Biology of alpine accentor (Prunella collaris) VIII. Growth and postnatal development
62 measurements of 91 nestlings and juveniles of Prunella collaris were taken in the High and Low Tatras (Western Carpathians). Growth curves of head, bill, hind limbs, forelimbs, primaries, rectrices, as well as total wing and body weight were described. The strong isometry between the tarsometatarsal and antebrachial skeletons and the rapid growth of the wing bones in the first half of nestling development should be correlated with the intensity of activities involving the fore and hind limbs. The hind limbs of birds are not only responsible for supporting the body and moving about on the ground, but also play a key role in flight during take-off and landing. The bones of the legs are subjected to axial, bending, and torsional loads. Accentors do not show a typical sigmoidal curve in weight gain like some other altricial species. Particularly in the first few days after hatching, weight gain is high, indicating a short-term presence of chicks in the nest. Hatchlings grow at about the same rate during the first half of the nestling period, and later, hatched nestlings grow at about the same rate as their older siblings, only lagging in development at the time of hatching. During the second half of the nestling period, the rate of feather growth relative to weight is higher in younger chicks than in older chicks. In older chicks, feather growth slows as the weight of the internal organs increases, so that by the time the nestlings leave the nest, younger and older siblings are already at approximately the same developmental level. This is achieved over a period of two or three days as the chicks move around under rocks.
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