First, let me clear up an issue from my column last month. Due to a production error, my recommended measurement for the opening of a house sparrow-resistant bird box was erroneously changed from 1-1/8 inches to 1-1/2 inches. I suspect a house sparrow is working for the newspaper and made the change before the column went to press, because a 1-1/2 opening is an invitation to all house sparrows and more. The smaller opening of precisely 1-1/8 inches will exclude some desirable native birds, but it will allow house wrens, black-capped chickadees and oak titmice to enjoy a peaceful home without sparrows. I heard from a number of experienced and savvy readers on this point.
Speaking of size, there has been some fascinating research of late on the size of bird brains. Birds are anything but bird-brained. Work over the last four decades has shown them to have mental capacities equal to and often exceeding the abilities of mammals — especially in the areas of problem-solving and long-term memory. There are crows in New Caledonia that manufacture tools to extract insects from inside branches. And our Clark’s nutcracker can remember where it stashed a meal almost a year earlier.
Somebody, and I assume this to be a poor graduate student, had the task of dissecting the brains of a great number of bird specimens and measuring their size. Some of the patterns discovered are fascinating.
The brains of precocial birds are relatively smaller than those of altricial birds. Precocial birds are those that hatch with a full coat of down, open eyes and the ability to follow mom about and find much of their own food. These include species such as ducks, quail and killdeer. Altricial birds hatch blind and helpless, such as robins, sparrows and swallows. This, in itself, is interesting, but I will save the exploration of this discovery for another time.
It turns out migratory birds have smaller brains than those that are sedentary. When I first read this, it was the opposite of what I expected. It seemed that long-distance migrants certainly must have larger brains to find their way over hundreds if not thousands of miles. They must also be intelligent enough to find food and shelter and avoid the different predators in the various habitats they visit and reside in. Apparently not.
There are several potential reasons for smaller brains in migratory birds. First, brains are expensive. Ounce for ounce, they demand more energy than any other organ. Flying also demands considerable energy, and the long-distance flights required in migration tax the abilities of many birds. A smaller brain is energy-conserving.
Another possibility is that a thorough knowledge of the home of a nonmigratory bird is of tremendous value. As different foods become available throughout the year, knowledge of one’s territory allows a bird to know where to go and how to search for the best resources. The best nesting and roosting sites can be staked out. Knowing what potential predators are present is vital. Knowledge of one’s neighbors and the location of territorial boundaries is also a plus.
I now think differently of the brainy black-capped chickadee that lives along Bear Creek and the crafty scrub jays in my yard that stay year-round compared to the beautiful but apparently less brainy yellow warblers and black-headed grosbeaks that head to sunny Mexico for the winter.
I still think a winter vacation in the tropics is pretty smart.
Stewart Janes is a Biology professor at Southern Oregon University. He can be reached at firstname.lastname@example.org.