The American Robin (Turdus migratorius) is a common and familiar backyard bird found throughout most of North America. Many robins migrate south for the winter, but a significant number overwinter in their breeding ranges, even in northern states and Canada. Robins are able to survive cold winters due to a variety of behavioral and physiological adaptations.
Quick Answers:
– Robins primarily survive winter by switching to a berry-heavy diet and forming large communal roosts for warmth.
– They conserve energy by lowering their body temperature and becoming inactive for long periods.
– Robins grow extra feathers for insulation and may grow specialized leg feathers for warmth.
– On very cold nights, robins burrow into dense vegetation or fluff up their feathers to trap body heat.
What Do Robins Eat in Winter?
Robins switch their diet in the winter to focus on fruits that persist through the cold months. They rely heavily on foods like berries and crabapples, supplementing with any insects or other invertebrates they can find. Some key winter foods include:
Berries
– Juniper berries
– Holly berries
– Sumac berries
– Pyracantha berries
– Mistletoe berries
– Rose hips
– Crabapple fruits
Other Fruits
– Persimmons
– Mountain ash fruits
– Toyon fruits
– Virginia creeper fruits
Invertebrates
– Beetles
– Butterfly pupae
– Moth cocoons
– Spider eggs
– Centipedes
– Earthworms
– Grubs hiding under bark
Robins will flock to fruiting trees and shrubs, sometimes traveling miles to reach a food source. They often return to the same winter foraging sites year after year. The birds voraciously consume fruits, often devouring the entire crop of a tree or shrub over the span of a few days.
In late winter, robins also feed on the early buds of elm, maple, and other trees. Flower nectar provides an important source of sugar. Robins generally avoid bird feeders in winter but may visit platforms stocked with raisins or mealworms.
How Do Robins Conserve Energy in Winter?
To reduce energy expenditure during cold weather, robins adopt a number of behavioral and physiological adaptations:
Lowered Body Temperature
Robins lower their core body temperature by 2-5°C during winter nights. This reduces their metabolic rate and energy needs.
Inactivity
Robins spend up to 75% of winter days hunkered down in sheltered spots. Remaining inactive conserves calories.
Fluffed Feathers
Fluffing up feathers creates insulation and helps robins retain body heat.
Communal Roosting
By roosting together in dense vegetation, robins share body heat. This can raise the temperature inside a roost by up to 20°C.
Burrowing in Leaf Litter
On very cold nights, robins burrow into the ground or under leaf litter. This shelters them from wind and retains heat.
Sunning
Robins sun themselves on open branches to raise their body temperature.
Shivering
If necessary, robins shiver their flight muscles to generate heat. But this requires extra energy expenditure.
How Do Robins Stay Insulated in Winter?
To retain body heat, robins grow specialized plumage in winter:
Extra Feathers
– Robins grow more contour feathers for insulation. Their winter coat can have up to 35% more feathers than during summer.
Downy Feathers
– An increase in downy feathers under the contour feathers boosts insulation. Down feathers trap air to retain heat.
Leg Feathers
– Some robins even grow feathers all the way down their legs and feet. This likely helps minimize heat loss through their exposed skin.
Fluffed Plumage
– Roosting robins fluff out all their feathers, trapping air pockets for insulation. They may also tuck their bills under their feathers.
Heat Exchange
– Arteries and veins run close together in robins’ legs so that blood flow to the extremities exchanges heat with blood returning from the feet. This helps minimize heat loss.
How Do Robins Survive Frigid Winter Nights?
Robins use a variety of strategies to make it through bitterly cold winter nights:
Communal Roosting
– Robins gather in large communal roosts of 100s or 1000s of birds. This allows them to share body heat.
Sheltered Roost Sites
– Favored roosting sites include thick conifers, holly trees, orchards, or vine-tangled woodlands. These offer insulation and wind protection.
Heat Retention
– Fluffing feathers, tucking bills into plumage, burrowing into soil or under leaves all help retain heat through the night.
Snow Shelters
– In areas with deep snow, robins burrow tunnels into the snow to create shelter from wind and cold.
Food Fuel
– Robins may gorge on berries in late afternoon to build fat reserves that provide energy through the night.
Dropping Temperature
– By lowering their core temperature 2-5°C, robins reduce energy consumption and can get by with less fuel.
How does winter weather affect robin survival?
Severe winter weather can threaten robins despite their adaptations. Extended periods of extreme cold and storms impact robin survival in the following ways:
Freezing
Prolonged temperatures below -20°C can freeze robins, especially their feet and bill. This can lead to frostbite injuries or even death.
Starvation
Ice storms can coat fruit and prevent robins from accessing food. Intense cold limits robin foraging time. Lack of food leads to starvation.
Exposure
Strong winds or disrupted shelter makes it harder for robins to stay insulated. Prolonged exposure can be fatal.
Mobility Impacts
Deep snow piles can prevent robins from reaching food sources or escaping predators. Icy roads make it difficult to find traction.
Calorie Depletion
Trying to survive sustained sub-zero temperatures burns more calories. Robins may run out of energy reserves.
Stress
Harsh conditions force robins into emergency survival mode for extended periods. This chronic stress threatens their health.
What strategies help robins get through winter storms?
