Timing Is Everything: Acoustic Niche Partitioning in Two Tropical Wet Forest Bird Communities

When acoustic signals sent from individuals overlap in frequency and time, acoustic interference and signal masking may occur. Under the acoustic niche hypothesis (ANH), signaling behavior has evolved to partition acoustic space and minimize overlap with other calling individuals through selection on signal structure and/or the sender’s ability to adjust the timing of signals. Alternately, under the acoustic clustering hypothesis, there is potential benefit to convergence and synchronization of the structural or temporal characteristics of signals in the avian community, and organisms produce signals that overlap more than would be expected by chance. Interactive communication networks may also occur, where species living together are more likely to have songs with convergent spectral and or temporal characteristics. In this study, we examine the fine-scale use of acoustic space in montane tropical wet forest bird communities in Costa Rica and Hawai‘i. At multiple recording stations in each community, we identified the species associated with each recorded signal, measured observed signal overlap, and used null models to generate random distributions of expected signal overlap. We then compared observed vs. expected signal overlap to test predictions of the acoustic niche and acoustic clustering hypotheses. We found a high degree of overlap in the signal characteristics (frequency range) of species in both Costa Rica and Hawai‘i, however, as predicted under ANH, species significantly reduced observed overlap relative to the random distribution through temporal partitioning. There was little support for acoustic clustering or the prediction of the network hypothesis that species segregate across the landscape based on the frequency range of their vocalizations. These findings constitute strong support that there is competition for acoustic space in these signaling communities, and this has resulted primarily in temporal partitioning of the soundscape.

Vapor plumes in a tropical wet forest: spotting the invisible evaporation

Forest evaporation exports a vast amount of water vapor from land ecosystems into the atmosphere. Meanwhile, evaporation during rain events is neglected or considered of minor importance in dense ecosystems. Air convection moves the water vapor upwards leading to the formation of large invisible vapor plumes, while the identification of visible vapor plumes has not yet been studied. This work describes the formation process of vapor plumes in a tropical wet forest as evidence of evaporation processes happening during rain events. In the dry season of 2018 at La Selva Biological Station (LSBS) in Costa Rica it was possible to spot visible vapor plumes within the forest canopy. The combination of time-lapse videos at the canopy top with conventional meteorological measurements along the canopy profile allowed us to identify the driver conditions required for this process to happen. This phenomenon happened only during rain events. Visible vapor plumes during the daytime occurred when the following three conditions are accomplished: presence of precipitation (P), air convection, and a lifting condensation level value smaller than 100 m at 43 m height (zlcl.43).

Amphibians and Reptiles of the Tirimbina Biological Reserve: a baseline for conservation, research and environmental education in a lowland tropical wet forest in Costa Rica

The Tirimbina Biological Reserve is located in the lowlands on the Atlantic versant of Costa Rica. We provide an updated comprehensive herpetofauna species list and summarize the results of all the herpetofauna research conducted at Tirimbina over the last 10 years (2009–2019) across a variety of microhabitats. We also added historical records from occasional sightings and reports from researchers, staff, visitors, interns, fellows, and volunteers since the 1990s. We found 52 amphibian and 78 reptile species on the reserve, including a few species considered at-risk according to the IUCN Red List. We conclude that Tirimbina is a herpetofauna biodiversity hot spot in Costa Rica because it provides unique habitat characteristics for a variety of species, including habitat for both forest and forest-edge specialists.

Acoustic niche partitioning in two tropical wet forest bird communities

When acoustic signals sent from individuals overlap in frequency and time, acoustic interference and signal masking may occur. Under the acoustic niche hypothesis (ANH), signaling behavior has evolved to minimize overlap with other calling individuals through selection on signal structure and the sender’s ability to adjust the timing of signals. In this study, we examine the fine-scale use of acoustic space and the relevance of the acoustic niche hypothesis in two montane tropical wet forest bird communities (Costa Rica and Hawai’i) that vary in bird species richness. We used a null model approach to test the prediction that there are differences between observed and expected signal overlap in both communities. As predicted under ANH, we found much lower overlap of acoustic signals than expected by chance. In addition, spectral and temporal overlap between different signals was far more common in Hawaii than Costa Rica. These findings constitute strong support that there is competition for acoustic space in signaling communities, and this has resulted in temporal and spectral partitioning of the soundscape.

Extension of the known geographic distribution of Greenhall’s Dog-faced Bat, Cynomops greenhalli Goodwin, 1958 (Chiroptera, Molossidae): first records in Costa Rica

Specimens of the Neotropical dog-faced bats of the genus Cynomops Thomas, 1920 are poorly represented in museum collections, and the geographical distributions of the eight species are not well known. We report voucher specimens that confirm the presence of C. greenhalli Goodwin, 1958 in the Tropical Wet Forest of Costa Rica. These specimens represent an extension of the distribution into the Caribbean Central America.

First record of Synagelides Strand, 1906 (Araneae: Salticidae) from Sri Lanka: description of four endemic species from tropical wet forest of the island

Synagelides Strand, 1906 is recorded for the first time in Sri Lanka. Four new species are described and illustrated: S. hortonensis sp. nov., S. lakmalii sp. nov., S. rosalindae sp. nov. and S. orlandoi sp. nov. A key to the four new species is given.