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04/29/08
A Dumb Question About Deaf Birds
Filed under: General, Birding & Outdoors, Medical, Grandchildren
Posted by: Ken @ 12:32 pm

Our granddaughters seem interested in the structure of the feet of this newly hatched chick:

Of Hamster Livers and Starling Ears

In college, I majored in biology. This was a direct result of my childhood interest in birds and all living things. More properly, it was a result of the intense curiosity that is stimulated by even the most subtle aspects of the morphology and behavior of living things. Curiosity causes one to ask many questions.  Whether trivial or sublime, so many questions remain unanswered. I don’t know who said it, but it is so true: “The last thing a science learns is what it is about.”

A fact that intrigued me was that Golden Hamsters appear to be immune from the effects of the alkaloid colchicine, a mitotic poison that freezes cells in the process of dividing. The theory was that the hamster evolved in a region where the herb that produces colchicine is common. It somehow adapted and survived by developing resistance to the effects of the chemical. Many anti-cancer drugs also prevent multiplication of tumor cells, so I thought the lowly hamster might provide a key to finding how to selectively protect healthy cells from damage during chemotherapy.

I kept a colony of hamsters in the college lab, and fed them high doses of colchicine. They appeared to suffer no ill effects, although they did not reproduce while eating the colchicine-laced food. In order to test my hypothesis that the substance may end up being concentrated in a particular organ, I euthanized the animals, pooled their organs, and using a primitive glass column chromatograph, analyzed their tissues for colchicine. This revealed that the colchicine was indeed concentrated in their livers. Histologic examination revealed no pathologic changes in the liver or any other organs. It was an uncontrolled, poorly designed experiment without a clear hypothesis, that wasted the lives of innocent animals. I never learned why or how the hamsters resisted the effects of the poison. Since hamsters are normally exceptionally prolific, their failure to bear young appeared odd, as their body tissues exhibited normal cell division.

After I graduated, it was off to medical school, and that was the end of my experiment. It left me with more questions than answers.Today, an Internet search reveals much sophisticated research on the same subject.  For example, it was subsequently confirmed that the natural resistance of the Golden Hamster to colchicine is not manifested in the developing embryos in utero. Francis Crick had discovered the double helix of DNA only a couple of years before I executed my hamsters, but now the unusual resistance of hamsters to the erstwhile toxin has been explained at the molecular level. Resistance to colchicine has been found to be associated with specific DNA  sequences containing genes which alter plasma membrane permeability, leading to a decreased uptake of several anti-cancer drugs. Now, 55 years later, I cannot find any reference as to the applicability of this knowledge to clinical medicine.

Nieta watches as a Black Swallowtail butterfly emerges from its chrysalis:

The natural world is so full of questions. Before I retired, I traveled a great deal and spent lots of time at the Dallas-Fort Worth Airport. One day, in the mid-1970s, I noticed that European Starlings were feeding nestlings, whose heads popped out of nests located in crevices located where the jetways connected to the airport terminal’s walls. It seemed odd that the birds were exhibiting normal behavior in such a noise-filled environment. All the humans who worked in that area were wearing hearing protection. Yet these birds, of a species that is particularly vocal, seemed not to be suffering in the least. Surely, their sensitive ears must have been severely damaged by all those decibels.

Humans can adapt to hearing loss, through gestures, sign language and writing. Birds appear to rely heavily upon the subtleties of calls and songs, especially in their reproductive behaviors. Owls are known to locate prey by hearing alone. How did those starlings manage to rear their families amid the constant roar of jet engines? Incidentally, Killdeers were often present along the taxiways and landing strips– was it possible that they, too, were able to breed under these circumstances?

Internet research now provides me with an appreciation of the fallacy of anthropomorphising, of applying human attributes to birds. Just as my earlier assumptions about sex-linked characteristics in Muscovy Ducks proved to be 180 degrees away from the truth (I had falsely assumed that male sex was determined by the male parent, as in humans, whose males are heterogametic), I now know that the inner ears of birds, and most reptiles and mammals, have a unique regenerative ability to recover from damage to the microscopic auditory hairs (cochlear cilia) that are so essential to normal hearing. This fact was discovered by medical researchers who were looking for a cure for human deafness. Indeed, we humans are the oddballs in this respect.

Research conducted at the Laboratory of Comparative Psychoacoustics in the Department of Psychology at the University of Maryland in College Park, MD explores the issues of the effects of noise on bird behavior. Remarkably, they have discovered that birds have the ability to block out or mask certain background noises and still hear the calls of others. The following is from an abstract entitled  The General Effects of Noise on Hearing in Birds

“A great deal has been learned over the last several decades about the effect of noise on hearing thresholds in both humans and animals including birds. One useful measure, the critical ratio (the ratio of tone intensity to noise intensity expressed in decibels), tells us how loud a pure tone must be to be detected against a background of broadband, white noise. The critical ratio is the level of the pure tone at threshold (in dB) minus the spectrum level (dB per Hz) of the noise.

“Critical ratios have been measured in the laboratory for a number of species of birds including: budgerigars, canaries, starlings, song sparrows, swamp sparrows, red-wing blackbirds, cowbirds, great tits, cockatiels, and barn owls. In general, the effect of white noise on hearing thresholds in birds (as well as in humans) doubles with every doubling of frequency. In other words, the critical ratio at 2.0 kHz is 3 dB higher than the critical ratio at 1.0 kHz. However, some birds, such as budgerigars, show a remarkably different masking pattern… [suggesting] that budgerigars hear better in noise than other birds at frequencies between 2-4 kHz. Importantly, these laboratory studies of masking by noise can also be used to make predictions about how environmental or anthropogenic (human-made) noise affects the abilities of birds to hear each other in the real world… “

My question about the starlings remains essentially unanswered. In this one narrow area, such unanswered questions abound. Following are some suggested areas for future research, excerpted from the UMD Web site,  The Effects of Environmental Noise on Communication in Birds.

“…When noise masks the biologically important signals of birds in the wild, and interferes with their ability to communicate effectively, it surely has a detrimental effect on their normal behavior and breeding biology…

“…There are virtually no data published on the effects of different types of noises (e.g. traffic or aircraft noises) on the perception of species-specific vocalizations. Such laboratory data are critical for understanding the effect of noise on acoustic communication and for developing reasonable guidelines for noise abatement…

“… It is important to understand that intense traffic or aircraft noise probably represents a substantial risk to normal acoustic communication in birds. It is not practical to think of eliminating the detrimental effects on communication completely. It is practical, however, to try and quantify the risks so that intelligent judgments can be made concerning the extent to which noise may interfere with the normal behavior and breeding biology of birds in the wild, and reasonable arguments can be made about how much risk is acceptable. At present, predictions made for detection of vocalizations in the environment only address the simplest case, the ability of a bird to tell whether a sound occurred (i.e. detection). Such a measure does not reflect a bird’s ability to communicate effectively in a particular acoustic environment, and may have little bearing on it…

” …At the present time, these worthwhile environmental projects are not funded. The ultimate goal of these studies is to generate a predictive model for evaluating the impact of noise on acoustic communication in birds in order save endangered species…”

One Response to “A Dumb Question About Deaf Birds”

  1. Janine Says:
    Fascinating entry, Ken.

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