The bird community keeps changing, almost certainly in part because the experimental farm is now a patchwork of growing forest, grazed pasture, and weedy regrowth.
We first censused birds at our site in 1994, a year after removing cattle from the amphitheater and planting the experiment Bloques'93. The pasture was dominated by one species of seed-eating finch. Around the spring at the foot of the slope were a few trees that attracted a half-dozen kinds of fruit-eating tanagers. One kind of hummingbird occasionally flitted by.
We established a permanent bird-census site near the spring and found a comparable site, also surrounded by pasture, on a neighbor's farm as a control. Over all these years, that site is still surrounded by pasture, so it continues to serve as a control. We have re-censused the birds approximately every four years. The kinds of birds in both sites have changed. We see some kinds that used to inhabitat lowland areas. Changes in the kinds of plants that survive and fruit at our altitude also suggest that climate change may be playing a role.
However, it is clear that the patchwork of maturing trees in our experimental plots scattered across the farm is offering a more complex environment and more varied resources than the overgrazed pasture did during the 70s, 80s, and early 90s. We see birds characteristic of forest now, such as guans and toucans. We now have a wide diversity of hummingbirds.
These data are difficult to publish because many factors could explain the changes. In the future, we will construct a page of our data for interested parties.