Dear Answer Man, I know you're an expert in everything, so enlighten me regarding something I've always wondered.

There are rock bluffs and cliffs all over the area, of course, and a lot of the time, those rock cliffs are peppered with holes. Are those naturally occurring holes or do birds somehow make them? I'm assuming it's not woodpeckers ... maybe rockpeckers? -- Anonymous

This perplexed reader also referred to a specific location -- a cutbank of St. Peter sandstone at the junction of Goodhue County roads 24 and 25 in Cannon Falls.

Like most sandstone, the St. Peter variety is relatively soft and just right for bank swallows (in Latin, the beautifully named riparia riparia) to peck out little nesting burrows. They always nest in colonies, which is why those particular cliffsides look like Swiss cheese.

Why does Swiss cheese have holes? That's a question for another day.

The Answer Man's brain is riddled with mostly useless information. Send questions to P.O. Box 6118, Rochester, MN 55903 or answerman@postbulletin.com.

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