Birds

Macaws and parrots fly up and down mountains searching for fruiting trees; the resplendent quetzal and the three-wattle bell-birds fly to lowlands after breeding.  Ducks, ibises, herons, storks and other aquatic birds depart from the wetlands as the dry season advances. Even more impressive is the arrival of migratory birds. Warblers, vireos, thrushes, tanagers, flycatchers, and orioles, to name a few, arrive to Costa Rica from the temperate and boreal North America during August, and become more abundant during September-October.

Hummingbirds:

Costa Rica has around 50 species of hummingbird.  These birds are most often seen feeding from flowers, but they also eat insects. The volcano hummingbird (Pselasphorus flammulla) is the smallest one (weighing only 2 grams) and occurs in the highlands. The largest hummingbird, the violet sabrewing (Campylopterus hemileucurus) is about 15 cm, and easy to watch at the Caribbean lowlands. Two good places to watch several hummingbirds are Monteverde and Cerro de la Muerte.

Raptors:

The raptors are both powerful and beautiful birds. They are easy to see flying, or perching in the opne canopy, where they have good visibility to look for prey. If you are travelling away from the city, pay close attention to the electricity cables and trees close to the road, and you’ll probably see at least one raptor. These diurnal birds of prey include: hawks, kites, eagles (Fam. Accipitridae); falcons and caracaras (Fam. Falconidae);  the osprey (near the water);the Caracara (Polyborus plancus); the laughing falcon (that is a treat to hear) (Herpetotheres cachinnans); the peregrine falcon (Falco peregrinus) that sometimes can be seen at the parks in the city preying on doves; the roadside hawk (Buteo magnirostris) and the broad-winged hawk (Buteo platypterus).  Raptor migration is a “must see”.   Columns of hundreds of birds in the sky are an amazing scene.

Quetzal and trogons:

Trogons are colorful birds easy to watch in the lowlands; the quetzal is common in the highlands. The breeding season of the quetzals is from March to June in the highlands, and it makes them easy to watch because the males sing to attract females. After the mating season, these birds migrate to the lowlands following the fruiting patterns of the “aguacatillo” trees.

Endemic species

Source: http://www.angelfire.com/bc/gonebirding/endemics.html

There are more endemic species restricted to Costa Rica and western Panamá region:  10% of Costa Rica's avifauna is restricted to very limited ranges within the southern half of the Central American isthmus, which is an exceptionally high rate of endemism.

Birds Timeline: Quetzal breeding season: March-June  -  Raptor migration: late September to mid November on the Caribbean lowlands and highlands, and from early March to late May on both slopes

Sources: Stiles F.G., A F. Skutch. 1989. A Guide to the Birds of Costa Rica. Cornell University Press. 511 p.
Janzen, D.H. 1991. Historial Natural de Costa Rica.