Growth of the young

At hatching, the young flycatchers arc very helpless, with large heads, shapeless bodies, poorly developed legs and wings, and closed eyes. Their bodies are reddish and entirely naked and there are only a few tufts of down on the head. The only sound they can manage is a feeble chirping. Withoutthe warmth of the nest they would quickly die, and for the first few days all they can do is raise their heads, open their beaks, and chirp hungrily. In the darkness of the nest box's interior, the parents arc guided by the yellow edging on the young birds' beaks, and the reddish yellow spots inside the mouths of the young trigger off the parents' feeding instinct. The young also normally swing their heads back and forth, and if any of them are in a poor condition and cannot manage this action, they will receive no food and will die rapidly.

Forthe first eight days, the young birds arecomplctely blind and lieat the bottom of the nest. After ten days they can stand on their legs and thus raise their bodies. The wings, legs, and eventually the coat of feathers develop. The sheaths of the developing feathers grow up out of the skin on the head and wings after five days, and after nine days the feathers themselves grow out and slowly lengthen. However, even when the plumage is almost fully formed, some of the original down can still be seen. After eighteen days the young birds are a grey-brown colour, but they do not acquire the colouration of the adult bird until they are in their winter quarters.

The female's weight is normal during egg laying and incubation, but with hatching and feeding the young it falls rapidly. She will lose around 3 ┬╗rams up until the time when the young leave the nest. The male also loses weight, though only about 1 gram.

The young in the nest do nothing but eat and sleep. They arc quiet while their parents are away, but upon their return they chirp and gape vigorously. The young themselves cannot take the food which their parents have brought and must have it stuffed down into their gaping mouths. It is a busy time for the parents. Once the young arc several days old feeding starts at dawn, which in Sweden will be around 2am and continues until 9.30pm. In a nest which 1 studied, there were five young which had 590 meal times each day, which means that each bird received about 118 meals per day. The male averaged three insects at each feed and the female 1.5. On this basis the male, which fed the young 240 times each day, on average provided about 720 insects per day, while the female, provided about 525 insects in her 350 feeding sessions. This gave a total of 1245 insects per day, and as the young stayed in the nest for 19 days, they consumed altogether about 23,655 insects. In one year, there were 33 breeding pairs, so a grand total of 781,000 insects, midges, flies, etc, must have been used to feed the young during their time in the nest box alone.

When a young bird is fed by its parents it lifts up its rear end moments later and excretes its waste. The waste is enclosed in a soft membrane (the faecal sac) which does not break, making it possible for the parents to remove the excreta without soiling the nest bowl. Both parents remove waste, the male 65 times per day and the female 35. These sacs are carried at least 10 metres from the nest.

As the young get older the waste has to be removed more frequently, so that with 7-dav-old young waste is removed after every 10 15 meals, and with young which arc almost ready to fly it is removed after every 6 7 meals.

This particular task is important for both hole-nesting birds and those which build nests in the open. For hole nesters it is a matter of hygiene, but for open nesting birds it is also important bccause the presence of white droppings around the nest advertises its presence to predators.

Was this article helpful?

0 0

Post a comment