By Richard Jerome, Cataloging Intern, Field Book Project
Invasive species have become a serious environmental problem of late. As someone who enjoys swimming in upstate New York lakes, I often have to deal with one such species—zebra mussels. Not only are their shells so sharp that you have to wear water shoes when swimming, zebra mussels can cause more serious problems like the clogging of water filtration pipes and suffocation of other native species. All across New York people try hard to keep these animals away because it seems like once they enter a lake or waterway, it is impossible to get rid of them.
After doing a little research I’ve found that there does not seem to be a solid consensus about exactly how zebra mussels, or many other invasive species, enter new areas. This may be because invasive species are rarely observed at their point of entry—they just tend to start showing up. Of course it is a different story when humans purposely introduce a foreign species for a reason such as pest control, but generally the question of invasive species’ point of entry can be a tricky one.
While I was cataloging a field notebook of Alexander Wetmore, ornithologist and 6th Secretary of the Smithsonian, I came across an amusing anecdote in which, for one species, he found an answer. Wetmore had been observing mockingbirds (more specifically Mimus gilvus tolimensis) in the Canal Zone of Panama during 1956 and wondering how they got there. One night his neighbor E. J. Husted told him a story. Wetmore recounted it in his journal:
Between September and November, 1935 about 200 live mockingbirds in cages were brought from Colombia on a ship that docked at Pier 18 in Balboa, and were disembarked on a baggage truck that Mr. Husted was handling. The birds were intended for sale in the market in Panama, but the authorities demanded a dollar import duty on each bird. As the importer had expected to sell them at $1.50 each he became disgusted, opened the cages, and released the entire lot at Pier 18. [Mr. Husted’s] account is definite in detail and I have no doubt that this is the explanation of the establishment of the species in the Canal Zone.
The story is not verified by anyone else, but Wetmore has no problem accepting this as the likely solution to his question. If true, it shows how new species can be introduced in surprisingly strange and unpredictable ways. While mockingbirds may not be considered as destructive or as unwanted as zebra mussels, it is hard to imagine anyone being so careless with a foreign species today. Wetmore himself was not troubled to learn of these events; he just seemed satisfied to be able to find an answer. Stories like this are the kind of gems that pop up over and over when reading through old field books. We may fight hard to stop the introduction of non-native species to new areas today, but back in 1956 Wetmore heard this account and his reaction was simply, “Of course! Now it all makes sense.”
For more on Alexander Wetmore and field work with invasive species check out the following related blog post: The Dangers of Bunny Rabbits