leave at 9 a.m. from the Forest Service District Office in Decatur. For information, contact Mary Curry (see below) or the Forest Service District Office, (940) 627-5475.

Claire and Mary Curry are nature enthusiasts based in Greenwood and can be reached by e-mail at larksparrow@eeclaire.com.

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