Gamma Radiation Effects on Nestling Tree Swallows

Abstract

The sensitivity of Tree Swallows (Tachycineta bicolor) to the stress of ionizing radiation was investigated with growth analysis. Freshly hatched nestings were temporality removed from nests, taken to the laboratory and acutely exposed to 0.9, 2.7, or 4.5 Gy gamma radiation. Some of the unirradiated control nestlings were also taken to the laboratory, whereas other were left in the nests. Growth of all the nestlings was measured daily and analyzed by fitting growth models. There was no detectable radiation—induced mortality up to fledging, °20 after irradiation. Radiation exposure did not affect the basic growth pattern; the logistic growth model was most suitable for body mass and foot length, and the von Bertalanffy model for primary—feather length, irrespective of treatment. Parameter values from these models indicated pronounced growth depression in the 2.7—Gy and 4.5—Gy groups, particularly for body mass. Radiation also affected the timing of development. The growth depression of the 2.7—Gy group was similar to that cause by hatching asynchrony in unirradiated nestlings. The 4.5—Gy nestlings grew as well as unexposed nestlings that died from natural causes. Chronic irradiation at °1.0 Gy/d caused more severe growth effects than acute exposure to 4.5 Gy and may have caused permanent stunting. Growth analysis is a potent tool for assessing man—made environmental stresses. Observed body—mass statistics and model parameters seem to be most sensitive to environmental stresses, but coefficients of variation are not necessarily correlated with seabirds. Unfortunately, growth analysis may fail to assess the full impact of the stress, because stress factors can have effects far beyond the initial growing period.