COVID-19 measures ground usual snowbird migration

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Photo: Cartoon by Patrick LaMontagne

It is one of the mysteries of nature why some birds migrate and others don’t. In some cases, the answer is obvious. Hard to imagine a skinny blue heron surviving in the ice and snow; same for the hyperactive hummingbird. But why do sparrows and cardinals stay put while robins and juncos high-tail it south each fall?