Relative Sensitivity of Nestlings
of Wild Passerine Birds to Gamma Radiation

 

W. K. Willard

 

Summary

Two or three nestling bluebirds (Sialia sialis) or crested flycatchers (Myiarchus crinitus) were removed from nest boxes located within the U.S. Atomic Energy Commission’s Savannah River Plant reservation, one or two of which were irradiated by a cobalt-60 source while the remaining nestmate sibling served as a non-irradiated control.  All nestlings were returned to the box as soon as possible and their development to the fledging stage observed under natural conditions of care by their parents.  Nestlings were irradiated at either two days of age (cold-blooded stage) or nine days (warm-blooded stage) with single acute doses ranging from 100 to 3,000 roentgens.

The lethal dose for both ages of bluebirds was 3,000 roentgens and the estimated lethal dose-50 for the 16-day nestling stage about 2,500 roentgens. However, severe stunting effects on growth and feather development occurred at such lower doses, reducing the chances of survival in transition from nestling to the fledgling stage. Nestlings irradiated at two days old at the level of 300 to 500 roentgens were smaller and had on the average shorter primary feathers at the tine of normal fledging by about an average of 10 percent as compared with control nestmates.  These differences were statistically significant.  At
1,500 or 2,000 roentgens the stunting of growth and feather development averaged sore than 50 per cent.  From the data at hand it was estimated that the lethal dose-50 for transition from nestling to fledgling stage would be about 500 or 600 roentgens (or about one-fifth the lethal dose) for birds irradiated early in development.  Effects were less severe in nine-day birds since weight gains and feather development were well along by this age; however, shortening of primary feathers occurred at the higher doses (about 2/3 feather elongation occurs after nine days).  One nine-day bird irradiated at 500 roentgens was known to survive to adulthood and to breed normally the following year.

Nestling bluebirds living under natural conditions proved to be more resistant to gamma radiation than young chickens.

Preliminary data on the crested flycatcher suggested, but did not prove, that nestlings of this species were more sensitive than bluebirds to the lower levels of gamma radiation (300 to 600 roentgens).

All nestlings which survived irradiation developed normal fledging behavior and attempted to leave the nest box along with normal young even when growth and feather development an greatly stunted. Nestlings receiving up to 800 or 900 roentgens at two days of age were usually able to leave the nest at the normal time, but, as indicated above, their chance of survival during the critical fledging period was reduced by their weakened condition and subnormal flying ability. After receiving 1,500 roentgens nestlings were usually able to climb out of the nest box at fledging time but were unable to fly even though they made every attempt to do so when the normal siblings fledged. It was clear that while sub-lethal doses markedly affected the growing tissues of the body and feather follicles, such doses did not affect the brain centers responsible for the development of ontogenetic behavior patterns.

 

 

 

Willard, W.K. 1963. Relative sensitivity of nestlings of wild passerine birds to gamma radiation. In First National Symposium on Radioecology, edited by V. Schultz and A. Klement Jr. New York, NY. Reinhold Publishing Corporation.