Nature Notes: Winter in the Chihuahuan Desert

Winter has arrived in the Chihuahuan Desert. Fall colors abound, and temperatures are dropping. But the thing that really says “winter” is the stillness. The trill of the ground squirrel is gone as are the butterflies and lizards. Where has everything gone? 

Winter in the northern Chihuahuan Desert region is both cold and very dry. These climatic conditions make it difficult for plants and animals to survive.

For some animals, the answer is to migrate. Turkey vultures head south for the winter. As does the rufous hummingbird. 

Some butterflies migrate as well. The monarch butterfly is perhaps the best known of these. 
In the late summer, a generation of Monarchs emerge from their chrysalides. These Monarchs won’t mate or lay eggs until the following spring. All they want to do is find food and fly south, 3,000 to the mountains west of Mexico City.

By late September, all the Monarchs from breeding grounds east of the Rockies are funneling into Texas. The butterflies are headed for Mexico – a place that none have been before but that millions will find in November.

In the spring, as the days begin to warm, the monarchs will begin to head north, towards their summer breeding grounds to begin the cycle again.

Animals that don’t migrate need to find other ways to survive the cold, dry months. Some insects spend the winter as an embryo.
The preying mantid spends the winter in a hardened egg sac attached to a plant stem or rock. In the spring, the eggs hatch and hundreds of young mantids emerge.

Often their first meal is a sibling.

Other animals spend the winter in burrows or protected places. The pallid bat wedges itself into narrow cracks in canyon walls or buildings and hibernates.
Carpenter bees spend the winter in nest tunnels where they lay their eggs. 

In late August, the new adults emerge from their nests and begin to prepare to over-winter by gathering pollen and provisioning the tunnels. When the temperatures begin to drop, the carpenter bees huddle together in the protection of the old nest galleys. In April or early May, they emerge, mate and begin the cycle again.

Other animals, such as ground squirrels and lizards, hibernate in burrows underground. Their body temperature drops to only one or two degrees higher than the temperature outside. Their breathing slows and their heart beats only a few times a minute. Their bodies slow down so much they don’t need much energy to survive. The energy they do need comes from fat stored on their bodies at the end of the summer and early fall. In the spring, the animals emerge thinner and ready to eat!
As you explore the desert in winter, be sure not to disturb any hibernating animals that you find. Being rudely awakened causes them to use up their fat reserves faster, often leaving them without enough stored fat to survive the winter.

Nature Notes is produced by the Chihuahuan Desert Research Institute and Marfa Public Radio and is sponsored by the Meadows Foundation and the Dixon Water Foundation. Tune in to Nature Notes on KRTS-93.5 FM on Tuesdays and Thursdays at 8:35 a.m. and 4:45 p.m. and again on Thursdays at 7:06 p.m. Visit us online atnaturenotesradio.org.