Friday, May 23, 2008

Birds Loose Their Mates Also

Birds and people have similar problems such as losing their mates through death or desertion. When this occurs it places a demanding burden on the surviving mate, whether bird or human.

A fellow bluebird enthusiast, Ann Sawyer, called to report that she found the nestlings of one of her bluebird families dead in the box when she monitored it.

She has seen neither parent since finding the young dead. The nestlings were about a week old.

Her question.

What could have caused the death of the baby birds? It could be they were fed by the parents worms and insects that had eaten a diet of pesticide sprayed foliage. This might be confirmed if the parents return to the box after it is cleaned out and start another family.

If the parents have truly disappeared, most likely they were killed because bluebirds don't commonly desert their nestlings. If one is killed, or flies away from its responsibilities, the other takes over the job of rearing the young until they are able to care for themselves.

Generally, female bluebirds start another nest almost immediately after the young leave the nest. The male then takes charge of the fledglings, feeding them and guiding them in selecting their own food, protecting them until they fly well. The parent birds of the dead brood might have already moved away from the disaster and started a new nest.

It is well to remove the nest as soon as the young fledge. On our bluebird trail, we observed that if it was not removed, often the pair would build a nest on top of the old one bringing it almost to the level of the opening. We found starlings, house sparrows, 'possums, raccoons or other predators could reach their dirty paws or claws into the nest and pull out the eggs or young and destroy them. This happened several times on our trail.

There was a couple who discovered one of their bluebird boxes on the ground and all but one egg gone. The husband secured the box back to the pole. A new nest was built and five eggs laid. The culprit returned and stole the second clutch of eggs without damaging the nest. They decided they needed a metal-mounted box.

Erecting a new box about six feet from the old nest and pole, they removed the nest from that box and put it in the new one. The bluebirds sat on the wire overhead and watched and cheered and hurrahed.

Three days after changing boxes and putting the nest in the new box there were two eggs in the nest. In time, a clutch of five eggs was laid.

These experiences point out how little bluebirds are disturbed by human contact. On our trail, when we found the female on the nest we quickly closed the box. We didn't try to count the eggs. We observed that if the hatching date was near, the mother would not leave but would sit tightly on the eggs. If incubation had just begun, she flew away as we touched the box.

The late T. E. Musselman pointed out that during 40 years of working with thousands of bluebird broods, he had never seen a bluebird desert a nest because of monitoring. Even some, he wrote, didn't leave the nest while he checked the eggs beneath her.