Although lowland tropical rainforests were once widely believed to be the archetype of stability, seasonal variation exists. In these environments, seasonality is defined by rainfall, leading to a predictable pattern of biotic and abiotic changes. Only the full annual cycle reveals niche breadth, yet most studies of tropical organisms ignore seasonality, thereby underestimating realized conditions. If human-modified habitats display more seasonal stress than intact habitats, then ignoring seasonality will have particularly important repercussions for conservation. We examined the seasonal dynamics of Amazonian mixed-species flocks—an important species interaction network—across three habitats with increasing human disturbance. We quantified seasonal space use, species richness and attendance, and four ecological network metrics for flocks in primary forest, small forest fragments, and regenerating secondary forest in central Amazonia. Our results indicate that, even in intact, lowland rainforest, mixed-species flocks exhibit seasonal differences. During the dry season, flocks included more species, generally ranged over larger areas, and displayed network structures that were less complex and less cohesive. We speculate that because most flocking species nest during the dry season—a time of reduced arthropod abundance—flocks are simultaneously constrained by these two competing pressures. Moreover, these seasonal differences were most pronounced in forest fragments and secondary forest, habitats that are less buffered from the changing seasons. Our results suggest that seasonality influences the conservation value of human-modified habitats, raising important questions about how rainforest organisms will cope with an increasingly unstable climate.

Species composition data were collected as described in this paper and Rutt et al. (2020): CLR followed flocks on foot and recorded species composition in 30-min time blocks. We curated the list of "flocking species" to exclude bycatch, which we considered to be any species other than the 105 that we listed in the appendices of these two papers (Appendix S1: Table S1 of this study and the Appendix of the Biological Conservation paper).

Rutt, C.L., Mokross, K., Kaller, M.D., and P.C. Stouffer. 2020. Experimental forest fragmentation alters Amazonian mixed-species flocks. Biological Conservation 242: 108415.

The 8 columns of the species composition data (Amazonian_flock_species_compositions_EcolAppl2020.csv) should all be fairly intuitive, except for species codes, for which we've deposited a separate key (Species_code_key.docx):

flock -- We have 12 flocks in this study, each with a unique name and a four-digit reserve code

date_cal -- This is simply the date

time -- CLR originally recorded species composition in 10-min timebands, which were later aggregated into 30-min timeblocks (timeblock)

vegetation -- We followed flocks in three treatments: primary forest (prim_forest), secondary forest (sec_forest), and ~10-ha fragments (10_ha)

network -- Each flock will contain two networks, one for the dry season and another for the wet season (flock_dry and flock_wet)