Ontogeny of heart rate in embryonic and nestling crows (Corvus corone and Corvus macrorhynchos)

The developmental patterns of mean heart rate (MHR) and instantaneous heart rate (IHR) were investigated in embryos and chicks of altricial Corvus col one and Corvus macrorhynchos. The MHR of embryos increased linearly with t ime from 250 beats.min(-1) at mid-incubation to 290 beats.min(-1) in hatchl ings. MHR during the pipping period was maximal, but only marginally higher than in hatchlings. MHR was stable at about 290-300 beats.min(-1) during t he 1st week after hatching. Spontaneous heart rate (HR) decelerations and a ccelerations were found in embryos and chicks, disturbing the baseline HR w ith increasing frequency during development. However, the IHR accelerations developed later and were less frequent than in precocial species. IHR and body temperature decreased during mild cold exposure (23-25 degrees C) and IHR accelerations were reduced in nestlings during the 1st week. We suggest that the development of parasympathetic control of HR in crows occurs at 6 0% of incubation, similar to precocial embryos, but sympathetic control may be delayed and suppressed in contrast to precocial embryos.