Environmental Variables and the Nightly Emigration Ratio of the Robin (Erithacus rubecola) on the Island Hjelm, Denmark

Several weather factors, and the number and weight of the resting Robins were investigated for influence on the subsequent nightly emigration ratio, which was taken as an appropriate measure of “migratory readiness.” Cloudiness influenced the emigration ratio in a negative way, and the number and weight of the birds influenced the emigration ratio in a positive way. Contrary to expectation, a following wind in the “standard direction” was found to be of no significant positive influence — the sign of the correlation was even negative.