We report recent findings of Isthmohyla pictipes (Cope, 1875) in the Cordillera de Talamanca, Costa Rica, roughly two decades after it was last registered. We provide notes on microhabitat use, color variation, external morphology of adults and larvae, and geographic variation, and discuss some taxonomic characters employed to differentiate I. pictipes from I. tica (Starrett, 1966) and I. xanthosticta (Duellman, 1968). We also report fluorescence on the ventral surfaces of I. pictipes. Our findings are expected to shed light on the taxonomy of this species and should be useful in further population assessments and conservation plans.

We report the range expansion of the Gulf Coast Toad, Incilius valliceps (Wiegmann, 1833), from tropical moist forests to tropical wet forests and towards southeastern Costa Rica. We evaluated erroneous reports of this species in databases on the web. Also, we discussed that movements to areas with wet conditions for a species known from humid and xeric habitats can be explained by the trends in deforestation and increments of the dry conditions during recent decades in the country.

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.

According to Rensch’s rule, in species where males are the larger sex, increasing body size is coupled with increased sexual size dimorphism (SSD), whereas in species where females are larger, SSD decreases with body size. We describe the variation in SSD for body mass and its fit to Rensch´s rule in 45 species of Costa Rican hummingbirds. We examine SSD in body mass, bill length, and wing size and their fit to Rensch´s rule in nine species of hummingbirds for which we have detailed data. We expected that physiological constraints will limit the variation in SSD since hummingbirds have high metabolic rates, high dependence on energy-dense food, and high costs imposed by small size and hovering flight; these factors scale with body size and elevation. Large species should be physiologically capable of withstanding greater variation in SSD compared to small species, which are more energetically limited. Hummingbirds showed mixed allometry and fit Rensch's rule (slope of the RMA regression male vs female body mass = 0.8630). Eighty percent of the species showed male-biased allometry for SSD in body mass. Average variation in SSD was 12% and varied regardless of size. Physiological limitations act on hummingbirds as a group affecting SSD, independently of body size. SSD differences in body size, bill length, and wing area could influence ecological performance, sexual displays, food resource access, and foraging behavior. The SSD mixed allometry, and the positive relationship between the standard deviation of body mass, wing chord, and wing area with hummingbird size found only in males (9 species), suggests that selective pressures act differentially on the sexes and influence sexual niche segregation. Future research should examine intersexual variation in morphology, and quantify intersexual habitat use, niche segregation, and interspecific and intraspecific competitive interactions, targeting species located at the extremes of the Rensch's rule scatterplot.