Ibis in the Estuary

I was out on my first day of walking.  I’d just left a path cutting through summer pasture lands along the west side of the Lac de Grand-Lieu.  The lake is barely 15 miles from Nantes to the southwest.  Winter rains turn it into the largest lake in France.  In the summer, though, with less rainfall and the local water authority releasing water into the Loire, the lake surface is cut in half, opening up pastures where local farmers graze dairy and beef cattle.  I was getting bearings before going off in a new direction and I noticed three birders coming up the path, binoculars around their necks.  We exchanged “bonjours” and one asked if I’d happened to see any ibis on my walk.  I said no, that with all the cows I’d mostly had my head down concentrating on where I put my feet.  I think they smiled.

I knew just barely that Lac de Grand-Lieu was an important stopover for birds on a major north-south flyway.  I though I might see herons or storks, but not this bird from Egyptian mythology.

Then, a week later, I saw two of them.  By now I was quite a ways from the Lake, maybe 25 miles to the northwest.  I was out on a day hike looking, not for birds, but for the Menhir de Pierre Bonde.  According to the map, it was supposed to be in a marshy field a mile or so south of the Loire.  Menhirs are sprinkled all over France.  Many, if not most, are like this one, large stones usually standing upright, frequently alone.

  The fact that they have no geologic reason for being where they are means, most likely, that an ancient people put them there.  The mystery is how and why.  Maybe, like England’s Stonehenge, they had some ceremonial function.  Here, the menhir stood out, orange lichens coloring the top, rising up in the middle of someone’s private, fenced-off field.  

And there, just off to the right of the stone, were the two ibis.  These were sacred ibis with large white bodies, black tail feather, black feet, and a black head which seemed to have been compressed by powerful forces to squeeze out a long, downwardly-curved, black beak.

 

Later, at the bed & breakfast where I was staying, thinking I had a rare sighting, I mentioned it to the host.  Oh, she said, they aren’t at all rare, in fact, she added, they’re considered an invasive species.  I read later that a zoo in the area had imported the birds sometime in the 70s.  At some point, a few birds escaped and began to reproduce.  A 2006 census counted 1,700 pairs and a total of about 5,000. 

Concerns had been growing about the possible consequences of this new bird.  It was said that ibis were eating the eggs and chicks of other birds like herons and terns.  More, they might be carrying diseases picked up from feeding on waste dumps.  As a result the government began an eradication program, shooting birds and piercing eggs in the nests.  It was successful.  Another census in 2013 found the ibis population had been cut by nearly 80 percent.

Is it possible that this was all a mistake?  That this invasive species isn’t necessarily harmful and might even be beneficial?  This was the conclusion of an article published two years ago based on more than 10 years of analysis of the ibis diet.  All of the data came from birds in the local department of Loire-Atlantique.  Loïc Marion, a researcher at the University of Rennes, found no evidence that ibis eat eggs or chicks of other birds, nor than they eat more than incidentally from waste dumps.  On the other hand, he found than more than 40 percent of the birds’ diet consists of Louisiana crayfish, itself an invasive species that has infested the Lac de Grand-Lieu.

There’s probably an important lesson in this.  Certainly some invasive species create serious problems.  Besides the Louisiana crayfish, nutria and catfish are also causing headaches along the Loire.  But, as the case of the ibis suggests, simply saying a species is invasive isn’t enough to establish that it’s really a problem.  In a world where so many plants and animals are already dispersed and intermixed, some amount of careful analysis is needed before deciding on the kind of eradication program used against the ibis.  Happily, for the moment at least, it’s still possible to happen on a pair in a field somewhere along the estuary.