When faced with severe winter weather, robins turn to additional behaviors and survival strategies:
Emergency Foraging
– Robins broaden their diet and forage more widely, even visiting bird feeders stocked with fruit.
Snow Shelters
– Burrowing into snowdrifts offers insulation during storms.
Wind Blocks
– Roosting behind windbreaks like treelines reduces exposure.
Heat Sources
– Robins congregate near warm microclimates like springs or rooftop heat vents.
Feather Puffed Maximum
– Fluffing feathers to the max insulates against wind chill and retains heat.
Rotating Perches
– Shifting positions in communal roosts ensures all birds get turns at the warmer center.
Snow Melting
– Robins seek out surfaces like roads and sidewalks warmed enough to melt snow for access to food and grit.
Lowered Body Temperature
– Dropping their body temperature further reduces energy consumption during storms.
How do robins survive migration and winter on northern coasts?
Along the Pacific, Atlantic, and Gulf coasts, many robins overwinter rather than migrating further south. These coastal populations rely on the following to survive:
Coastal Microclimates
– Coastal areas tend to be warmer than inland regions in winter. Temperature extremes are buffered near oceans.
Aquatic Food Sources
– Beaches and tidal flats offer marine invertebrates like mollusks and crustaceans as winter foods.
Fruits Persist Later
– Fruits on trees and vines in coastal areas stay edible longer into winter due to milder temperatures.
Wind Protection
– Dunes, bluffs, and beach vegetation provide windbreaks for roosting and shelter.
Ocean Effects
– The thermal mass of nearby oceans keeps coastal areas warmer through greenhouse effects.
Microclimates
– Cavities in cliff faces, tall beach grasses, and brushy dunes create warmer microclimates for roosts.
Milder Winters
– Coastal regions tend to get less snow, ice, and fewer Arctic fronts relative to inland areas.
Do robins need to store food to survive winter?
Unlike some birds, robins do not create food caches to survive winter. There are a few reasons robins get by without storing up food:
Varied, Seasonal Diet
– Robins are adaptable generalists, not food specialists. They can switch between insect and fruit diets.
Communal Roosts
– Flocks share information on the location of each day’s best food sources.
Mobility
– Robins can cover large territories to take advantage of ephemeral food bonanzas like crabapple gluts.
Expanding Home Ranges
– Some robins that breed in the far north migrate south to more moderate wintering grounds with better foraging.
Milder Urban Areas
– Urban robins may overwinter farther north due to heat island effects and backyard food sources.
Fat Reserves
– Robins build up fat deposits to help survive short-term food scarcity during storms.
Opportunistic Foraging
– Robins will eat at bird feeders, visit springs, and seek out microclimates in winter to find food daily.
How do juvenile robins survive their first winter?
Juvenile robins face extra challenges surviving their first winter, including:
Lack of Experience
– Young robins must learn essential skills like foraging techniques, predator avoidance, and finding natural food sources and roosts.
Poor Quality Molt
– Juveniles often grow inferior insulating feathers compared to adults. Their winter coat is less protective.
Competition
– Adult robins often chase young birds away from the safest food bonanzas and prime roosting spots.
Poorer Condition
– Months of stress from the fledgling period may leave juveniles in poorer condition to withstand winter.
Lower Status
– Subordinate juvenile birds get less time warming up in the centers of roosts.
Limited Energy Reserves
– Without several seasons to hone their foraging skills, young robins may start winter with fewer fat reserves.
Naivety
– Unfamiliarity with winter hazards like road traffic and predators imperils younger birds.
Due to these disadvantages, juvenile robin mortality over the winter may be significantly higher than adult mortality. Those that do survive their first winter develop valuable experience.
How do urban robins fare better in winter than rural ones?
Studies show that robins wintering in urban and suburban areas have higher overwinter survival rates than rural robins. This is attributed to several urban advantages:
Warm Microclimates
Cities tend to be warmer than natural habitats in winter due to heat island effects. This reduces robin energy expenditure.
Access to Food
Backyard bird feeders, ornamental fruiting trees and shrubs, and reliable anthropogenic food sources help sustain urban robins.
Shelter
Buildings, bridges, and other structures offer sheltered roosting spots. Underground steam pipes and vents provide warmth.
Reduced Competition
Lower densities of overwintering birds in cities means reduced competition for limited food and shelter.
Fewer Predators
Urban predator populations like raptors and coyotes are also lower, meaning safer conditions for robins.
Milder Climate
The built environment mitigates severe low temperatures, icy roads, deep snow, and other deadly rural conditions.
Human Help
Some people provide emergency food or shelter on bitterly cold nights when robins are in crisis.
Thanks to these advantages, urban robins are almost twice as likely to survive winter compared to rural ones.
Conclusion
American robins have evolved a diverse array of behavioral and physiological strategies that allow them to make it through harsh northern winters. Their adaptability to variably cold conditions is impressive. However, severe winters still pose a major threat. The magnitude of juvenile mortality indicates just how challenging winter can be. Milder urban areas provide safer overwintering habitat for robins. But even city birds struggle to get by during storms and cold snaps. The availability of winter food sources and shelter sites is a key factor influencing whether robins can successfully survive until spring in northern climates.