Are fire ants killing our Texas birds? Ask Alejandro Calixto and his team!

First it stings, then it throbs, then a little pustule forms. This pustule is a feature, made by bacteria the fire ant carries in its sting. These nasty ants came into the USA from southern South America with a cargo ship that landed in Mobile, Alabama in the 1930s, where they were soon after observed by our most famous ant biologist, Ed Wilson. Their formal name is Solenopsis invicta. They are an inconvenience all over Houston, punishing anyone who dares to wear sandals in the grass.

In nature they are much worse than an annoyance, for they have changed the landscape in ways that threaten many species, including the endangered Attwater’s prairie chicken. They do this in at least two ways: by directly attacking young birds and by competing with them for food resources. The team led by Alejandro Calixto of Texas A & M University is focusing on the latter question. Do fire ants eat the insects that prairie chicken chicks need to survive?

It may seem like an easy question to answer, but the actual process is anything but simple. First they have to know what baby prairie chickens eat. That they know – the diet includes insects of a certain rather small size. They also eat seeds, but the insects are a crucial source of protein. Then the researchers have to see if fire ants have an impact on those insects by comparing areas with and without fire ants. Finding an area without fire ants that is otherwise the same is tough. It requires baiting to remove the fire ants while hurting nothing else. The answers may vary with season, though the most crucial season is the one when the chicks are little. The answers may also vary with location across the Texas prairies that hold or once held prairie chickens.

So, if you are with me, we have an experimental design that has these factors: fire ant presence, season, and location. A balanced experimental design requires that all the variables be combined with all the other variables. For example, in each season all sites must be sampled, and each should have areas with and without fire ants. And the different blocks of treatments should be randomly interspersed. Don’t even get me started on the kinds of statistics needed to analyze this. I’m guessing my daughter, now an assistant professor at University of Memphis and teaching statistics, would be up to it! But first, the researchers have to do a phenomenal amount of work.

But we’re not done with experimental design, because those are the independent variables only. Now we need to think about the response variables. What data are going to be collected in all those habitats and seasons? (Yes, “data” is a plural, and the singular is “datum,” so now you know, use it correctly.) In this case, the researchers sample the insects in the community by sweep netting the vegetation to see what is out there for the chicks to eat. They put these sweep samples in bags to be taken back to the lab and analyzed for insect size and species. I don’t know what they do with the non-insects like the spiders and doodle bugs, but I bet they count them too. The other response variable is the numbers of fire ants in the area. This is the one I got to witness most specifically on a hot Friday, 3 June 2011, when the team let me tag along with them to the Texas City coastal prairies.

Even though fire ants seem to be everywhere, a researcher needs a good method of counting them that is consistent and repeatable from site to site, season to season. In this case it involved baits with hot dogs (see photo below). Not just any hot dog, but a certain brand (I forget which), that contains protein, fats, and sugars. I know Alejandro tried a lot of brands before finding just the right one. Fire ants that are not rearing babies only go for sugar to maintain the adults, while with babies, they go for the protein. I know this from some class labs I used to do that put out tuna or jelly to see which the ants preferred.

The team met early that Friday morning, right at the study site. Alejandro had a map of the area, and a plan for dividing up the sampling. They had been there before in other seasons. The plan involved both sweep netting the areas, and putting out hotdog baits, then counting the ants they attracted a few hours later. One important thing about a study like this is to do it blind. I don’t mean with your eyes covered, but in a way that means the person collecting the data does not know if it was an area that was baited or not. We scientists try hard to be unbiased, and even to avoid inadvertent bias, and this is one way we do that.

The researchers divided up. Besides the project leader, Alejandro Calixto, the team on that day included a local researcher, Gus Fowler, and two assistants based at Texas A & M entomology, my son, Daniel Mueller, and Joe Fihe. I tagged along with Alejandro, so I could learn about the project. It sure did make me miss field work. Walking from site to site, following the map and the GPS, then netting and baiting, leaving behind flags so we could find the baits again. I saw the damage from Hurricane Ike in the form of rubble still piled in the fields. I saw an eastern meadowlark singing away. Two caracaras had already made up their minds about each other, and mated right in front of us. We were just off Galveston Bay and could feel the warm, wet, sea breeze. Cattle also used the fields, and eyed us suspiciously, particularly when we were between them and their water source.

What are the answers? I can’t tell you, because this is an ongoing study. But it is this kind of careful, intensive work that will tell us what is important for this endangered bird, perhaps less spectacular as a physical specimen than for its flamboyant lekking behavior. So stay tuned, and look for what Calixto and his team discovers.

I’m having some photo issues, which is frustrating because I took all the photos myself, but they will be added in with modifications of the blog.

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About Joan E. Strassmann

Evolutionary biologist, studies social behavior in insects & microbes, interested in education, travel, birds, tropics, nature, food; biology professor at Washington University in St. Louis
This entry was posted in Biology, Environment, Insects, Natural areas and tagged . Bookmark the permalink.

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