Rufous Migration
By arriving first, earliest males have choice of best territories, improving chances of attracting females for breeding. They must balance this advantage with arriving before there is plentiful food available.

Females find more flowers on the spring migration route if they leave a bit later. Hummingbirds do not form pair bonds, so females are more valuable than males for breeding and thus reduce their risk by waiting for a reliable food supply.

Adult males leave breeding ground earliest (typically mid-July), which may leave a richer diet for the adult females and developing young.

Rufous Hummingbirds must double their body weight in order to fuel their migration.

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