White-footed Mouse
| Scientific Name | Peromyscus leucopus |
| Survival Strategy | Active All Winter |
| Conservation Status | Least Concern |
Spring
White-footed mice breed from March to October. The spring thaw reveals the tunnel system that protected these non-hibernating rodents from predators and extreme weather.
Summer
The female continues to produce pups throughout the summer.
Fall
After the last litter has been weaned and dispersed, mice will prepare for the hardships of winter by caching food and building a layer of brown fat.
Winter
White-footed mice are active all winter but remain in their nests during subzero temperatures. They rely on their food caches and brown fat deposits for survival.
Behavior
Reproduction
White-footed mice produce 2 to 4 litters per year, each with 2 to 9 offspring. Both males and females will breed with multiple mates (polygamous), so one litter often has newborns from different fathers. The pups are born naked and blind (altricial) after a gestation period of 22 to 28 days and open their eyes after two weeks. At about three weeks, the young mice are weaned and independent of their mother. Juvenile white-footed mice reach sexual maturity at about 44 days.
Huddling
To conserve life-sustaining energy on cold days, white-footed mice will huddle together in groups of two to six in nests insulated with whatever soft, fluffy material they can find. The insulation often consists of plant material but could also be from the upholstery of a winterized camper or a collection of feathers from a chicken coop. An abandoned woodpecker hole or hollow branch are typical locations for mice nests, but they are just as likely to build their nest under the hood of a diesel tractor.
Living in the Subnivean Zone
White-footed mice are one of several species to take advantage of the subnivean zone.
The subnivean zone is the narrow boundary between the top of the soil and the bottom of the snow layer. If the snow is deep enough to provide insulation, the temperature in the subnivean zone will remain just a few degrees below freezing, even if the air above is well below zero. The mice will build a network of tunnels that allow them to forage for food while protected from the bitter cold and most predators. White-footed mice will occasionally cache food in the subnivean zone, but this can be a risky gamble because a January thaw could expose their precious food supply, leaving them less able to survive the bitter weather still to come.
Physiology
Daily Torpor
Torpor is an energy-conserving adaptation where an animal reduces the need to burn calories by slowing all non-essential activities to a bare minimum. White-footed mice enter a state of daily torpor when the air temperature falls below 3˚C (37˚F), at which time they will lower their body temperature by about 17 degrees and slow their metabolism by 75%. These nocturnal rodents typically enter torpor at sunrise and are active by late afternoon.
Extra Hemoglobin
As fall weather becomes colder, white-footed mice produce new red blood cells with higher hemoglobin content. Hemoglobin is the protein in blood that transports oxygen into and carbon dioxide out of every cell. With more oxygen, mice can increase their metabolic rates and their ability to keep warm. This hemoglobin performance boost is the same process that got US bikers in trouble for “blood doping” at the 1984 Olympic Games in Los Angeles.
Brown Fat Provides Fuel
Like other mammals, white-footed mice build a layer of brown fat (brown adipose tissue) in response to colder weather in mid-September. In winter, they can generate heat by releasing the energy stored in this brown fat through metabolism. Brown fat has more mitochondria than white fat, and these mitochondria act like fat-burning stoves which produce heat quickly. This layer of fat also serves as extra insulation. The winter diet of the white-footed mouse would not provide enough nutrition to survive a harsh winter in the upper Midwest without the energy stored in brown fat.
Diet
White-footed mice are omnivores, and their diet consists of seasonally available seeds, berries, acorns, insects, stored grains, and fungi. As non-hibernators, white-footed mice must cache food for the winter. Anyone who has discovered a pile of sunflower seeds in an old boot has experienced one of these food caches.
Lifespan and Mortality
Most white-footed mice live for one year or less. As with many species, the first months of life are the most lethal.
Predators
White-footed mice are prey for any carnivore large enough to swallow them. The list of predators includes weasels, snakes, owls, hawks, kestrels, merlins, sandhill cranes, and red foxes.
Climate Vulnerability
The range of the white-footed mouse will likely expand northward in a warmer climate. Because white-footed mice are primary carriers of the bacteria that causes Lyme disease, this tick-transmitted infection will likely increase its range as well.
Never Stop Learning
Cryptic Behavior: The white-footed mouse will create a buzzing sound by drumming on a dry leaf with its front paws. Biologists do not know for sure why it makes this sound.
References
| Aguilar, S. 2011. “Peromyscus leucopus” (On-line), Animal Diversity Web. Accessed January 19, 2022 at https://animaldiversity.org/accounts/Peromyscus_leucopus/ |
| Roy-Dufresne E, Logan T, Simon JA, Chmura GL, Millien V (2013) Poleward Expansion of the White-Footed Mouse (Peromyscus leucopus) under Climate Change: Implications for the Spread of Lyme Disease. PLOS ONE 8(11): e80724. https://doi.org/10.1371/journal.pone.0080724 |
| Seasonal Study of Spontaneous Daily Torpor in the White-Footed Mouse, Peromyscus leucopus G. Robert Lynch, F. Daniel Vogt, and Harvey R. Smith, Physiological Zoology 1978 51:3, 289-299 https://doi.org/10.1086/physzool.51.3.30155746 |
| Hiker’s Notebook: White-footed Mouse https://hikersnotebook.blog/fauna/mammals/white-footed-mouse/ |
| Heinrich, Bernd. Winter World: The Ingenuity of Animal Survival. Harper Perennial, 2009. |