Adaptive temperature regulation in the little bird in winter: predictions from a stochastic dynamic programming model

Research output: Contribution to journalArticle


Several species of small birds are resident in boreal forests where environmental temperatures can be −20 to −30 °C, or even lower, in winter. As winter days are short, and food is scarce, winter survival is a challenge for small endothermic animals. A bird of this size will have to gain almost 10% of its lean body mass in fat every day to sustain overnight metabolism. Birds such as parids (titmice and chickadees) can use facultative hypothermia, a process in which body temperature is actively down-regulated to a specific level, to reduce heat loss and thus save energy. During cold winter nights, these birds may decrease body temperature from the normal from 42 ° down to 35 °C, or even lower in some species. However, birds are unable to move in this deep hypothermic state, making it a risky strategy if predators are around. Why, then, do small northern birds enter a potentially dangerous physiological state for a relatively small reduction in energy expenditure? We used stochastic dynamic programming to investigate this. Our model suggests that the use of nocturnal hypothermia at night is paramount in these biomes, as it would increase winter survival for a small northern bird by 58% over a winter of 100 days. Our model also explains the phenomenon known as winter fattening, and its relationship to thermoregulation, in northern birds.


External organisations
  • UiT The Arctic University of Norway, Tromsø
Research areas and keywords

Subject classification (UKÄ) – MANDATORY

  • Ecology


  • Body temperature regulation, Dynamic programming, Facultative hypothermia, Heterothermy, Hypothermia, Little bird in winter, Winter fattening
Original languageEnglish
Pages (from-to)43-54
Issue number1
Early online date2017 Aug 3
Publication statusPublished - 2017 Sep
Publication categoryResearch