Last Sunday my friend Pancho invited some of us at the Reserve to visit his family home in the mountains just northeast of Jalpan, and a nearby cave. To reach the cave we had to hike up a steep slope. As we approached the mountain crest vegetation changed from low, spiny scrub to a regular forest with attractively spreading oak trees interspersed with an unusual number of Mexican Walnuts (Juglans mollis). The Reserve protects the ridge forest, else so close to town firewood gatherers surely would have decimated it by now.
Even at that only modestly high elevation a coolish, fresh breeze filtered between the oaks' black trunks, light was sharper and more contrasty than usual, and even sounds were crisper and clearer than usual. At the top we heard it. If your PC can handle MP3 audio files (Windows Media Player), you can hear it, too, at http://web2.uwindsor.ca/courses/biology/dmennill/CostaRica/THTI.mp3.
That's a good audio file, showing exactly what the sound was like: Background birdsong framing a shimmering, penetrating, clear, hollow and haunting monotonal whistle. It was the call of the Thicket Tinamou, CRYPTURELLUS CINNAMOMEUS. You can see a painting of a female Thicket Tinamou at the bottom of http://www.1-costaricalink.com/costa_rica_fauna/thicket_tinamou.htm.
Tinamous are strictly neotropical birds -- not found outside the tropics, and nowhere but in the Americas. They have their own ORDER, which is pretty impressive, since only about 30 bird orders are recognized, and most birds most people know belong to just one order, that of the "perching birds." Taxonomically, tinamous are as different from other birds as doves are from parrots and hummingbirds from seagulls -- they're all in their own orders.
Tinamous are large-bodied, almost tailless birds with slender necks and small heads, maybe 30% larger than a bobwhite. They look a bit like emus, but smaller. They fly but prefer to walk or run, and they're secretive. Their nests are scrapes on the ground, and the birds eat vegetable matter and small invertebrates. One female may lay for several males, and more than one female may lay eggs in the same nest.
I've heard tinamous in out-of-the-way places throughout my life but I've never clearly seen one. A Nahuatl-speaking friend once showed me how to call a Thicket Tinamou, and I can make them come closer with my whistle, but, still, I've never identified one with 100% certainty.
Being such plump-bodied birds, country folks have long hunted them. Their occuring on the Reserve-protected ridge is a testament of the Reserve's efforts.