This is an article written by the Nature Conservancy Team of Washington DC, that spent several weeks at Samasati in 1998 to study the Samasati Biological Reserve’s bird population.
Let's begin with the forest floor, where there is always a lot of activity due to the constant changes of soil and where many insects, amphibians and other animals live. Here live the anteaters, the leaf tossers and some "soterreyes" or wrens. These are not very visible and are very timid, usually brown-colored. Some have very beautiful metallic blue hues. If you walk carefully, it is possible to see the Chestnut-Backed Antbird (Mynmeciza axsul), the Ocellated Antbird (Phaenostictus mcleannani) or the Bicolored Antbird (Hylophylax naevioides) following an ant path. Or you might see a Scaly-Throated Leaftosser (Sclerurus guatemalensis) turning over leaves on the ground in search of food. Other occasional visitors to the ground or under-forest are hawks or falcons that live in the trees and hunt snakes and lizards. For example, one can easily spot the Collared Forest Falcon (Micrastur semitorquatus).
In the middle layer of the forest you find the majority of the flowers and fruits, in addition to the insects, that are food for the birds. You can observe the curious and active hummingbirds, such as the Long-Billed Hermit (Phaethornis longirostris), the Bronze-Tailed Plumleteer (Chalybura urochrysia) or the White-Necked Jacobin (Florisuga mellivora) among others.
Other inhabitants of Samasati's forest and its surroundings are the Tanagers and the Trogons with their contrasting colors and beauty. In the mornings, you can observe, among others, the Slaty-Tailed Trogon (Trogon massena), the Violaceus Trogon (Trogon violaceus), the Red-Legged Honeycreeper (Cyanerpes cyaneus), the Blue-ray Tanager (Thraupis episcopus) . The Wood Creepers are one very interesting group of birds. You can see a number of them, from the small Wedge-Billed Wood Creeper (Glyphorhynchus spirurus) to the large Barred Wood Creeper (Dendrocolaptes sanctithomae). They scour the tree trunks in search of food; their colors blend very well with the surroundings, so that they are sometimes difficult to see.
In the upper layer or canopy you can see birds as beautiful and surprising as the ones deeper inside the forest, even though they are usually larger birds and more peculiar. Among the birds of prey that can be observed we find the Black Hawk Eagle (Spizaetus tyrannus), the White Hawk (Leucopternis albicollis), the Guaco (Herpetotheres cachinnans), the Laughing Falcon and the Mayestic King Vulture (Sarcoramphus papa). The Red Lored Parrot (Amazona autumnalis), and the Mealy Parrot (Amazona farinosa), the White Crowned Parrot (Pionus senilis), and the Brown Hooded Parrot (Pionopsitta haematotis). Toucans are a very common sight here. At Samasati we can observe the following kinds of Toucans: Keel-billed Toucan (Ramphastos sulfuratus), the Chestnut-Mandibled Toucan (Ramphastos swainsonii). You can also find the Collared Arcari (Pteroglossus torquatus) which eats eggs and birds from other nests. If you listen carefully you can hear the loud pecks of two large woodpeckers easily spotted here, the Lineated Woodpecker (Dryocopus lineatus) and the Pale-Billed Wood pecker (Campephilus guatemalensis).
Also, in Samasati one can observe (in all of its magnitude) the phenomena of (the) migration, the subject of study and admiration by scientists from around the world, in particular the migration of the Warblers and the birds of prey.
In the months between September and December, one can see up in the sky, highways made by hundreds and hundreds of birds of prey that come from North America to the tropical countries, in search of shelter and food, escaping the winter that ravages the north. Among the birds of prey that pass through Costa Rica you can see the Turkey Vultures (Cathartes aura), the Broad-Winged Hawk (Buteo platypterus), and the Swaison's Hawk (Buteo swainsoni).
Day by day you can observe these (relentless?) birds soaring the thermal flows of warm air on their way South. Some of them eventually remain in Costa Rica. In the forest, you can also begin to see movement with the arrival of the Warblers, such as the Yellow Warbler (Dendroica petechia), the Canada Warbler (Willsonia canadensis), the Chestnut-sided Warbler (Dendroica pensylvanica), and others such as the Wood Thrush (Hylocichla mustelina), the Eastern Kingbird (Tyranus tyranus) and the Purple Martin (Progne subis).
There are more birds to be observed in Samasati, see a list of the spotted birds above. A visit to this unique Biological Reserve is a must for lovers of bird watching.