San José, Costa Rica, since 1956

Monkey Populations Shrinking Fast

CORCOVADONATIONAL PARK, OsaPeninsula – A troop of squirrel monkeys swung playfully from tree branch to tree branch, dining on enormous chartreuse grasshoppers, or esperanzas, then flicking the leftovers to the ground like broken peanut shells.

Squealing amongst themselves, the titís, as they are known in Costa Rica, seemed to hardly notice the 15 or so basket-mouthed tourists standing on a park trail 50 feet below.

This kind of “up-close and personal” experience with wildlife in native, unaltered habitats, still typical of the southern PacificOsaPeninsula, is becoming increasingly rare elsewhere in Costa Rica as deforestation and disease take their toll on monkey populations, according to a comprehensive study conducted by a team of 18 national biologists over the past five years.

The study suggests populations of the country’s four species of monkeys have declined between 43% and 72% since 1995, and rampant deforestation and development are forcing those that remain into smaller and smaller areas.

Howler monkeys suffered the most in sheer numbers, dropping from an estimated 102,000 individuals in 1995 to 36,000 this year, according to University of Costa Rica biologist Ronald Sánchez.

In the same period, spider monkeys fell from 26,000 to 7,225 – a decline of about 72%. Squirrel monkeys and white-faced capuchins fared only slightly better – with populations decreasing by about 43% over the past 10 years, from 7,300 to 4,200, and 95,000 to around 54,000, respectively.

The numbers, cautions Sánchez, are estimates – extrapolated from studies in the country’s protected areas.

“It will never be possible to count every monkey. But no matter how we look at it, we see a drastic decline in populations. The reality is, the habitat is disappearing, and so are the monkeys,” he told The Tico Times this week.

Closer Inspection

The comprehensive study, conducted by biologists from the University of Costa Rica (UCR), the National University (UNA) and the University of Medical Sciences (UCIMED) looked at a sample of 325 monkeys, with a focus on their health and genetics.

Monkeys of all species were captured in study areas throughout the country using an elaborate system of nets and tranquilizer darts to avoid harming them, according to  Gustavo Gutiérrez, the UCR geneticist who coordinated the study.

“We knew getting these monkeys out of the trees would not be easy. Once we had them on the ground, we wanted studies of everything,” he explained.

Gutiérrez said contracting populations and habitat, if left unchecked, could lead to the extinction of all four species of monkeys.

“Deforestation has forced monkeys into smaller and smaller areas, which is seriously compromising their genetics,” he said.

The danger is one that even a layman can understand – push too many monkeys, too eager for sex, into too small a space – even the seemingly expansive OsaPeninsula – and inbreeding occurs, greatly reducing genetic vitality.

The result, Gutiérrez explained, is a weaker species – one less able to adapt to the effects of threats such as global warming, deforestation and encroaching human development and disease.

An example, Gutiérrez said, occurred in September and November 2005, when abnormally heavy rains and cold weather led to a shortage of food and a massive monkey die-off in CorcovadoNational Park – as much as 40% of the park’s total population was lost (TT,March 31, 2006).

Such a die-off, Gutiérrez said, is typical of a population in poor genetic health.

“Populations with little genetic variability are at a severe disadvantage when it comes to extreme events or catastrophes,” he said, citing weakened immune systems and higher susceptibility to disease and sickness.

Primate Ailments

Costa Rica’s monkeys are a sickly lot, according to Sánchez, who said they suffer from a laundry list of illnesses that seems to be growing.

Among the most common ailments observed in monkeys were eye problems, including cataracts, and skin pigment discoloration, Sánchez said, both problems likely caused by an excess of solar radiation.

Dental problems, which lead to difficulties chewing and eating, and sometimes death, were also common.

The cause of these medical issues has yet to be determined, but theories range from global warming to poor nutrition and compromised habitats. Toxins from agricultural chemicals used in banana, pineapple and citrus plantations are also likely to blame, Sánchez said.

Equally alarming, according to Sánchez, is the discovery of a malaria parasite in six of 104 howler monkeys tested for the mosquito-borne virus.

The strain of malaria, according to studies conducted by Misael Chinchilla, of the University of Medical Sciences, had never before been observed in Central American monkey populations.

The spread of such parasites among formerly healthy populations is just another example of the problems created when humans encroach on monkey habitat.

“As humans start to live closer and closer to the monkeys, the effects on their health could be serious,” Sánchez said.

These problems, Gutiérrez explained, are exacerbated when combined with the problem of the shrinking genetic pool – which leaves the species in a weakened state, and less able to resist such ailments.

“The preliminary data indicates there is very little genetic variability in monkeys –which puts them at serious risk of extinction,” Gutiérrez said.

Species at Risk

The spider monkey, a species that is highly dependent on intact primary forests – the same forests most threatened by logging and development – is of highest concern to Sánchez.

“Their future is in serious doubt – their numbers are falling fast,” Sánchez said.

Likewise for the diminutive mono tití, which now finds itself hanging by shaky limbs only in and around Corcovado and ManuelAntonioNational Park, on the central Pacific coast.

As Gutiérrez points out, even a single stroke of bad luck – a new disease, a freak weather incident, or further development or deforestation, and the titís and spider monkeys, crammed into increasingly small places with populations now critically reduced, could find themselves on the brink of extinction in Costa Rica.

The white-faced capuchin, which Sánchez says would join tourists “at the dinner table of their hotel,” if it could, is far more adaptable, and likely to fare better in the face of increasing development – though its numbers are dropping quickly too.

Complete results of the study – and recommendations – will be presented at a national symposium on the subject in July.

Sánchez said he hopes the information will help Costa Rica better manage the species and its ecosystems – for both abundance and their undeniable tourism appeal.

“We are a country that depends on our natural resources to attract tourism. If we lose that, I don’t know what we’ll have left,” he said.

Primates at Glance

Spider Monkey (mono colorado, mono araña)

Habitat: Found in rain and deciduous forests below 2,500 meters. Prefers primary forest.

Diet: Ripe fruit, leaves, flowers.

Estimated populations: 26,000 in 1995, 7,225 in 2007

Decline: 72%


Howler Monkey (mono congo)

Habitat: Found throughout country below

2,500 meters.

Diet: Fruit and leaves.

Estimated populations: 102,000 in 1995, 36,000 in 2007

Decline: 64%


Squirrel Monkey (mono tití)

Habitat: Found in the southern Pacific lowlands, concentrated around Corcovado and Manuel Antonio national parks.

Diet: Omnivore; eats insects, small fruits, leaves.

Estimated populations: 7,300 in 1995, 4,200 in 2007

Decline: 43%


White-faced Capuchin (mono cariblanco)

Habitat: Caribbean and dry deciduous forests on the Pacific slope. Very adaptable to human-altered habitats.

Diet: Omnivore; ripe fruit, insects, bird eggs, small squirrels, lizards.

Estimated populations: 95,000 in 1995, 54,000 in 2007

Decline: 43%


Source: Biologist Ronald Sánchez, University of Costa Rica (UCR)

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