Guide

Look closerBirds

How ducks and geese stand on ice without freezing their feet

January to March

Mallards, Canada geese and gulls can stand on pond ice or snow without their bare feet freezing. Warm blood heading down the leg hands its heat to cold blood coming back up, so the feet stay cold, close to freezing but not below it, and lose very little body heat.

Why this time of year

Mallards gather on parks and ponds in large numbers in fall and winter, and Canada geese are here all year, so a pond with ice or snow at its edge is a good place to look for birds standing on it. Ducks Unlimited Canada reports that in mallards, just five percent of their total body heat escapes through their feet.

How to notice it

  1. From the shore of a park pond, look for ducks, geese or gulls standing on ice, on snow, or in shallow icy water.
  2. Find a bird standing on one leg with the other foot tucked up into its belly feathers, and watch whether it switches legs after a while.
  3. Look for birds that have sat down flat on the ice or snow, which covers their feet with warm feathers.
  4. Notice how calm they look: their feet are kept cold, and a cold foot loses less heat to the ice than a warm one would.

Try this with kids: From the shore, count how many birds are standing on one leg. Wait a minute and see if any of them switch legs.

Phrase to know: “Countercurrent heat exchange”: the blood vessels going down to the feet run right beside the ones coming back, so heat passes across to the returning blood instead of leaking out through the feet.

Safety

  • Watch from the shore. Never step onto pond ice for a closer look, and keep dogs off it too.

Sources

  • massaudubon.orgPrimary (Mass Audubon, dated January 1, 2021). Names waterfowl AND gulls and the mechanism, the one-foot stance, and ice: 'Waterfowl, gulls, and other large-footed waterbirds take things a step further with a special "countercurrent" circulatory system.' 'The veins and arteries in their legs run right next to each other so the warm blood from their heart heats the cold blood returning from the feet. This keeps them just warm enough so they don't freeze when standing on ice.' Also: 'You'll often see birds in winter standing on one foot, tucking the other into their bodies, then alternating when the standing foot needs a respite.' And legs are 'made mostly of tendon with very little muscle or blood flow, which reduces heat loss.' Permanent article, not a rolling page.
  • audubon.orgPrimary (National Audubon, Audubon magazine, Andrew Del-Colle, published January 26, 2026; lead image is a Mallard). 'the system, called a countercurrent heat exchange, works so well that ducks and other waterfowl can stand on ice for hours without ever having to worry about injury.' The detailed explanation is in a graphic that was not machine-readable; only the text sentences are relied on.
  • iwwr.ducks.caSecondary/expert (Ducks Unlimited Canada, Institute for Wetland and Waterfowl Research; quotes David Howerter, PhD; no publication date shown). Mechanism: 'This process occurs in the leg, where arterial blood is cooled by venous blood, which in turn warms up a few degrees.' Cold-on-purpose angle: 'By lowering the temperature of blood flowing through its foot, ducks are able to conserve heat' and 'the smaller the temperature difference between two objects (in this case, ice and feet) the more slowly heat is exchanged.' The only number used, species-attributed: 'in the case of mallards just five per cent of their total body heat escapes through their feet.' One-leg tuck: 'If a bird is especially cold, it may lift one foot and tuck it into its feathers to help conserve heat.'
  • niehs.nih.govPrimary/government (NIH NIEHS Kids Pages, a lightly playful 'Human Bird' framing but the science text is straight). Feet near but above freezing: 'the feet stay a rather constant temperature, above freezing. When walking on ice or swimming in icy waters, the feet approach freezing but never reach it.' Sitting and one leg: 'Both humans and some birds also practice sitting on their feet to keep them warm. Standing on one leg or sitting on the ground may help warm the feet.' Mechanism: 'Warm arterial blood flowing down to the feet passes close to cold venous blood returning from the feet.' Limit: 'Frostbite can occur during very harsh winters, or when there is a sudden temperature drop.' No species-specific foot temperature is given; the page's 41oC figure is core body temperature, not the foot.
  • massaudubon.orgPrimary (Mass Audubon). Winter presence on ponds in Massachusetts: 'Mallards can be seen in parks and ponds in large numbers in fall and winter but will break off into pairs when breeding season comes.'
  • massaudubon.orgPrimary (Mass Audubon State of the Birds). Canada geese present year-round in Massachusetts: 'Increasing populations of year-round resident Canada Geese are enjoying the benefits of grassy playing fields and park food handouts.' Wintering habitat listed includes 'Rivers, Lakes, and Ponds' and 'Urban and Suburban'.
  • primacklab.blogspot.comAcademic blog (Richard Primack lab, Boston University), used only for the March end of the window. Eastern Massachusetts pond ice often lasts into March: 'from 1995 to 2014 ice-out at Walden Pond has varied from as early as January 29 in the record-breaking warm winter of 2012 to as late as April 5 in 2005'. Shows ice is weather-dependent, which is why the card is CONDITIONALLY_LIKELY and its text also covers snow and icy water.
  • archive.journeynorth.orgSecondary dataset (Journey North archive, dates 'collected by Journey North students', no longer updated). Year-by-year ice-out dates 1995-2014 for an eastern Massachusetts pond; most years fall in March (e.g. 2007 March 28, 2009 March 23, 2011 March 30), with 2012 January 29 the outlier. Supports including month 3.

Checked against these sources on November 6, 2026.

In the guide for January, February, March

Also worth noticing