The movement of species typical of the tropical dry forests of Guanacaste into the Central Valley continues at a rapid pace. In particular is the explosive expansion of the white-winged dove with this conspicuous species increasing its numbers rapidly. In some areas around Heredia where it did not occur at all five years ago and still with just a few two years ago, it is now omnipresent with flocks as large as 40 or 50 in particularly favorable conditions.
The white-winged dove is easy to identify and observe. It is a medium-size dove a little smaller than a domestic pigeon with white on the wings and tail that flashes conspicuously in flight and is visible as the birds moves around on the ground looking for seeds and fallen fruit. It also sits on low trees and phone wires where it is even more conspicuous.
Nests are flimsy platforms usually in a tree or bush with 1 or 2 white eggs.
In areas where the white-winged dove has increased the much smaller Inca dove seems to decrease. The Inca dove is itself a relatively recent arrival, colonizing the Central Valley only in the 1970s.
Other species typical of Guanacaste have also increased in the western Central Valley and moved east towards Cartago. These include white-fronted parrot, rufous-naped wren, rose-throated becard, lesser ground-cuckoo, crested caracara, and melodious blackbird. The latter had its first records in Guanacaste in the late 1980s, and continued to Panamá on both slopes since. These species have all come from the west and north with less possibility of colonizing the Central Valley from the east, though the black Caribbean race of the variable seedeater has recently reached Santo Domingo de Heredia.
These sudden changes are not easy to explain, as habitats have not changed much in the Central Valley in recent years despite development and increased human encroachment on agricultural areas. Most of the areas lost to industrial and residential development have been the same for 250 years or more, such as coffee plantations. Speculation that climate change might contribute have been raised, but the small changes in temperature in tropical areas are far from changing the habitats that given species of birds frequent.
Observations of birds that are genuinely rare have also increased, though this is probably the result of more bird watchers than changes in the avian population. More Costa Ricans are now looking at birds. The concept of long-distance vagrancy of migratory birds is well-known in northern countries with knowledge best developed in Britain and California. Three species of ducks previously unknown to Costa Rica were found in the northern winter of 2011-2012. These were in relatively obscure sites. The large number of ecotourists who have come here over the last 20 years have tended to go to the same well-known places.
A better example of this phenomenon is the tropical mockingbird, where the first record was a pair frequenting the center of the town of Siquirres in the Caribbean lowlands, most definitely not a tourist destination. The species is now cropping up elsewhere too.
Amateurs can contribute to process, with better books now available and better access to more areas all the time.
It’s the start of the rainy season again and that means the national bird is singing furiously while settling matters of territory and mates. The clay-colored thrush or yigüirro for a few weeks goes from common but relatively inconspicuous to singing everywhere.
This brown thrush is very much the ecological equivalent of the turdus thrushes familiar to Europeans and North Americans like the song thrush and American robin. It is an omnivorous feeder well adapted to human-altered habitats.
An article last year described and provided links to the various songs that the yigüirro uses.