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A study of the seasonal variation of circulating immunoreactive hormone (ir LH) was undertaken in captive Herring gulls (Lams argentatus) by estimating the hormone concentration in monthly plasma samples with a radioimmunoassay to chicken LH.

In the mature gulls (in 4th or 5th year), the ir LH concentration increased significantly through the spring (from 0.71 to l.94ng/ml in males and from 0.59 to 2.34ng/ml in females). The ir LH peak in the females may occur marginally later. In younger birds, only a slight elevation of the hormone level was apparent. A subsequent small summer peak of ir LH was found only in mature male gulls. Another major feature of the annual secretion pattern was the dramatic increase found in all groups of gulls in the sample taken at the end of November. This level had fallen to near basal values only a month later in all birds except the mature male gulls.

Throughout the winter, spring and summer, the circulating ir LH in the immature birds remained below that found in their mature counterparts.