Under a Snowy Blanket
It’s been an unusually snowy year, and you might wonder how small animals like field mice manage. Surprisingly, snow helps them survive. When the snow blanket is at least six inches deep, it keeps the ground underneath at a stable temperature even when the air dips below zero. Voles and mice tunnel under the snow, seeking seeds and avoiding the watchful eyes of predators.
The Shelf Life of Acorns
Picky gray squirrels make their acorn caches last longer. They can choose between white oak and red oak acorns. White oak acorns take two seasons to become fertilized, which gives them a longer shelf life. Red oak acorns sprout more quickly. Sprouting uses up about half the nutrients in the acorn and compromises freshness. Squirrels somehow know to eat the red oak acorns first and save the white oak acorns. When they do store red oak acorns, squirrels pull the little oak embryo out of the acorn’s tip to keep it from sprouting.
See this study from the journal Evolution.
Now, Where Did I Put That?
Birds hide seeds and nuts for winter. To do this, they form a mental map of up to 20,000 locations! Black-capped chickadees, zebra finches, mountain chickadees, nutcrackers, jays, and starlings all grow new brain cells as the days get shorter and colder. Those new brain cells help them map the hiding places of their seeds.
How does this work? The changing weather triggers birds to secrete more of an enzyme called aromatase, which changes testosterone into estrogen. Estrogen derivatives make the brain more flexible and aid in memory.
See this story by Robert Krulwich in National Geographic, this story by Betsy Mason in Knowable, this story by Rachel Adelson for the American Psychological Association, this study of zebra finches in the journal Neurobiology of Learning and Memory, this study in the journal Hormonal Behavior, and this study in the journal Endocrinology.
Waiting for the Cold
Pygmy owls in Finland are adapting to climate change by waiting until later in the year to start building their food caches. As fall weather is warmer and wetter than in the past, food hoards are likely to rot if started too soon. Pygmy owls have adapted to this situation by delaying food hoarding.
See this study in the journal Global Change Biology.
Here’s a weird way of adapting to the cold. A hummingbird found in the Andes Mountains survives cold nights by going into a dormant state in which it’s frozen almost solid. Its body temperature drops to 37.8 F, and its heart rate slows to 40 BPM. To a casual observer, the birds appear dead. But when the day warms up, they revive and go about their business.
See this story by Jonathan Lambert in Science News.
Living Food Caches
Many wild animals store caches of food to see them through the winter, when food may be less readily available. But it’s not all seeds and nuts. Shrews, moles, and fire ants all capture their favorite prey and immobilize them without killing them. This gruesome practice keeps their meat from spoiling during multiple freeze-thaw cycles. Then they’re available for a mid-winter snack.
See this story by Liz Langley for National Geographic.