Expert: Roger Lederer - 6/8/2011

Question
About two and a half weeks ago I noticed a bird's nest with one egg in a hanging planter on my front porch.  The next day there were two, then three, four and then eventually five.  During the process and with some research, I came to conclude it was a House Finch nest.

Everything proceeded normally until about day 12 after the first egg was laid, when one egg completely disappeared, leaving four.  Two days later, I noticed one of the four starting to hatch, but when I checked back a few hours later there were two eggs left and one dead baby (so, either one egg went missing and the hatched baby died, or two eggs hatched and one baby went missing).   Later, I noticed the one remaining dead baby was gone.  There was never any trace of egg shells or dead babies anywhere near the nest or on the ground.

Over the next two days, the mother bird continued to incubate the remaining two eggs, and I was hoping the remaining two would survive.  Then, I noticed the mother was nowhere to be seen, even after watching for several hours to be sure.  I took a look inside the nest, and the two remaining eggs were covered in small bugs.  I had assumed the eggs had gone bad and that's why the mother abandoned them, then suddenly one hatched.  The baby bird has been left all alone in the nest, the mother is nowhere to be seen.  There is still one remaining egg, though I'm not certain yet if it will hatch.  Is there any chance the mother will return for the baby bird?  It has been over 12 hours since it hatched but still no sight of the mother, and I cannot believe it is still alive.

Assuming the mother bird does not return, I am not going to try to save the bird or the other if it hatches, but I want to know what went wrong.    Why did so many eggs and baby birds go missing?  The nest is in a spot that would be extremely difficult for land-based predators to reach.  Could another bird have been stealing the eggs and babies, which eventually led to the mother abandoning it?  Or, could my attention to the nest have disrupted the mother so much that she left?  I did pull down the planter to inspect the nest, but generally just once a day for a moment or two.  This, however, does not explain to me the nature in which so many eggs went missing, unless the mother removed them herself.  Any advise?  If I personally did something wrong, I want to make sure I don't repeat it!

Answer
Well, I can speculate as to what happened but I don't really know for sure. But I can tell you that this scenario is not unusual. Small birds' nests and eggs often get preyed upon and even more so with House Finches that nest around houses which tend to have mice, rats, and cats. You would be surprised how agile rats are. In addition, jays, crows, wrens, raccoons, opossums, etc. are all potential predators. The mother might or might not return for the baby bird. Sometimes it happens that the parents are eaten by predators. It's a touch life.  The chances of an egg making it to an adult bird are maybe 20-30%.
You probably didn't cause the whole problem, but any disturbance of the nest is a negative influence. You are a very big predator as far as the mother is concerned and with enough disturbance, she might say "the heck with this." So it's best to leave the nest alone. I've studied birds a lot and usually only checked the nests or eggs every 4-5 days.
Thanks for your concern.