What happened to the birds during the big freeze?

At 6 a.m. every morning during winter storm Uri, I trudged outside on snow and ice to fill my bird feeders.

Hey folks, I was born in Houston, not in Bangor, Maine. But migratory birds, like yellowrumped warblers, which may likely have been born in Bangor, hightail it to Houston for mild winters. What a cold shock for them to find a thick layer of snow in my yard.

I quickly filled sugar water feeders for a rufous hummingbird that has claimed our yard for winter residence. No stranger to cold, the tiny hummer migrates to breeding grounds as far as 61-degrees north latitude in Alaska. But it comes here for mild winters. Oops!

Birds stay warm in much the same way we do. We’re both endothermic, meaning warmblooded animals that generate internal body heat. Reptiles, such as lizards are ectothermic, meaning cold-blooded animals that generate body heat from warm environs.

Production of body heat in people and birds requires food converted into energy to maintain core body temperature. That’s why I braved outdoor temperatures as low as 6 degrees to fill the bird feeders with calorie-rich seed. I then returned to my frigid house to eat hot oatmeal.

Before nightfall, birds load their crops — a storage spot in their esophagus — with highcaloric seeds, berries and other foods. They slowly digest the food throughout the night, thereby generating energy to keep warm.

Feathers also shield birds from cold. Down feathers create a soft, fluffy inner layer that insulates the skin against loss of body heat. Contour feathers form an outer layer that seals out moisture and protects birds against cold air, freezing rain and snow.

The warmth from a bird’s feathers enables it to lower its nighttime body temperature, heart rate and respiration rate. It’s a process called torpor, which reduces metabolic rate to conserve energy on freezing nights.

The ability to withstand freezing temperatures allows nonmigratory songbirds, such as northern cardinals, to remain in Bangor during winter. Cardinals can get food by using their strong, conical beaks to crack open frozen nuts.

Migratory songbirds, including yellow-rumped warblers, come to Houston to pluck up ever-present insects and small seeds that are scarce during long winters in places like Bangor. Yet our rare weeklong freeze also made wild foods scarce.

Subfreezing weather doesn’t kill birds. What kills them is inadequate food and fresh water. I gave birds both, despite my frozen nose.

Photos by Kathy Adams Clark / Contributor Northern cardinals used bird feeders during the recent freeze to convert food into energy to maintain core body temperature.

This rufous hummingbird is no stranger to cold weather on its breeding grounds in Alaska but it migrates to Houston for mild winters.

Birds like this yellow-rumped warbler have learned ways to survive freezing weather.