As tropical forests are frequently impacted by human disturbance, forests in various stages of disturbance recovery are increasingly important for maintaining biodiversity. However, the mechanisms through which disturbance affects wildlife remain poorly understood. Here, we used mist net capture data to compare bird communities in three tropical forest habitats representing various disturbance intensities: undisturbed primary forest, selectively logged forest (low disturbance), and secondary forest regenerating on abandoned agricultural fields (high disturbance). We found that after a 19-year recovery period, low disturbance sites contained similar bird communities to undisturbed sites. Regenerating agricultural fields, however, had lower species richness and distinct bird communities, with fewer insectivores and more nectarivores than other sites. Structural equation models revealed that the impacts of disturbance intensity on bird communities were partially explained by changes in vegetation structure: ant-following insectivore abundance declined with disturbance intensity as ground cover vegetation increased, and nectarivore abundance increased with disturbance intensity as tree density decreased. Our results suggest that selectively logged forests can regain pre-disturbance bird diversity and vegetation structure within two decades, provided that they are protected from further disturbance and located near source species pools. Increasing tree density and decreasing ground-level vegetation in secondary forests may improve these areas as habitat for forest-interior birds.

Bird Sampling

      Fieldwork for this study took place at Allpahuayo-Mishana National Reserve (RNAM) in Loreto, Peru, from March 11 to May 24, 2023. This timeframe corresponds with the local rainy season, which is the breeding period for most tropical birds in the area. At each site, we established a network of 10 mist nets (2.6 x 12 m, 36 mm mesh size) to sample the understory bird community. Nets were generally set up in an L formation, with two straight lines of five nets established at a 90° angle, though the exact formation depended on the presence and avoidance of natural obstacles such as slopes, streams, and large trees at each site. The size of each net array was approximately 70 x 70 m. Mist nets were opened at dawn and operated for approximately 8 hours each day, except during periods of inclement weather such as rain or strong wind, and were checked for birds every 15-20 minutes. No speakers or callback devices were used to attract birds to nets. All captured birds were identified to species using the field guide Birds of Peru [39], and then released at the location of their capture. To distinguish new captures from recaptures, we snipped approximately 1 cm from the farthest right tail feather of each newly captured bird. We did not band birds because the vast majority of the region’s birds are nonmigratory, and all sampling at a given site occurred within 2-3 consecutive days. We operated nets for 2-3 consecutive days at each site until completing 160 net hours (where 1 net hour is the equivalent of 1 mist net being open for 1 hour). Sites of different forest types were sampled on a rotating basis, in an effort to reduce temporal pseudoreplication by minimizing successive sampling of sites with the same disturbance history. However, back-to-back sampling of sites with the same disturbance history did occasionally occur due to logistic constraints. To verify that sampling date was independent of disturbance history in our dataset, we used an ANOVA to test for a significant relationship (p < 0.1) between the sampling date and disturbance history. All mist netting and fieldwork activities were approved by the Servicio Nacional de Áreas Naturales Protegidas por el Estado (SERNANP) of Peru, and carried out under SERNANP Permit # 003-2023-SERNANP-JEF.

Vegetation Sampling

      We characterized the vegetation structure of each site by quantifying the following seven vegetation variables: tree density, average tree diameter, liana density, average liana diameter, canopy cover, understory vegetation density, and ground cover vegetation density. To this end, we performed vegetation surveys in three 10 x 10 m plots at each site. Each plot contained five discreet sampling points: one in each of the four corners, and one in the middle of the plot. We established the first plot one m to the right (from the perspective of a researcher facing down the net formation) of the beginning of the first net lane, the second plot one m to the left of the beginning of the sixth net lane, and the third plot one m to the right of the end of the tenth net lane. Within each 10 x 10 m plot, we counted and measured dbh (cm) of each tree > 10 cm, and each liana > 2.5 cm. At each of the five sampling points within a plot, we estimated the percent cover of understory vegetation (within 0.5 and 3 m height), ground cover vegetation (> 0.5 m), and bare ground, within a 1 x 1 m frame. At the center sampling point of each plot, we estimated percent canopy cover using a spherical densiometer (Forestry Suppliers, convex model A). Measurements of each variable were averaged within a site to estimate site-scale vegetation structure.