Evaluation of methodological protocols using point counts and mist nets: A case study in southeastern Brazil

Abstract

Despite their wide use in ornithological surveys, point counts and mist nets follow protocols developed in temperate regions, with little attention to possible modifications for tropical systems. Using these methods on a 3-month basis from December 2009-January 2011 in two forest fragments in southeastern Brazil, we wished to evaluate how long these locations needed to be surveyed with point counts for a relatively complete avifaunal inventory (at least 90% of all species and contacts), and if mist net hourly captures can equally detect numbers of species and individuals. Daily counting with four 20-min points during five consecutive days in a rain forest (MC) detected 90% of the estimated species richness after 20 h (60 20-min point counts), while 17 h (51 20-min point counts) did not detect 90% of the estimated species richness in a semideciduous forest (IT). The first 5 min of point counting in MC (63% of all species) and in IT (65%) detected significantly more species than the remaining minutes, but it took 15 min to accumulate 86% of all contacts in both forests. Consecutive 5-day mist netting (~ 9 h/day) resulted in 70.5 net-h/m2 (MC) and 74.8 net-h/m2 (IT) of sample effort, but 80-85% of the estimated number of species was obtained. Although accumulation curves showed no tendency towards stabilization of the number of observed species, the estimated number of species began to stabilize after the first 20 h in both forests. There was no significant difference in capture rates for both species richness and abundance among hourly net checks, but a trend in which these parameters were highest between the second and fourth checks of the day was observed. A 3-day (43.8 and 63.3 net-h/m2) mist netting section was enough to record 90% of the species captured during five days in MC and IT, respectively, while precise enough not to jeopardize species richness estimation. The number of individuals, however, decreased order 34% in MC and 38% in IT under the same conditions. Considering the number of net checks, 90% of the estimated species richness was captured until the 1100 h check in both remnants, while 67% of all individuals were captured until this same hour. Our results demonstrate that surveying the avifauna in these locations will require unique approaches, which must be tested before the beginning of point counting or net opening.