More mature forest means more birds. The copious number of individual birds, a good number of species, and near constant avian action in second growth can trick us into viewing edge habitats as the best places to bird. While the thick, successional growth at the edge of rainforest does host a number of species, including several canopy birds, mature forest still hosts more. Yes, bird the edge, but don’t neglect those long quiet walks inside the forest because that’s where you need to go for the biggest mixed flocks, most of the uncommon, rare, and spectacular species, and a host of peculiar understory birds.
Many understory species are especially dependent on healthy, mature forest probably because they have become adapted to living in a dim, shaded environment that hosts a complex, structured matrix of vines, small palms, and other understory plants. Since they share that dark maze of bushes, heliconias, and shade plants with various snakes, frogs, bugs, and other life forms that compete with, flee from, and try to eat each other, most of the understory birds are also naturally rare. We could also just as well say that they live at natural, very low densities and this is why we can walk on a trail for some time and find very few birds. The other reasons why we find so few birds in the forest interior is because they need to keep their presence on a serious down-low to avoid being noticed by predators, and because several prefer to forage in mixed flocks (another, additional means of avoiding depredation). At least that means that if you find the mixed flock, you also find a bunch of those shy understory birds.
I was reminded of these factors during recent birding/guiding at Quebrada Gonzalez in Braulio Carrillo National Park, and in the buffer zone at El Tapir. As is typical for these sites, we did find a few Checker-throated Antwrens and some other understory species that were foraging with them while walking on the trails. The antwrens give themselves away with a sharp alarm call or by giving their song; a short series of high-pitched, easy to ignore notes. While they forage in dead leaves, other birds also give quiet calls or reveal their presence by shaking a leaf or two. The whole thing is always a quiet, seriously inconspicuous endeavor and because of that, you can bet there are more birds out there, just staying out of sight. While watching the antwrens, we also heard Streak-crowned Antvireo, and saw Wedge-billed and Spotted Woodcreepers. In such flocks, other typical species include White-flanked Antwren, Buff-throated Foliage-gleaner, and Ruddy-tailed and Sulphur-rumped Flycatchers.
The hyper Tawny-faced Gntawren is usually also present, foraging near the ground, all the while looking very much like some out of place Asian tailorbird species.
Since other, rarer species are also possible, it’s worth it to stick with that flock as long as you can. But don’t leave the trail because there are other things lying in wait on the forest floor.
This nice sized Fer-de-Lance was a reminder of that possibility. Since it was next to the trail, it was easy to see and even easier to avoid. If this venomous snake sits in the leaf litter, you probably won’t see it. Although the chances of stepping on one after leaving the trail are slim, I would rather eliminate even that small chance by keeping to the trail.
Other cool understory species include antbirds, leaftossers, and grail birds of the understory like Black-crowned Antpitta and the R.V. Ground-Cuckoo. Although we did find a random Bicolored Antbird, try as we did, the gnatpitta and ground-cuckoo were both elusive along with the antswarms that act as the most likely situations to find such megas. However, before getting rained out in the afternoon, we did manage to connect with close views of a cool Northern Schiffornis.
After this odd brown bird came in, it opened and closed its mouth and sort of swayed back and forth.
Maybe the ground-cuckoo will show next time. You never know when it will happen and this is why a careful, quiet walk in mature forest is essential when birding in Costa Rica.