rarity of birds and its ecological context in the University of the Philippines
Vallejo Jr.* and Alexander B. Aloy
Institute of Environmental Science and Meteorology, College of Science
Villadolid Hall, University of the Philippines, Diliman, Quezon City
In this paper we use frequentist (classical) and Bayesian inference to estimate
the rarity of birds in the University of the Philippines Diliman campus. Rare
species have a detection probability of 1%. As sightings of certain species
of birds are extremely rare, a frequentist approach to estimation will often
result in overestimates of observation precision. Using McArdle’s rarity
and Bayesian inference we estimated the probability of detecting rare species
as between 4 to 10%. The Bayesian estimates are lower and may be a better method
for estimating rarity. The coefficient of variation (CV) of the frequentist
(24%) and Bayesian (25%) estimates are similar suggesting imprecision. Rare
species are likely to be detected in areas of campus with common and highly
abundant species. This may be an artifact of the fast paced Jokimäki method
that was used in surveys of bird abundances. The higher probability of detecting
rare species from the suggested 1% cutoff and similar CV estimates are likely
due to the small data set used in the estimations and the lack of prior information.
The ecological context of our observations is related to the increasing fragmentation
of habitat in the campus as a consequence of urbanization.
*To whom the correspondence should be addressed. E-mail:email@example.com
Received May 20, 2008; Accepted December 13, 2008.
Editor-in-charge: Porfirio M. Aliño