Q. Why don’t birds get infected when drinking feces-contaminated water in birdbaths?
A. “Why do you think they don’t?” said Kevin McGowan, an ornithologist at Cornell University. “I’m sure there is some disease transmission.”
Birdbath owners should try to keep the water clean, especially if a sick bird shows up, but some contamination is inevitable, he said.
This risk is minimal for most birds, however, as they do not really spend much time at a birdbath, McGowan said. For birds that patronize most feeders and birdbaths, the benefits outweigh the risks.
Many birds do have powerful protection from infection when it comes to eating rotten and possibly diseased foods. Buzzards and other birds routinely consume carrion, for example. One way they handle the risk is simply to digest pathogens, including viruses and bacteria. It is rare for an organism to be both indigestible and pathogenic.
How cats see in the dark
Q. Does the slit shape of a cat’s pupil have any advantages over the more rounded pupils of other animals?
A. “There are significant advantages,” said Dr. Richard Goldstein, chief medical officer of the Animal Medical Center in New York City. “A cat can quickly adjust to different lighting conditions, control the amount of light that reaches the eye and see in almost complete darkness,” he said. “Moreover, the slit shape protects the sensitive retina in daylight.”
The slit-shaped pupil found in many nocturnal animals, including the domestic cat, presumably allows more effective control of how much light reaches the retina, in terms of both speed and completeness.
“A cat has the capacity to alter the intensity of light falling on its retina 135-fold, compared to tenfold in a human, with a circular pupil,” Goldstein said. “A cat’s eye has a large cornea, which allows more light into the eye, and a slit pupil can dilate more than a round pupil, allowing more light to enter in dark conditions.”