About six years ago the robins vanished from my town. This was well before West Nile Virus took away all my crows so I didn’t know who or what to blame. Wife suggested it was because of something people put on their lawns but whatever the cause the robins are back in force!
Why? Why might they have gone away in the first place?
It could be a cyclical population thing; the classic one is foxes and rabbits; the rabbit population increases because there aren’t many foxes, but this provides more food for the foxes, so the fox population increases (lagging behing that of the rabbits), but because there are now so many foxes, the rabbit population stops increasing and then sharply declines, leaving the foxes to starve; , but now that there aren’t many foxes…
In real life, it is nearly always a lot more complex than that, but it sounds like in your case it will be the result of a recent increase in the abundance of their favoured foods, or a decline in the number of their primary predators, or both.
Where do you live? That’s always a key item of information in questions like this.
Just a note on this topic. I grew up in northeast Ohio, and robins were one of commonest birds around. I moved to Houston, and never saw one for 15 years. About 5-6 years ago I started seeing a few, and in the last couple of years they’ve become fairly common here, too, though nothing on a par with our most common birds. Some of them hang around through the summer, though most move on. I don’t know what a respectable migratory bird like a robin is doing hanging around this hothouse.
Oh, and I have yet to see a female here.
It’s funny with birds in general. Not once during my first 26 years of life, did I ever see a crow. Crows and ravens were something I knew only from stories, like the poem by Edgar Allen Poe. I had lived mostly in L.A., with briefer sojourns in San Diego, Gottingen (Germany), and the upper Midwest. But not once had I ever seen a crow.
Then one day, in 1984, I saw a crow in the San Fernando Valley. I was reporting for work on the first day at a new job, and as I walked in, I heard, “Caaaaaaaawwwww!!” And since then I’ve been seeing more and more.
A western suburb of Chicago.
And had there been a decrease of the population I’d’ve guessed something along the lines of what Mangetout said but here it was a near elimination of the population with no reductions or great increases of the birds that fill a similar niche. And there was no visible change in the predator population, either.
Were you actually looking for robins, or did you just not happen to see any? If they took a sharp population plunge, but weren’t actually locally wiped out, you probably wouldn’t have seen any if you weren’t out there with binoculars and a floppy hat. (OK, maybe you might have seen one without a floppy had, but all the birders I’ve ever seen seem to wear 'em.)
Spectre of Pithecanthropus, was this an ominous sign of things to come for your new job?
According to the Stokes field guide, robins are found year round in all of the USA except for the area roughly north of Cenral Illinois, which includes NE Ohio, wherein they are found only in the summer. However, when I lived in Peoria, Il, I saw some robins in the winter also. I now live in Charleston, SC, and it was said that robins do not nest here, but I saw robins with nesting material years ago. It has finally been realized that they do, indeed, nest here.
But it is funny with birds. For over 10 years noone here saw a purple finch. House finches galore, but no purple. This year they have been common, but not as common as the house. That could have been caused by the abnormally cold weather in the north. About 15 years, dickcissels were seen here, but not since. Stokes does not show them being found here at all.
While most states have common robins all year long, there are numerous subspecies that will experience a population explosion every 40-50 years depending on a complex interaction of environmental factors. Further, the increased population density of an individual type of bird will elicit unexpectedly violent group behavior with minimal provocation–much like what is seen in Africanized "killer"bees. Some old-timers may recall the bizarre robin plague of 1963 which decended on Bodega Bay, California during which numerous bird-related fatalities were reported.
Several theories have been advanced for these population explosions, ranging from cyclical erthworm population variances to other man-made environmental factors, and while no study has ever proven to be conclusive, the real cause is likely to remain a mystery given that this is a relatively rare phenomenon.
Well, I’m speculating, but one guess would be severe weather that could have knocked out a migratory or wintering flock all at once. If the birds from your town were all part of the same flock, a severe storm could have wiped out a big percentage of them all at once, possibly in an area some distance from where they spend the summer.
Some kind of chemical on lawns could be a possibility, but it would have to be pretty universal in the area to have eliminated the robins nearly completely. However, the chemical need not have killed robins directly, but could have affected numbers of worms or insect larvae available in lawns for feeding young.
I don’t think it’s likely that an increase in predators killed them off. Robins survive fine in areas teeming with house cats.
Re crows, American Crows have been adapting more and more to the urban landscape. They are (or were, prior to West Nile) much more common in my neighborhood in the Bronx than they were when I was growing up in the 1950s.
Re purple finches, many finches and other seed eaters are known as “irruptive” species, that is, severe winter weather periodically drives them down from their usual northern wintering areas so that they appear in large number far south of their typical range.
Robins live on bugs, worms, and larval critters in the ground. Perhaps climate conditions or something have been very good for ground bugs this year.
Are they round? Round robins propogate in tournaments. 
I saw a documentary about that! Don’t mess with me, son. I’m pretty hard to “whoosh.”
Maybe the crappy economy has caused fewer people to pay extra for lawn services and there are more bugs to eat. Whatever the cause, I’m glad they’re back. I look for them and it makes me happy to see them.
I saw a few crows a couple weeks ago but they’re gone, but we’ve also had the first report of one killed by West Nile in the next town south of here. I really miss my crows. They were silly! A crow once came up to me in a parking lot a couple miles from home. It was begging like a baby, which is what they would do to my wife who used to toss them grubs and slugs from the garden. I wonder if it was one of “ours” and it recognized the car?