Costa Rica Eco Report,
April 2009
by Alberto Herrera,
Eco Director

The Forest of the Osa Peninsula

- A Wealth of Species -

All Tropical Rain Forests are rich in species – much, much richer than the broadleaf and coniferous forests of temperate regions.But the forests of different tropical regions are not all the same.

The Asian Island of Borneo and the Western part of the Amazon share the reputation of having the most diverse or species – rich forest in the world.For years it has been known that in these areas one may find more than 200 different woody species in a single hectare of forest.In recent years, numbers of 300 and even more have been encountered in one – hectare plots in Amazonian Peru and Ecuador.

Although the forest of the Osa does not reach these impressive numbers of species, it turns out that it is still among the richest of forests in Latin America. Only some forests in The Western Amazon and Pacific Colombia contain more species – than the Osa, whereas all of Mexico and Central America north of the Osa, Northern South America, East Amazon and Coastal Brazil contain less.

How do you measure the richness of woody species?
To measure and compare figures on numbers of species may be a very daunting task. For example, the National Institute of Biodiversity in Costa Rica, INBio, on their internet-homepage (www.inbio.ac.cr/es/biod/Biod.html) illustrates the biological richness of the country by the number of tree species in Costa Rica with those of Colombia and Brazil, correcting for the great differences in national territory. INBio finds that for every 6-tree species in Brazil there are 35 in Colombia and 295 in Costa Rica!

This comparison, however, is completely misleading. You must compare only what is truly comparable, and in this case, you can only compare the forest diversity in Costa Rica, Colombia and Brazil by taking similar sizes of samples from the various countries, for example choosing Brazilian and Colombian provinces of the same sizes as Costa Rica.

The most common way of describing the species richness, or diversity, of tropical rain forests is to count all the species that you find among all the living stems of 10 cm diameter or more in one hectare of forest. This measure has to this day scored up to 307 species, a figure encountered in Cuyabeno, Ecuador.

In Costa Rica the highest count is 178 species, in one hectare in the Aguabuena area, of the Osa Peninsula. This sounds as if the Osa Forest is much less diverse than the Amazonian forests. But this is not so. It turns out that only a limited part of the Amazon is actually richer.

Comparing one-hectare plots has among scientists for decades been an accepted way of evaluating the differences in species richness between different rain forest areas.

But one must NOT rely on this alone.

The reasons are the following:

1) Stem density varies between regions, and the numbers of species are naturally a function of number of stems, NOT of the area as such. If you happen to expand the area of your sample plot without including additional trees, the number of species will obviously remain unchanged. In contrast, if you within your sample discover additional trees belonging to species not registered in the plot before, these will add to the number of species without changing the area of the plot.

2) The shape of the plot influences the diversity of the plot. The more compact the shape, the more uniform is the forest. The longer the plots is, the more variation is included. Many one-hectare plots are shaped as transects 10 meters wide and 1000 meters long.

Recently, a study revealed that this shape includes 10% more species than a plot shaped like a square of 100 by 100 meters. Likewise, a plot of 20 by 500 meters includes 5 % more species than the square.

3) These life forms included in the study also influence the number of species. Today, most studies include all stems, but until some 20 years ago it was common to include only free – standing trees and palms, and not lianas and climbers. Early studies did not even include palms.

References:

The Forest Of the Osa Peninsula. Thomsen, Karsten

The Flowering Plants of the Golfo Dulce. Weber, Anton (Editor)

Costa Rica Eco Report,
March 2009
by Alberto Herrera,
Eco Director

Observing Mammals in Costa Rica's Tropical Rain Forest

Compared to animals such as birds, or insects, mammals are hard to observe in the field for several reasons. First, larger mammals, especially carnivores, tend to be less numerous than smaller animals because they are situated higher up the food pyramid. For example, a jaguar needs to eat many medium-sized animals, and each of those medium-sized animals needs to eat smaller animals or other organisms, and so on down the food chain, such that the jaguar is necessarily much more rare than smaller animals.

Secondly, while we are predominantly diurnal and ground dwelling, most mammals are neither. Of Costa Rica’s roughly 225 terrestrial and freshwater species, less than 30 are consistently active during the daytime. Even if one excludes the country’s 116 or so Bat species, about three quarters of the remaining species are active mostly at night. Likewise, more than three quarters of Costa Rica’s mammals either fly or spend a significant portion of their time up trees, under the ground, or in water.

Finally, most mammals tend to be shy. They can use their keen senses to detect people, along with their generally cryptic coloration and superior speed and agility to evade them.

Given all this, it is helpful to bear in mind a few simple tips that will increase the chances of finding mammals. One necessity is to walk quietly and listen. Although mammals tend not to be as vociferous as many other animals, a few do make conspicuous and frequent vocalizations.

Mammals such as Monkeys, Kinkajous, Coatis, or Squirrels are often located thanks entirely to their calls. Even mammals that call rarely can still be heard as they move through the vegetation. Canopy dwellers in particular are apt to shake branches as they move around: they may also draw attention by dropping pieces of food to the ground.

