Walking through the woods in a graupel shower this afternoon prompted me to do a little more research on the phenomenon. Just what is graupel, anyway, and how does it differ from other forms of frozen precipitation?
The Dec 24 2020 edition of the Daily Interlake has a useful downloadable supplement (by Scott Heisel of the Lake County Leader) on winter birding day trips in the Flathead Valley and beyond. It’s a little difficult to locate, so if you missed the print edition, here is a PDF file of the article.
Many birds migrate from a winter home to take advantage of an abundance of insects, longer periods of daylight for scavenging, and increased success in raising a brood in the north. As winter arrives and insects become scarce their survival depends on their returning to a warm climate where insects are available. Birds that depend on non-insect food sources and move from place to place in response to the availability of food sources, independent of season, are referred to as nomads. They often travel in flocks of the same species, searching out food, and moving on.
The sight of a Mourning Cloak butterfly is a sure sign of spring to me! In late fall, they crawl behind loose bark on a tree where they increase the level of glycerol in their blood, convert excess water in their bodies into a gelatin-like substance that doesn’t freeze, and spend the winter. As spring warmth arrives, they reverse those properties and start flying sooner than many others! Many butterflies endure the winter as eggs, caterpillars, or in a chrysalis. A few, like Monarchs, migrate to warmer climates.
It’s fall already; raptor fans have been counting the migrating raptors at various mountain top sites for a few weeks, and I’m already noticing fewer soaring birds in the West Valley. Any day we may see Rough-legged Hawks that have migrated thousands of miles to call this home for the winter.