Volumen 14(3) Noviembre de 2010 - Eco-Index

Mesoamericana 14 (3) Noviembre de 2010we studied the use of live fences by migratory birds andspecies observed in local forest patches and agroforestryplots to determine whether management approach affectedthe presence and activity of these groups of species in livefences. We used species data and observations of in-fencebehaviors to explore contributions of live fences underdifferent management to their conservation value for birdspecies in the corridor area.Ma t e r i a l s a n d Me t h o d sWe conducted this live fence study on farmlands atthe Center for Tropical Agriculture Research andHigher Education (CATIE) in Turrialba, Costa Rica(approximately 2000 ha of agricultural area; lat 9°54’N, long 83°41’ W). The study site is located within theVolcánica Central-Talamanca Biological Corridor, whichencompasses 652,545 hectares in the provinces of Cartagoand Limón and includes the transition area betweenCosta Rica’s central mountain range and the TalamancaMountains (Desanti, 2008). The region is located 600 mabove sea level and experiences climate conditions typicalof the humid tropics, receiving 2636 mm of precipitationannually and average temp of 22 °C. We chose live fencesthat divide cattle pastures and are bordered by sugar cane,agroforestry plantings, remnant trees and forest patchesas this variety of landuses is representative of agriculturalareas throughout the corridor. Prior to current use forcattle production, pastureland at the site was in sugarcane production. The pasture that surround the selectedlive fences have been in use for the last 10-15 years andwere established by planting improved hybrid grass species(including Brachiaria decumbens, B. radicans) or were allowed toregenerate naturally. Live fences are dominated by plantedtree species including: Erythrina costarricense (poró), E. fusca,E. poeppigiana (poró gigante), Gliricidia sepium (maderonegro), Pithecellobium longifolium (sota caballo), Trichanteragigantea (nacedero), and Miconia sp. (canilla de mula).We recorded presence and resource use of bird speciesin 18 fences, through a single point count station locatednear the midpoint of each of the 18 fences studied. Weselected the fences according to three treatments designedto represent the range of management approachescommonly used by farmers in the region: 1) multistratalive fences (dominated by mature, un-pruned trees); 2)simple live fences (dominated by immature posts and treespruned every 6-12 months), and 3) a control treatmentcomprised of post-and-wire fences. We included sixreplicates representing both north-south and east-westaspects in each treatment. We categorized the fencesaccording to their average height and the radius of treesin the fences. Multistrata fences are composed of treeswith mean height >6 m and mean canopy radius >4 m.Simple fences were composed of trees with a mean height3 min height and they had a developed canopy structure. Weclassified the trees that did not meet these characteristicsas posts. All descriptive data are reported as raw means ± 1standard deviation unless otherwise indicated.We monitored bird species in fences at the study sitefrom February to July 2009. We used ten-minute pointcounts to record all species visiting the fences as well astheir behaviors (foraging, perching, or reproductive activity)while using the fences. We repeated the counts 10 timesin each fence for a total of 100 minutes of observation.We marked birds not actively using the live fences (e.g.flying over head or perched nearby) only as present.We did not include species that could not be identifiedin estimates of species richness or in the calculation ofthe diversity indices, therefore our reported values areconservative (Luck and Daily, 2003). We recorded behavioropportunistically during each observation period, and did53