A comparison of the breeding biology of the Bornean Whistling-Thrush (Myophonus borneensis) and White-crowned Forktail (Enicurus leschenaulti borneensis)

Abstract

. Advances in understanding geographic patterns of life history variation depend on documentation of life history traits for species in poorly studied regions. In the tropics, most species have not had their life history traits described. We compared the reproductive biology of two closely related Muscicapids, the Bornean Whistling-Thrush ( Myophonus borneensis ) and the Bornean subspecies of the White-crowned Forktail ( Enicurus leschenaulti borneensis ), coexisting in Mount Kinabalu Park in Sabah, Malaysia. Both species specialize in riparian habitats, but whistling-thrushes are more adaptable to human presence and can be found nesting on and foraging around buildings, whereas forktails are more wary of humans. We located and monitored 77 forktail nests and 130 whistling-thrush nests from 2009 to 2020. Mean clutch size was 2.00 ± 0.04 for forktails and 1.89 ± 0.04 for whistling-thrushes. Mean egg mass at lay was 4.07 ± 0.04 g for forktails and 11.65 ± 0.12 g for whistling-thrushes. Forktail incubation period (17.0 ± 0.42 d) was slightly shorter than for whistling-thrush (18.6 ± 0.19 d), but both species had similar rates of incubation attentiveness