Table 1 Cuckoo nestling development characteristics, recorded at 3-day intervals

1–3

Hatched with pinkish skin, yellow extremities, and grey eyelids. No neossoptiles (natal down feather) present. No pins were visible. A prominent cavity on the lower back aided eviction efforts. The gape color was diffuse red/orange without any conspicuous markings. The bill was pale yellow and the rictal flanges were a more saturated yellow color. This appearance lasted to day 3, when alar pins started emerging in the subcutaneous layer and skin darkened (n = 12)

4–6

Skin darkened, appearing more red/purple/brown, with darker coloration over emerging teleoptiles. Remiges emerged and pierced the skin on the alar tract. Rectrices on the caudal tract emerged and pierced the skin. The contour feathers emerged and pierced the skin on the capital and ventral tracts. Pin feathers on the femoral and crural tracts appeared. Eyes started opening (earliest on day 5). The base of the bill darkened, whereas the bill tip remained pale yellow and the rectal flanges brighter yellow. The gape turned deeper reddish (n = 12)

7–9

Pin feathers on the lower part of the dorsal tract emerged and together with the crural and femoral tract pierced the skin. All teleoptiles showed rapid growth. The alar remiges pins turned paler at the outer end and started erupting. Eyes continued opening. The gape turned deep red (n = 7)

10–12

Ventral, femoral, capital, and caudal tracts erupted. Alar tract continued unsheathing. Eyes were open (n = 6)

13–15

Dorsal tract started erupting. Extensive unsheathing occurred on all teleoptiles. Exposed feathers covered a large number of hidden pin sheaths (n = 6)

16–18

The plumage appeared buffy and completed, mostly true for contour feathers. However, primaries and secondaries, as well as rectrices, were unsheathed slightly more than halfway. Pin sheaths on dorsal tract were still visible (n = 5)