Monteverde : Ecology and Conservation of a Tropical Cloud Forest

1983-1988- 1990 1991 1992 1993 1994 1995

1984 1989

Year

Figure 5.7. Year-to-year variation in the abundance of
anoiine lizards on the upper Pacific slope at Monteverde.
Numbers of lizards found per hour are based on sightings
in Zone 3 Oust west of the Preserve entrance). Sightings
were made along trails, mostly during mornings (0800-
1200) in May-October within a 30-ha area. Sampling
time per period was a minimum of 60 hr over at least 30
days. Cloud Forest Anoles (Norops tropidolepis) inhabit
the shaded forest understory, whereas Montane Anoles
(A/, altae) prefer open areas. Sampling effort was divided
equally between forest and overgrown pastures. Despite
extensive searches in 1996-97, neither species was
observed in the area.

est Racer, and Striped Litter Snake (M. Fogden, un-
publ. data). The pattern of change in abundance
included a decrease during 1986-92 and a partial re-
covery in 1993-94 (Fig. 5.8). For the pooled data, there
was a strong downward trend for 1986-92 (for snakes
found per hour, vs. year, Kendall's T = -1, P < .0006).
By 1991-92, the average search time per snake had
increased fivefold, to 43.8 hr. In 1993-94, it was 17.5
hr, or about twice what it had been in 1986-87. Al-
though most of the nine species showed this pattern
of decline followed by partial recovery, two seemed
to disappear from the area. The Green Frog-eater, the

1989 1990 1991

Year

Figure 5.8. Year-to-year variation in the abundance of

diurnal, frog-eating snakes in the PefSas Blancas valley

(Zone 6). Numbers of snakes found per hour are based on

pooled sightings of nine species in Zone 6 (see Sec. 5.4.1).

Sightings were made along trails, mostly during mornings

(0700-1200) in March-June within a 5-krn^2 area. Total

sampling time was 1520 hr (304 days; time per year for

1986-94 was, respectively, 195, 280, 440,105,150, 40,

135, 75, and 100 hr). Although sampling time in 1991

was comparatively small, results of the correlation

analyses (see Sec. 5.4.1) were the same when the data for

1991 and 1992 were combined.

fourth most common species in 1986-87, has been

absent since 1988. The Glossy Litter Snake, though

never common, was last seen in 1990. Observations

in March 1997 suggest that the partial recovery of

1993-94 has not been sustained. Forty-six hours of

search during favorable weather failed to yield a single

snake (M. P. L. Fogden, unpubl. data). On Monte-

verde's Pacific slope, many colubrid species, includ-

ing the Bronze-striped Parrot Snake (see Pounds and

Brenes, "The GTLC," p. 174), the Green Keelback (see

Sec. 5.1.1), and the Fire-bellied Snake (Fig. 5.9), like-

wise appear to have declined. Additional sampling is

needed to assess the status of snake populations.

5.4.2. Natural Sources of Mortality

Amphibians. Desiccation, parasitism, and predation

cause high mortality of anuran embryos and tadpoles.

The eggs of Fleischmann's Glass Frogs, laid on the

undersurfaces of leaves overhanging streams, are

vulnerable to desiccation, infestations of fungi and

drosophilid flies, and predation by daddy longlegs

(Phalangida) and crickets (Gryllidae; Hayes 1983,

1991). The eggs of leaf-breeding treefrogs (Agalychnis

and Phyllomedusa) often become prey for Cat-eyed

159 Amphibians and Reptiles