Recent publication on dendrobatids: "Diel activity patterns of the sympatric poison dart frogs Dendrobates auratus and D. pumilio in Costa Rica" by Brent M. Graves (Journal of Herpetology, Vol. 33, No. 3, pp.375-381. 1999)

In this paper the author describes the activity patterns of D. auratus and D. pumilio in a 0.1-hectare patch of late-successional, secondary forest at La Suerte Biological Station. By studying the two species in sympatry (i.e. living together), the author knew that differences in behaviour were not due to variations in weather, daylength, etc., as may be the case when widely-separated populations are compared. 
The author walked along three, fixed routes at 45-minute intervals between dawn (05.30h) and dusk (17.30h) on nine days, recording the number of frogs of each species and whether each frog was on the ground or on an 'elevated perch'. The number of frogs counted during each walk was used as a measure of frog activity. The activity of D. pumilio increased rapidly after dawn, peaked between about 08.00h and 09.30h, then declined throughout the rest of the day. 
The activity of D. auratus was clearly different, being more evenly spread throughout the day, but with two apparent peaks - at late morning and early afternoon. The author makes a brief comparison between his results and those of some other studies of the same species, one of which (Jaeger & Hailman, 1981; Biotropica, 13: 59-65) apparently found that D. auratus were most active in early morning and late evening, and inactive at midday. 
Given those results, one wonders whether both species were keeping out of the way of the midday sunshine - I would.
Dr. Clive Cummins