Bird Watcher's General Store

Can Birds See In The Dark?
10/05/12


Dear Bird Folks,

I’d like to know more about birds’ vision. Specifically, I’m interested in how well they can see at night. This summer we had a nest next to our back door. Sometimes we’d forget and use that door at night, causing the startled mother bird to fly off into the dark. I worried about her finding her way back to the nest in the dark. Is that a problem? –Carol, East Hartford, CT

First, I have a question for you, Carol,

Do know how the city of Hartford got its name or do you only know stuff about East Hartford? I was watching Jeopardy on TV last week and there was a “question” about Hartford. (I know Jeopardy has that weird thing where Alex gives us the answers and we provide the questions, but you understand what I’m talking about.) The question suggested that the name Hartford had to do with deer because male deer are apparently called “harts.” But I’ve always heard that Hartford is named after Hertford, England. Could you look into it and get back to me? I haven’t slept all week wondering about it. I worry about strange things.

Of their senses, birds’ eyes are the most important. With very few exceptions, birds see better than they hear, smell or taste. On average, birds’ vision is better than humans’ (and a million times better than those NFL replacement referees). Birds’ eyes are disproportionately large and take up so much room in their head that there is no room for extra muscles, so their eyes are fixed in their sockets. If a bird wants to see something, it must move its entire head. Birds can’t even roll their eyes to express their disgust when they’re annoyed or hear a bad joke, which is lucky for me.

Exactly how well birds can see is the subject of much debate. Because of the language barrier, researchers are never sure which line on the eye chart birds are able to read. The bigger problem is that there are nearly 10,000 different species of birds in the world, all with different levels of vision so it’s hard to generalize. Hawks have laser-sharp diurnal vision, while owls see better at night and ducks see better underwater. And let’s not forget about peacocks. Have you seen all the eyes they have?

I don’t want to turn this column into a middle school biology lesson, but in case you’ve forgotten, eyes contain rods and cones. Cones are important for viewing objects in color and birds’ eyes are packed with them. This gives birds excellent color vision and makes them big fans of the Retina Display on the new iPhone. Why do birds need to see in color? In addition to enjoying the iPhone, color vision undoubtedly assists them in finding food, especially when selecting which flowers have the most nectar or which berries are ripe. And then there’s the whole mating thing. Many birds, particularly the males, use colorful plumages to attract a mate. If the females couldn’t see color there would be no need for, say, male bluebirds to be blue or male cardinals to be red. How boring would that be for us? Cardinals wouldn’t be very interesting if they were all brown, and getting a visit from the “gray bird of happiness” would not be nearly as exciting.

While cones are great at detecting color, they don’t work as well at night. So owls have relatively few cones, but instead have extra rods, which are sensitive to dim light. The abundance of rods allows owls to have excellent night vision, but fewer cones means that owls are most likely colorblind. Being colorblind might seem like a bad thing, but the owls are okay with it. The males don’t need to grow flashy feathers to impress their mates. Plus, they save tons of money each year by not having to buy red roses on Valentine’s Day. Any color roses will do.

Having eyes with extra rods doesn’t mean owls can’t see during the day, because they can. It also doesn’t mean that the cone-filled songbirds can’t see at night. They just don’t see as well as owls do. In fact, lots of non-owl birds are active at night. Songbirds make their long-distance migrations under the cover of darkness. Shorebirds feed when the tide is right and it doesn’t seem to make much difference to many of them whether it’s daytime or nighttime. And let’s not forget about carrier pigeons. They’ll fly anytime, not just nine to five. The unions haven’t gotten to them, yet.

I wouldn’t worry too much about the mother bird you startled from a sound sleep, Carol. I’m sure she quickly found her way back to the nest. Even though songbirds don’t see perfectly at night, they see well enough to get by. And speaking of being startled during a sound sleep, birds sometimes are the ones that do the starling. I’m occasionally awakened in the middle of the night by the sounds of Great Blue Herons fighting near my house. If you’ve never been disturbed by croaking blue herons you are missing quite a treat. They sound like a cross between a rabid camel and a cat coughing up a fur ball. One time the herons were so loud they woke up my wife (which is nearly impossible to do). I just told her that she woke herself up snoring and she went right back to sleep. As for me, I was awake for the rest of the night…wondering about that Hartford, Hertford, deer thing. Curse you, Alex Trebec.




Artwork by Catherine Clark


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