Synopsis: When I moved a feeder just 18 inches from its original location birds continued to fly to the old location. They would drop almost to the ground when the feeder failed to be where they expected it. Then they would retry with the same results. Eventually, some learned the new location, but it took several tries and an expeditionary trip.
We live in a townhouse community and the extent of our back yard is just a yard/garden area that covers approximately 10 feet by 24 feet in area. This yard area is separted from the house by a 16x12 patio and a 8 x 12 utility room. The entire patio and courtyard is surrounded with a six foot high painted board fence. If we want to do something outside, it must be done in this tiny area.
Last year, I put up a screen room on the patio. To entertain myself I put an iron post suitable for holding four bird feeders in the yard not too far from the fence. A cylindrical feeder with a tray at the bottom was the favorite of the larger birds such as cardinals, bluejays and cowbirds. Things went well for a few days, but soon we found squirrels hanging off the feeder. We watched for a while and learned they could easily climb the metal bar.
So we put Vaseline on the pole and solved that problem for a few hours. The squirrels would attempt to climb the pole, but they ended up sliding to the ground. However, the next day, we discovered the squirrels hanging upside down from supports of the feeder dumping the seed on the ground. When we appeared, they jumped from the pole to the fence, sometimes nearly missing it.
Anyone who feeds birds know that squirrels are determined and smart. So we watched them a day or two and decided to grease the support they were landing on. This also worked for a few hours. They would continue to jump, but the greasy support didn’t allow enough grip for them and they would fall unceremoniously to the ground.
A day or so later, though, we watched them as they had learned to just allow the slide to occur down to the feeder hook and then they would use the feeder as the place to grip. Greasing the feeders wasn’t a viable option. Birds were already having a hard time when they landed on the greased support, so if we put vaseline on the feeder, it would make it impossible for them to be able to use it.
So we watched the squirrels some more. We realized that the jump from the fence to the feeder was just about the absolute most distance they could accomplish. In fact, it was a struggle for them to reach that distance and to hang on. We reasoned that if we moved the feeder a little further from the fence (and closer to the house) they might not be able to jump from the fence to the feeder and our problem would be solved. Remember that our yard is small, so the most we could move it was 18 inches in a straight line toward the house. It’s alignment with the surrounding fences and sidewalk remained the same.
This solved the squirrel problem. But in the course of moving the feeder, we had inadvertently set up a revealing bird experiment.
When birds come to our feeder, they rarely fly directly to it from some distance away. Instead, they land on the fence (or the courtyard tree), check out the courtyard, size up the feeder location, and then fly to it. I speculate that they are verifying everything is safe which might be difficult for them to do from the sky.
The larger birds favored a mixed seed feeder which was cylindrical with a plate on the bottom to catch loose seeds. They would come to the feeder, and land on the plate. Then using their beaks, they would scrape seed from the seed ports on to the plate. By doing this, they had much better balance than they would have if they had used the tiny perches and they could sort through the seeds to pick out the ones they wanted. The plate offered a much larger landing area as well.
Although we had moved the feeder 18 inches closer to the house and away from the fence, all the feeder cylinders remained in their same relative positions.
As soon as the feeder was moved, something surprised us. The birds would fly toward the feeder but instead of landing on it, they turned too soon. It would take an instant for them to realize that the feeder wasn’t where they were landing and they would drop almost to the ground before they recovered to flight. Then they flew back to the fence, turned around and looked out across the court yard. They turned their head and looked with first one eye and then the other verifying that, sure enough, the feeder really was there. Both eyes saw it.
And then they would try again with the same results.
After two or three tries, some birds flew off to other places that didn’t have these kinds of problems.
Some tried another option. They tried again, but instead of trying to land where they thought the feeder should be, the continued to fly until they flew past the feeder in its new location. Then they turned and flew back to the fence. After doing this once or twice, they flew successfully to the feeder and landed without incident.
The first time or two that we saw this, we were startled and didn’t know what was happening. But after several birds had done this, we realized that they were attempting to land at the feeder’s old location–which I call the phantom feeder.
And this got me to thinking:
We know that birds have their eyes on the sides of their heads and therefore cannot see directly in front of them (Which is why they turned their heads back and forth when re-examining the feeders from the fence).
(The following is speculation)
Birds apparently do not turn their heads when they are flying, but instead, use landmarks to either side to determine their location.
When they saw the feeder from the fence, they didn’t have sufficient depth perception to realize that it had been moved. So they must have flown to where the landmarks told them the feeder would be and then turned into the feeder to land. When their was no support, they flew back to investigate from the fence. You can imagine how puzzling it would have been to see something but for it not to be there…or so it would seem. The birds that flew off could not rationalize this situation.
The birds which eventually flew past the feeder were gathering new landmark coordinates. They realized that their mental map was no longer correct.
And this caused me to realize just how different the perspective of a bird must be. When we are heading toward something, we can maintain a view of it and judge when we are getting there. When a bird approaches something, it can see virtually everything around EXCEPT what it is heading toward. Birds with eyes to the side must carry a mental map of the location of things by what lies to either side.
When you think about how many things we change in the courtyard (such as the placement of buckets and hoses and other assorted things, it is pretty impressive that they have singled out the essential stationary things and discard all the other movement “noise.”
These websites address the issue of sight in birds but don’t specifically address locating an object in a small field of operation.