Another helpful strategy is to locate feeding sites and wait quietly nearby or check the sites frequently. A large Fig Tree or other fruiting species can attract a variety of mammal species in the course of a day or night. Of course, one can learn a lot about mammals in the field without ever seeing them. Signs such as scat ( fecal droppings), tracks, dens, runways, or indications of feedings areas can reveal the presence of elusive species and may provide clues about these mammals’ natural history as well.

The most frequently observed mammal sign is tracks, and Costa Rica’s muddy trails, sandy beaches, and riverbeds are excellent track substrates.

References:

Costa Rican Natural Histiry; Janzen, Daniel; editor.
The Natural History of Costa Rican Mammals; Wainwright, Mark

Check out our In-Depth Costa Rica Tours & Spa Site at
www.costaricaecotour.com

Costa Rica Eco Report,
February 2009
by Alberto Herrera,
Eco Director

Migratory Birds in Costa Rica and Central America
Each year, billions of birds spend the summer raising families in North America, then funnel into the small land mass found in the Caribbean and Latin America. Central America not only provides homes for many migratory birds for six to nine months a year, but is quite literally a bridge which connects the tropical forests of South America with the temperate zone woodlands of North America.

Tody Flycatcher

A Continual Tide of Birds
The number of birds moving across the Central America land bridge is staggering. Based on crude calculation it is reasonable to guess that as many as two to five billion birds leave North America each autumn.

Many settle in México and the West Indies, and a smaller portion fly straight to South America without stopping. The rest of the migrants, perhaps one-third of the total number, either spend the winter in, or migrate along the isthmus.

Diversity of Birds
Not just sheer numbers, but also the diversity of migratory birds is impressive.

Over 120 species of migratory birds, or about one of every 10 Central America species, regularly visit the region from North America. These species belong to a large number of families representing very different ways of life.

Among the ranks of the migrants we find one specie of Hummingbird, feeding almost exclusively on flower nectar; nine species of Birds of Prey; five species of Swallows, hawking for small flies and mosquitoes; a dozen Tyrant Flycatchers; four Thrushes; six Vireos and 24 species of small insect-eating Wood Warblers.

In addition to these migrant land birds, the Bay of Panama hosts one of the largest concentrations of migratory shorebirds in the New World Tropics.

The Migrant Map
The abundance of migratory birds in Central America is not hard to understand. Close to North American breeding areas, this narrow ribbon of tropical land is the only possible overland route between North and South America. Many species of migrants prefer one coast over another or forest in a particular elevation band. As the isthmus narrows in Panama, these migratory corridors thin to the point of vanishing.

Chestnut-sided Warbler

Closely related species often divide up the tropical map. So, in addition to the overall abundance of birds, Central America hosts most of the world’s populations of a number of migrant species including the Chestnut-sided Warbler (Dendroica pensylvanica), Golden-winged Warbler (Vermivora chrysoptera), Scissor-tailed Flycatcher (Tyrannus forficatus) and Philadelphia Vireo (Vireo philadelphicus).

References: Bridging the Americas: Migratory Birds in Costa Rica and Panama

Costa Rica Birding: Basic Recommendations for the Observation of Birds in the Field.

Birds in Costa Rica are found in a wide variety of different places, which vary from natural conditions to altered environments. They are commonly located in forest areas, second growth zones, mangroves, lagoons and rivers, including gardens, buildings, churches and parks in urban areas. Observing and studying birds is an interesting activity, providing knowledge and wonderful surprises.

The observer must have good visual and auditory capacities, patience, discipline and perseverance in order to obtain the essential information on a determined species. One must frequently remain quiet, silent, and attentive during long hours, generally under unfavorable field conditions. Nevertheless, in most cases, these difficulties are amply rewarded with the personal satisfaction of accomplishing the planned objectives and having the unique experience of admiring rare and beautiful birds in their natural habitat.

During Costa Rica Bird watching Tours, it is advisable to move in small groups, walking slowly and carefully, in the most cautious and silent manner. Unnecessary conversation with other companions must be avoided so that the birds will not be disturbed or scared away. In addition, it is convenient for participants to wear the correct clothing to avoid sharp contrast with the surroundings environment, thus disrupting the birds. In order to be successful in identifying birds in the field, it is highly advisable to locate them in their natural habitat at the correct time, according to the behavior pattern and ecological requirements of each species.

In general, most diurnal birds and those associated with forested areas are usually found active from sunrise until 8 or 9 am, and later after 2 or 3 pm. However, there are exceptions, such as aquatic species, which remain active throughout most of the day. In general, knowledge of periods of activity of the different bird species, their preferred habitats and other important aspects related to their behavior facilitates observation.

The minimum equipment necessary to observe and identify birds in the field consists of a pair of standard binoculars, a small notebook, field guides and possibly a telescope, camera or video recorder as optional accessories.If you would like to learn more about these birding tactics, or put some of your own ideas into practice in the jungle, come visit us at Crocodile Bay and show us what you have got!

References

1. Birds of the Rain Forest Costa Rica. Hidalgo, Carmen

2. . A Guide to the Birds of Costa Rica, Stiles and Skutch

Costa Rica Eco Report,
December 2008
by Alberto Herrera,
Eco Director