The snowy owl's biology is closely tied to the availability of lemmings.
These herbivorous rodents are largish members of the vole clan that are the predominant mammal of the tundra ecosystem alongside the reindeer and probably make up the majority of the mammalian biomass of the ecosystem.
Lemmings are key architects of the soil, microtopography and plant life of the entire tundra.
In the American lower Arctic areas, brown lemming of the Lemmus genus are predominant and tend to be found found in lower, wetter habitats (feeding by preference on grasses sedges and mosses) while collared lemmings of the Dicrostonyx genus were in more arid, often higher elevation habitats with heathland and ate by preference willow leaves and forbs.
The southerly brown lemmings behave differently than more northern collared lemming type, increasing almost limitlessly within preferred habitat whereas the collared type tends to spread to suboptimal habitats and therefore does not appear reach the high regional densities of the brown.
Authorities now generally agree that there appears to be no synchrony between the brown and collared lemmings and the feeding access of snowy owls is irregular as a result, but snowy owls can likely alternate between the two lemming types as one or the other increases as they nomadically use different parts of the Arctic.
It is possible that the rare coincidental mutual peak of both lemming types within a year results in the erratic high productivity that results in irruptions.
Within individual Arctic lemming species, historically, populations can vary in rough 4- to 5-year trends.
As a result, in areas such as Banks Island, the breeding rate of snowy owls can vary within a decade by about tenfold.
Weights of lemmings taken can range from 30 to 95 g (1.1 to 3.4 oz) on Baffin Island, while those taken in Barrow averaged 70.3 and 77.8 g (2.48 and 2.74 oz) in female and male lemming, respectively.
It was estimated based on captive daily food intake that a snowy owl may consume about 326 g (11.5 oz) of lemmings a day, though other estimates using voles show a daily need for about 145 to 150 g (5.1 to 5.3 oz).
On Southampton Island, 97% of the diet was lemmings.
A very similar number of lemmings (nearly 100%) were found over 25 years of study in Barrow, amongst 42,177 cumulative prey items.
Of 76 lemmings that could be identified to sex at a cache, male lemmings were found in the cache twice as often as female lemmings.
While initial findings indicated on Wrangel Island that female lemmings outnumbered males in prey remains, to the contrary osteology indicated that, like Barrow, males were more often taken.
However, the slightly larger, slower-moving females may be preferred when available.

In some areas, snowy owls can breed where lemmings are uncommon to essentially absent.
Even in Barrow, where the diet is quite homogenously based in lemmings, the hatching of passerines, shorebirds and waterfowl can provide a key resource when lemmings are not found regularly and may be the only means by which the young can survive at such lean times.
In the Nome, Alaska area, the locally nesting snowy owls reportedly switched from lemmings to ptarmigans when the latter's chicks hatched.
A somewhat varying diet was also reported in Prince of Wales Island, Nunavut where 78.3% of the biomass was lemmings, with 17.8% from waterfowl, 3.3% from weasel and about 1% from other birds.
In Fennoscandia, among 2,700 prey items only a third were Norway lemmings (Lemmus lemmus) and a majority were voles at 50.6%, probably largely the tundra vole (Microtus oeconomus).
A more detailed glance at Finnish Lapland showed that amongst 2,062 prey items, 32.5% of the foods were Norway lemmings (though in some years the balance could range up to 58.1%), 28% were grey red-backed voles (Myodes rufocanus) and 12.6% were tundra voles, with birds constituting a very small amount of the prey balance (1.1%).
In northern Sweden, a more homogenous diet was found with the Norway lemming constituting about 90% of the foods.
In the Yamal Peninsula, 40% of the diet
The snowy owl's biology is closely tied to the availability of lemmings. These herbivorous rodents are largish members of the vole clan that are the predominant mammal of the tundra ecosystem alongside the reindeer and probably make up the majority of the mammalian biomass of the ecosystem. Lemmings are key architects of the soil, microtopography and plant life of the entire tundra. In the American lower Arctic areas, brown lemming of the Lemmus genus are predominant and tend to be found found in lower, wetter habitats (feeding by preference on grasses sedges and mosses) while collared lemmings of the Dicrostonyx genus were in more arid, often higher elevation habitats with heathland and ate by preference willow leaves and forbs. The southerly brown lemmings behave differently than more northern collared lemming type, increasing almost limitlessly within preferred habitat whereas the collared type tends to spread to suboptimal habitats and therefore does not appear reach the high regional densities of the brown. Authorities now generally agree that there appears to be no synchrony between the brown and collared lemmings and the feeding access of snowy owls is irregular as a result, but snowy owls can likely alternate between the two lemming types as one or the other increases as they nomadically use different parts of the Arctic. It is possible that the rare coincidental mutual peak of both lemming types within a year results in the erratic high productivity that results in irruptions. Within individual Arctic lemming species, historically, populations can vary in rough 4- to 5-year trends. As a result, in areas such as Banks Island, the breeding rate of snowy owls can vary within a decade by about tenfold. Weights of lemmings taken can range from 30 to 95 g (1.1 to 3.4 oz) on Baffin Island, while those taken in Barrow averaged 70.3 and 77.8 g (2.48 and 2.74 oz) in female and male lemming, respectively. It was estimated based on captive daily food intake that a snowy owl may consume about 326 g (11.5 oz) of lemmings a day, though other estimates using voles show a daily need for about 145 to 150 g (5.1 to 5.3 oz). On Southampton Island, 97% of the diet was lemmings. A very similar number of lemmings (nearly 100%) were found over 25 years of study in Barrow, amongst 42,177 cumulative prey items. Of 76 lemmings that could be identified to sex at a cache, male lemmings were found in the cache twice as often as female lemmings. While initial findings indicated on Wrangel Island that female lemmings outnumbered males in prey remains, to the contrary osteology indicated that, like Barrow, males were more often taken. However, the slightly larger, slower-moving females may be preferred when available.
In some areas, snowy owls can breed where lemmings are uncommon to essentially absent. Even in Barrow, where the diet is quite homogenously based in lemmings, the hatching of passerines, shorebirds and waterfowl can provide a key resource when lemmings are not found regularly and may be the only means by which the young can survive at such lean times. In the Nome, Alaska area, the locally nesting snowy owls reportedly switched from lemmings to ptarmigans when the latter's chicks hatched. A somewhat varying diet was also reported in Prince of Wales Island, Nunavut where 78.3% of the biomass was lemmings, with 17.8% from waterfowl, 3.3% from weasel and about 1% from other birds. In Fennoscandia, among 2,700 prey items only a third were Norway lemmings (Lemmus lemmus) and a majority were voles at 50.6%, probably largely the tundra vole (Microtus oeconomus). A more detailed glance at Finnish Lapland showed that amongst 2,062 prey items, 32.5% of the foods were Norway lemmings (though in some years the balance could range up to 58.1%), 28% were grey red-backed voles (Myodes rufocanus) and 12.6% were tundra voles, with birds constituting a very small amount of the prey balance (1.1%). In northern Sweden, a more homogenous diet was found with the Norway lemming constituting about 90% of the foods. In the Yamal Peninsula, 40% of the diet 
Snowy owl