Understanding the multifaceted relationship between biodiversity and landus
e intensity is key to conservation policy. To begin to characterize this re
lationship in a tropical region, we investigated the bird fauna in an agric
ultural landscape in southern Costa Rica. Landsat Thematic Mapper (TM) data
show that about 27% of the land remains forested in the 15 km radius study
region encompassing our sites. The rest was cleared about 40 yr ago for re
latively small-scale coffee and cattle production, intermixed with other cr
ops. Our goals were to: (1) compare the composition of the avifauna found i
n forest-fragment and open habitats of the countryside; (2) assess the faun
al change that has occurred since deforestation: and (3) provide a baseline
for future comparisons.
We surveyed the avifauna of eight forest fragments (0.3-25 ha) and 13 open-
habitat sites (1.0 ha each) in the agricultural landscape. The pre-deforest
ation avifauna was approximated by the long-term bird list for the largest
forest fragment (Las Cruces, LC; 227 ha) in the study region. We assumed co
nservatively that a species recorded in LC but not detected elsewhere occur
red only in LC. Of the 272 locally extant bird species considered in this s
tudy, 149 (55%) occurred in forest habitats only. There was a significant p
ositive correlation between forest fragment size and species richness for t
hese forest birds. Of the remaining 123 species, 60 (22% of the total) occu
rred both in forest and open habitats. Sixty-three species (23%) occurred i
n open habitats only; the three nonnative species (1%) are in this group. B
ased on comparisons with larger forest tracts outside of the study region,
it appeared that between 4 and 28 species (1-9% of the possible original to
tals) have gone locally extinct since deforestation began. The avifauna of
open habitats was similar throughout the study region and did not vary with
proximity to extensive forest.
A substantial proportion of the native bird fauna occurs in a densely (huma
n) populated, agricultural landscape almost a half-century after extensive
clearance. There are, however, cautionary messages: (1) the common occurren
ce of forest birds in human-dominated countryside (including both forest-fr
agment and open habitats) does not necessarily imply that these species mai
ntain sustainable populations there; (2) about half of the species have lit
tle prospect of surviving outside of the forest; and (3) ongoing intensific
ation of land use may greatly reduce avian diversity in countryside habitat
s. Nonetheless, countryside habitats may buy time for the conservation of s
ome species; at best, they may even sustain a moderate fraction of the nati
ve biota.