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Abstract The conversion of natural habitats to human land uses often increases local temperatures, creating novel thermal environments for species. The variable responses of ectotherms to habitat conversion, where some species decline while others persist, can partly be explained by variation among species in their thermal niches. However, few studies have examined thermal niche variation within species and across forest‐land use ecotones, information that could provide clues about the capacity of species to adapt to changing temperatures. Here, we quantify individual‐level variation in thermal traits of the tropical poison frog,Oophaga pumilio, in thermally contrasting habitats. Specifically, we examined local environmental temperatures, field body temperatures (T_b), preferred body temperatures (T_pref), critical thermal maxima (CT_max), and thermal safety margins (TSM) of individuals from warm, converted habitats and cool forests. We found that frogs from converted habitats exhibited greater meanT_bandT_prefthan those from forests. In contrast,CT_maxandTSMdid not differ significantly between habitats. However,CT_maxdid increase moderately with increasingT_b, suggesting that changes inCT_maxmay be driven by microscale temperature exposure within habitats rather than by mean habitat conditions. AlthoughO. pumilioexhibited moderate divergence inT_pref,CT_maxappears to be less labile between habitats, possibly due to the ability of frogs in converted habitats to maintain theirT_bbelow air temperatures that reach or exceedCT_max. Selective pressures on thermal tolerances may increase, however, with the loss of buffering microhabitats and increased frequency of extreme temperatures expected under future habitat degradation and climate warming. Abstract in Spanish is available with online material.