| Abstrakt: |
Simple Summary: This study describes how in 30 post-hatching days, captive barn owl chicks undergo postural changes, starting from a condensed egg posture in which their relatively big head is bent underneath the trunk, and culminating in the upright posture of adult owls. Interestingly, during the first 10 post-hatching days, while their eyes are still closed, their activity increases, following a mobility gradient that starts with lateral head movements that are followed by pivoting around the hindquarters, and then by shifting to forward progression. This gradient was previously described in the development of rat pups and in other mammals when they switch from immobility to activity. Once the eyes are opened, activity decreases and the chicks are mostly stationary, preoccupied with lateral and peering head movements, scanning the environment. The latter behavior is typical of adult owls when not on the wing. The chicks start flying on day 50, first by swooping down when placed on a perch and then actively flying in the aviary. Altogether, the development of movement in barn owls first demonstrates a conspicuous resemblance with a general mobility gradient and then speciation from that general developmental pattern to the typical barn owl behavior. Hatching captive barn owl chicks underwent four developmental phases. In the first 10 days (phase 1), behavior consisted of lateral movements that gradually changed to forward progression and peaked a few days before and after eye-opening. This behavior resembled a general developmental pattern that characterizes other vertebrates. Chicks also underwent a postural change, from head bent underneath the ventrum to resting on the rear end of the trunk with the head lifted in the air. Then, once their eyes were opened, chicks became more stationary and preoccupied with visual exploration, manifested in lateral head movements and peering episodes (phase 2, until day 20). The latter behavior, which is also typical of mature owls when not on the wing, characterized the chicks' behavior after post-hatching day 20 (phase 3), when their flight and contour feathers grew, along with shedding the down plumage and standing tall. Development culminated in active flight, first observed by days 50–60 (phase 4). Altogether, during post-hatching development, barn owl chicks gradually shifted from egg posture to the adult upright body posture. At the same time, their behavior consisted of speciation from the general developmental pattern to the typical stationary barn owl behavior, and, finally, flight was incorporated. [ABSTRACT FROM AUTHOR] |
