Rodriguez el al. • VENEZUELAN BIRD SURVEYS 
235 
TABLE 2. Number of species observed using the data obtained through Survey 1. Survey 2, both surveys combined (SI 
+ S2) and the checklists, indicating the proportion (%) of all potential species in the 27 transects (1,033 spp.) and all known 
Venezuelan birds (1,383 spp.) that they represent. 
Method 
Observed 
% potential 
% Venezuela 
Survey 1 
526 
51 
38 
Survey 2 
465 
45 
34 
SI +S2 
593 
57 
43 
Checklists 
676 
65 
49 
150 and 90 min, respectively. SI + S2 pooled 
species detected on SI and S2 at each transect 
: 240 min of observation) and checklists contained 
additional opportunistically detected species. 
Thus, the highest species numbers corresponded 
lo the checklists, followed by SI + S2, SI. and S2, 
respectively (Table 2). 
The Chaol estimate of total richness based on 
SI data, considering number of individuals per 
species, was 608 ± 22 species, while the Chao2 
estimate using SI + S2 data, based on detections/ 
transect (n = 27), was 788 ± 36 species. A mean 
of 64.2 ± 6.3% of the species from S2 was 
detected in the first 3 min and our corrected 
estimate of species richness for S1 is 828.2 ± 95.5 
species. 
The SI + S2 species accumulation curve 
reached an asymptote value at 785 ± 11 species 
(K = 9.48 ± 0.35) (Fig. 2), while the asymptote 
based on Chao2 was 879 ± 11 species (K = 
3.47). These asymptotic values represent 76 and 
85% of all potential species, and 57 and 64% of 
all known Venezuelan birds, respectively. The 
extended extrapolated curve shows the number of 
new species detected in the survey would decrease 
dramatically beyond the sampled 27 transects, i.e.. 
</> 
a> 
o 
0 
CL 
co 
co 
o 
Number of transects 
FIG. 2. Accumulation curve from data of Survey 1 and 2 (SI + S2) (the area shaded around the line is the 95% 
confidence interval), and extended extrapolated curve (dotted) from the sampled 27 to 100 transects The asvmDtote of 
observed values is 785 species (K = 9.48), and that for the Chao2 estimator is 879 species (K = U7) 
