Sunday, May 30, 2010

Introduced species

They DO count... only if they are well-established. OK, it may sound simple, but it can get complicated. Who determines when an introduced species is well-established depends on the local or regional birding or ornithologists associations based on sightings, historical records, population studies and so on... but sometimes, it can be obvious. Think about the Rock Pigeons. Most of the cities that I have visited until now holds a well-established population of this species. You may say that they are all around because of us and our food sources... but if suddenly all the people that deliberately feed them disappear, they will survive anyway. It was not included in the first edition of the Panama Birds fieldguide (back in the 70's) but now it is part of our official bird list. The populations of these birds are dynamic. There are many factors influencing the establishment of an introduced species to a region: number of individuals, habitat, adaptability, nest sites availability, competence with native or other introduced species. For instance, when I started birding (more than 15 years ago), the Saffron Finch was known only from an introduced population in the charming town of Gatun, in the Atlantic side of the Panama Canal. Back then, it was one of the main targets during the Atlantic CBC, because it was valid for the count, despite its tiny population. Since then, this species have spread along the isthmus and now is a very common resident in Panama City as well (also in some other localities, for example in Vacamonte, at the west side of the Canal). And what about the Tropical Mockingbird? First recorded in Panama City during the 30's, probably brought from Colombia as a popular cage bird due to its song, now is very hard to imagine a park or a neighborhood within Panama's main cities without them. Not only that, they have spread themselves all the way to Central America, being now not uncommon in some sites in Costa Rica. Sometimes, it is about chances of adaptability. In Panama, the urban niche was, more or less, available in order to be occupied by the House Sparrows when they arrived following its incredible expansion from North America. A pair or flocks of these birds is now a common sight at our streets, where they do not compete with any other sparrow species (contrary to what happened in other countries in South America where it competes with the Rufous-collared Sparrow). Many times, those introduced species are seen as invasor alliens that destroy the natural avifauna... but take into consideration that they simply are trying to survive and that usually we are responsible of their first occurrence after all. The ethical dilemmas abound in the literature about erradication methods, with tons of examples along the decades. Well, I think is better to let them alone with their lives... trying not to make worse the situation by introducing MORE species. What do you think?

1 comment:

  1. are you sure about the introduction of the saffron finch vs indigenous.