Why do baby birds disappear?
One of my regular readers recently asked the question: “Why do baby birds disappear?” We had been corresponding during the recent height of the Australian breeding season. Spring here is coming to a close, but many birds are still actively making nests, sitting on eggs or feeding young in the nest or just out of the nest. This reader observed that many baby birds go missing. What happens to them, she asked.
Here is my reply:
It is very distressing for bird lovers to see the little birds disappear or be killed in some way so soon after hatching or leaving the nest. If we knew the figures, I think we would be horrified by the enormous attrition rate in our fauna, not just birds.
Some possibilities include the following:
1. Removal from the nest by cuckoos. We have several species of cuckoos in Australia. The female lays one egg in a host nest. This could be a thornbill, honeyeater or a range of other species. The host bird hatches the eggs and the baby cuckoo hatches first and it removes all other eggs in the nest in the first hour or so after hatching. It then gets ALL the food from the host parents. Harsh yes – but this is normal, natural cuckoo behaviour.
2. Predation of eggs or chicks: this could be from ravens, crows, currawongs, butcherbirds, hawks and even magpies. Cats, foxes, snakes and lizards, especially goannas, will also raid nests.
3. Predation out of the nest: Once fledged and out of the nest the young birds run the gauntlet of so many hazards including all in number 2 above. Add to those hazards the problem of being hit by speeding cars, wild storms, flying into glass panes (very common), captured by well meaning people and not cared for properly, heavy rain, cold nights and so on.
It is a wonder that any survive at all, especially in urban areas. This is in part compensated for by the following strategies:
(a) Laying 3-5 eggs for each clutch as this increases the success rate
(b) cleverly camouflaging the nest – with all my experience I am still fooled by their cryptic nest sites.
(c) breeding two or three times in one season.
It would certainly help if all cat owners were responsible and made a run for their animals. This would eliminate some deaths in our fauna, but a far greater problem is the feral cats. There is no control of these and all are very big, strong and cunning. I think compulsory desexing of cats is the way to go, but it would only be a start. Catching all the feral cats is probably not feasible. Making sure no more are added to their ranks will be a good start though.
- Common Blackbirds – the article that started it all. The many comments are very interesting reading.
- Do Blackbirds Swoop? How to deal with aggressive bird behaviour – another article I wrote about Blackbirds. This one also created a great deal of interest with many interesting comments.
- Magpies behaving badly – Australian Magpies have a bad reputation during breeding season.
- A bit on the nose – an amusing incident involving a cyclist, a swooping Red Wattlebird and a nose.
- Anyone for a swim? Forget it baby Blackbird. Now this is something different.