Bird diversity research | Cloudbridge Nature Reserve in Costa Rica

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Avifauna Diversity

A research project at Cloubridge Nature Reserve in Costa Rica
See also Bird Sightings

"Human life is not purposeless. Rather, the moments of intense pleasure we experience in our encounters with nature may well justify our existence."
Alexander Skutch, Ornithologist

Summary:

Purpose

Method
Results & interpretation

Resplendent quetzal (Pharomachrus mocinno)

Avifauna at Cloudbridge
by Nathan Marcy

Purpose

The two objectives of this study were:

to make a thorough survey of bird life at Cloudbridge, and
to look for differences in the bird communities within different habitats in the Reserve.

Method

Observations were made during September and October 2004 at six sites, chosen to reflect the diversity of habitat types at Cloudbridge. They included primary cloudforest and older secondary forest, young secondary forest and thicket, succesional area composed of dense, low shrubbery, and mature riparian forest.

Five observation sessions were conducted at each site. Each session lasted one hour, and took place between 06:00 and 09:00. The data collected were as follows:

A list of all bird species observed within the site area during the hour.
As accurately as possible, the number of individuals of each species present.
A description of the location within the vegetation where each species is observed (from ground to canopy, where present).
When possible, a description of the preferred habitat and behavior of the birds.

Also, all species that were observed on the property (whether during observation sessions or not) are included in a master list (see cloudbridge.org/birds.htm).

The results of this study have been compiled into a set of lists and charts which demonstrate the abundance and diversity of Costa Rica cloudforest avifauna in different habitats. The following represents a summary and interpretation of the findings.

Results and interpretation

Site 1: At the intersection of the Cloudbridge Ridge Trail and the main Chirripo trail. This site includes primary cloudforest (on the south side of the Chirripo trail) and older secondary forest (on the north side of the trail).

Of the six sites, this one had the greatest abundance of birds, the second highest diversity of species, and the most endemic species. The high abundance value is mostly due to mixed flocks of tanagers and warblers. Such flocks were strikingly larger here than at other sites, and seemed to appear more frequently as well. The Common Bush-tanager (pictured) was especially numerous and often dominated the mixed flocks. Some of the other species most common at Site 1, like the Spangled-cheeked Tanager, Black-cheeked Warbler, and Flame-throated Warbler were rare or absent at all other sites. Species like these must favor the relatively high elevation of this site, its unique primary forest habitat, or a combination of both. With its towering trees, this site had the greatest vertical diversity of habitat, and many bird species showed strong preferences for particular strata. Most of the species "endemic" to Site 1 favored the upper canopy. The Long-tailed Silky Flycatcher is especially notable for this; it was always seen at the extreme highest points of trees.

Site 2: At the forest edge on the Ridge Trail. Vegetation was young secondary forest and thicket.

As at Site 1, the Common Bush-tanager was the most abundant species at Site 2. The composition of mixed flocks here was quite different, however, with Silver-throated Tanagers (picture at right) and Slate-throated Redstarts in the place of Spangled-cheeked Tanagers and Black-throated Warblers. Like Site 1, this site hosted a high diversity of the insectivorous woodcreepers and foliage-gleaners. Also well represented were the larger fruit-eating species, such as the Emerald Toucanet, Red-headed Barbet, Sulfur-winged Parakeet, and Black Guan.

Site 3: In the upper meadow along the Ridge Trail, approximately 100 meters above the main trail. Vegetation was early succesional, almost entirely composed of dense, low shrubbery.

Birds were scarce at Site 3; it had the lowest values for both abundance and diversity. Fewer than half as many species were observed here than at any other site. This is probably because Site 3 has the least vegetation, the most homogenous vegetation, and is essentially an unnatural habitat to which few species in the area are well adapted. Most of the birds that were common at nearly every other site – like the Common Bush-tanager, Silver-throated Tanager, and Brown-capped Vireo – were not seen here. The Rufous-collared Sparrow (right) and Yellow-faced Grassquit (seed-eating species) dominated the site. These species were also common at Site 4, but were absent from all of the more heavily forested sites. The Lesser Goldfinch (also a seed-eater) was the only species "endemic" to this site.

Site 4: In the lower meadow, near the intersection of the River and Plantation Trails. Vegetation is succesional, with a mixture of open, grassy spaces, shrubs, and young trees.

This site had mid-range values for diversity, abundance, and richness, and the second highest percentage of endemic species. To judge by its four most common species – Yellow-faced Grassquit (pictured) Rufus-collared Sparrow, Common Bush-tanager, and Silver-throated Tanager – Site 4 must be a hybrid of sites 2 and 3. In fact, it does have the young trees (including Cecropias) of Site 2 and the low shrubs and grasses of Site 3. The habitat seems to be especially favorable for the small, omnivorous tanagers. Seven species of tanager were observed here, more than at any other site. The Golden-hooded Tanager and Glue-gray Tanager were among its "endemic" species. Site 4 also hosted a relatively high diversity of flycatchers (four species), perhaps because the vegetation provided many exposed perches from which to catch insects in flight.

Site 5: Along the Rio Chirripo near Casa Amanzimtoti. Vegetation is the mature riparian forest of the north bank.

Since this site included the river, it hosted three aquatic species not seen at any other site. These were the Torrent Tyrannulet, the American Dipper, and the Louisiana Waterthrush. They all foraged for insects in the water, either from the riverbank or rocks in mid-stream. The most common bird was the Slate-throated Redstart. Site 5 also had a high diversity of hummingbirds (four species), which were attracted there by the many flowering plants. The Green Hermit was the most abundant of the hummingbirds, and was "endemic" to Site 5. Another beautiful species, seen only at this site, was the Blue-crowned Motmot (picture at right).

Site 6: Along the Uran Trail, between the Rio Uran suspension bridge and Rancho Don Victor, immediately after the entrance to Cloudbridge North. The vegetation is mature riparian forest (with a view into the canopy) and succesional thicket.

With 36 species observed, this site had the greatest diversity of birds. It is interesting to compare the results from Site 6 with those from Site 1. Both have high levels of diversity, but while Site 1 also has a high percentage of "endemic" species, Site 6 has the lowest level of endemism among all the sites. This is most likely due to its highly varied habitat. It has the mature trees of Site 1, the young trees of Site 2, and the open spaces and shrubbery of Site 4. It can support a wide variety of birds, but many of these birds also find their preferred habitat at other sites. The most abundant and often-seen species at Site 6 was the Emerald Toucanet, pictured at right, attracted there by a fruiting aguacatillo (wild avocado) tree. Many other species fed on this fruit, including the Squirrel Cuckoo, Collared Trogon, Black Guan, and, most notably, the Resplendant Quetzal (photo at top of page). A single male quetzal was regularly seen at Site 6. Several large, dead trees in the area may provide good cavity nesting sites for this species.

Detailed Quantitative Results. An Excel file, containing the avifauna species counts and charts measuring diversity, richness, abundance and local endemism, is available by clicking on the image at right. For more information write to Ian Giddy (see the contact page). Also see the descriptive Bird Sightings page.

Interested in doing research at Cloudbridge?
Reseachers must bring independent funding for their projects, including travel and living expenses. Send us some information about your research qualifications, what you wish to study, and when you can come. If your project is accepted, we'll assist in finding accommodation and provide access to the reserve. We'll also publish the results of the research on the Cloudbridge website. To discuss your ideas, contact Ian & Genevieve Giddy (see the contact page).