Abstract:
Standardized methods for biodiversity monitoring are needed to
evaluate conservation efforts. Acoustic indices are used in biodiversity
assessments, but need to be compared to traditional
wildlife methods. This work was conducted in the Santa Rosa
National Park between June and November, 2015. We installed
recorders and conducted bird point counts in twelve sampling
sites. We compared acoustic indices (Acoustic Evenness Index
[AEI], Acoustic Diversity Index [ADI], Acoustic Complexity Index
[ACI], Bioacoustic Index [BIO], Normalized Difference Soundscape
Index [NDSI], Total Entropy [TE], Median Amplitude
Envelope [MAE], Number of peaks [NP]) with indices from bird
point counts (Bird Abundance, Bird Richness, Bird Diversity and
Bird Evenness), and discuss the utility of acoustic indices as
indicators for biodiversity monitoring in tropical forests. ADI, ACI,
BIO and TE presented a similar temporal pattern peaking
between 5 am and 6 am; and an additional peak at 5 pm, except
for ACI. These patterns were consistent with the daily biological
rhythms. AEI, ACI, BIO and Bird Abundance were related to
characteristics of younger forests (lower percentage of canopy
cover) but NP, ADI, TE, Bird Diversity and Bird Evenness were
related to characteristics of older forests (higher percentage of
canopy cover and a lower number of patches). ACI was positively
correlated to Bird Abundance and NP was positively
correlated to Bird Diversity. ACI reflects biological activity, but
not necessarily a more diverse bird community in this study area.
This might be an indication of a strong acoustic competition, or
several highly dominant bird species in younger forests. Furthermore,
acoustic communities in tropical forests commonly
include insects (cicadas) and frogs, which might affect resulting
acoustic indices. A variety of methods are probably needed to
thoroughly assess biodiversity. However, a combination of
indices such as ACI and NP might be considered to monitor
trends in abundance and diversity of birds in dry forests.
