"Abundance, Distribution, and Troop Composition of the Black Howler Monkey (Alouatta Pigra) in Different Forest Remnants in the Lachuá Ecoregion"

Abstract

This study analyzes the distribution, abundance, and troop composition of the black howler monkey, Alouatta pigra, in the Lachuá ecoregion. The forest remnants where the monkeys were located varied in size, vegetation cover type, and isolation distance between each individual. The effect of community representation of the black howler monkey on the abundance and distribution of these primates was also considered. In a total of 1,067 hours of searching, 414 individuals were observed, of which 403 (97%) formed 80 troops and 11 (3%) formed extra-troop groups, solitary individuals, and one adult female mantled howler monkey, A. palliata, that was part of an A. pigra troop. Habitat fragmentation was observed to modify the potential habitat for black howler monkeys by limiting the distribution of individuals to the few remaining forest remnants in their area of ​​influence and to the PNLL. These remnants are frequently isolated. Greater numbers of individuals and troops were detected in patches near hills, possibly related to a greater abundance of the ramon tree (Brosimum spp.) near archaeological sites in the area. In addition, an abundance of the food trees tamarind (Dialium guianense) and amate (Ficus spp.) was observed in this area. The average troop size in the patches (forested areas less than 4 km2) was 5.19 (±1.97 with a range of 1 to 2 individuals), in the hills (area of ​​18.09 km2) it was 5.35 (±1.70 with a range of 8 to 3) and in the PNLL (area of ​​31.74 km2) it was 3.89 (±1.33 with a range of 6 to 3). The average of the relative population density indices was 13.01 ind/km2 in the patches and 6.8 ind/km2 in the hills. The ecological relative density index in the PNLL was 1.8 and a range of 1.04 to 700.67 ind/km2 was observed. The composition of the total number of troops detected (N=80) was as follows: 34% adult males (N=136), 35% adult females (N=142), 6% juvenile males (N=24), 9% juvenile females (N=34), 1% unsexed juveniles (N=5), and 15% infants (N=62). The proportion of adult males was higher in areas with lower density (hills), and a high tendency towards polygamous and single-male troops was observed. The number of A. pigra individuals detected was higher in remnants with forest cover and in poorly isolated patches (81 to 262 m apart).