Mammals of Jämtland / Jämtlands däggdjur / Norway Lemming / Fjällämmel

I'm dashing off a post in Starbucks while waiting to see if my pal Luke shows up (nb he didn't). I've been reading Kai Curry-Lindahl's book of animals in Sweden, The Animals in Colour / Djuren i färg (1955, 4th edn 1965). [Kai Curry-Lindahl (1917 - 1990), born in Stockholm, was a zoologist, conservationist, and for the last thirty years of his life an adviser to UN agencies based in Nairobi, with stints as a visiting professor to universities in the USA and Canada.]

As you'd expect many of the mammal species are limited to the southern half of Sweden, a similar situation as with plant species. Anyway to pass the time here's a list of the mammals that occur in Jämtland (a historic inland county, partly mountainous, in northern Sweden). (My "home" county, emotionally; it was where for many years my mum and dad had a summer cottage.) The distribution info is taken from the book, and is therefore a snapshot from the mid 20th century -- but I've given some updates in square brackets. 

Common Shrew (Vanlig näbbmus), Sorex araneus.

Eurasian Pygmy Shrew (Dvärgnäbbmus), Sorex minutus. 

Laxmann's Shrew (Lappnäbbmus), Sorex caecutiens (discovered in 1941) is in the far north, not Jämtland.

Eurasian Water Shrew (Vattennäbbmus), Neomys fodiens. 

Hedgehog (Igelkott), Erinaceus europaeus.   Jämtland is just outside its normal range, but it has been introduced in a few places. 

Whiskered Bat (Mustaschfladdermus), Myotis mystacinus. Common.

Daubenton's Bat (Vattenfladdermus), Myotis daubentonii. Reaches Jämtland, just. 

Brown Long-eared Bat (Långörad fladdermus), Plecotus auritus. Just reaches Härjedalen, the county just S. of Jämtland (and now in the same administrative county).

Northern Bat (Nordisk fladdermus), Eptesicus nilssonii. Common.

Mountain Hare (Skogshare), Lepus timidus. 

Red Squirrel (Ekorre), Sciurus vulgaris.

Beaver (Bäver), Castor fiber. The last native Swedish beaver was shot in Jämtland in 1871. In 1922 the species was reintroduced and quickly recolonized much of Sweden. A beaver dam at a nearby lake was one of the spots we visited annually. 

Northern Birch Mouse (Buskmus), Sicista betulina.

Black Rat (Svart råtta aka Takråtta), Rattus rattus. Now only fugitive in Sweden (ship escapes). Formerly common across much of the country in human habitats. 

Brown Rat (Brun råtta), Rattus norvegicus. Now in most towns and cities, except for some isolated ones e.g. in inland Lappland. (Despite the Latin name, it did not originate in Norway, but probably in C. Asia. The name arose from a belief, apparently false, that the rat came to Britain on ships from Norway; actually, it seems to have arrived in Britain before Norway.)

House Mouse (Husmus), Mus musculus. In human dwellings throughout Sweden.

Wood Mouse (Mindre skogsmus), Apodemus sylvaticus. Reaches Jämtland.

Yellow-necked Mouse (Större skogsmus aka Halsbandsmus), Apodemus flavicollis. Goes further north than Wood Mouse. In winter comes into houses and can be more numerous than House Mouse. 

Wood Lemming (Skogslämmel), Myopus schisticolor. A spruce forest species whose centre is southern Norrland. 

Norway Lemming (Fjällämmel), Lemmus lemmus. Across the whole Scandinavian fell region. [See below for a full translation of Curry-Lindahl's account.]

Bank Vole (Skogssork), Clethrionomys glareolus.

Northern Red-backed Vole (Rödsork), Clethrionomys rutilus, is a rare species of the far north. Not in Jämtland.

Grey Red-backed Vole (Gråsidig sork), Clethrionomys rufocanus. Characteristic Norrland species. 

European Water Vole (Vattensork), Arvicola terrestris.

Field Vole (Åkersork), Microtus agrestis. The commonest vole species in Sweden as a whole. There was a lot of vole activity in our cottage garden, but I don't know which species. 

Tundra Vole (Mellansork), Microtus oeconomus. A far northern species, but recorded in a few places further south, incl. some fell regions in Jämtland.

Muskrat (Bisamråtta), Ondatra zibethicus. N. American species illegally introduced in two places in Torneälven in the far north in 1944, and has spread, but not as far down as Jämtland at the time of the book.

Coypu (Sumpbäver), Myocastor coypus. S. American species recorded in various parts of Sweden; it may have reached Jämtland since this book. 

Wolf (Varg), Canis lupus. Sporadic in fell region as far south as Härjedalen. [It has probably spread quite a lot more since the book.]

Red Fox (Räv), Vulpes vulpes.

Arctic Fox (Fjällräv), Alopex lagopus [now renamed Vulpes lagopus]. As far down as Härjedalen in the fell region, but generally rare. [The species is outcompeted by the Red Fox except in "lemming years", which are now becoming less frequent, so Nils Christian Stenseth predicts its decline (according to the article linked below).]

Brown Bear (Björn or Brunbjörn), Ursus arctos. Throughout northern Sweden. [Has become more common since the book. Strömsund region in Jämtland is now thought to have the highest population of bears in Sweden.] 

European Pine Marten (Mård), Martes martes. Throughout Sweden but generally rare.

Stoat (Hermelin), Mustela erminea. 

Common Least Weasel (Småvessla), Mustela nivalis nivalis.   

Dwarf Weasel (Dvärgvessla), Mustela nivalis minuta . Recorded in various surrounding counties but not Jämtland at the time of the book.

Mink (Mink), Mustela vison. N. American species, introduced and now over much of Sweden.

Badger (Grävling), Meles meles. Its northern limit runs across Jämtland. 

Wolverine (Järv), Gulo gulo. Rare in fell regions.

Otter (Utter), Lutra lutra. 

Lynx (Lo), Lynx lynx. Once more widespread across Sweden, but Jämtland is one of the counties where it is still established.

Roe Deer (Rådjur), Capreolus capreolus. Spread widely through Norrland in recent years, including Jämtland.

Red Deer (Kronhjort), Cervus elaphus. Formerly more widespread, only established in Skåne in recent time, but scattered observations elsewhere, including Härjedalen in 1955.

Elk, Moose (Älg), Alces alces. Throughout Sweden. We'd come across them in the forest now and then.

Reindeer (Ren), Rangifer tarandus. There are no truly wild reindeer in Sweden any more (one of the last places was Härjedalen). Semi-domesticated free-roaming reindeer are common in the fells in summer, and in the woods in winter. 

Musk Ox (Myskoxe), Ovibos moschatus. Successful introduction in 1948 in Norway (Dovre) -- two earlier attempts in Sweden had failed. There were already reported sightings in the Swedish fells by 1955. [They are established in Härjedalen now (west of Tännäs).  Recently seen in Svenstavik in Jämtland.]

*

NORWAY LEMMING

There are many other accounts of this extraordinary species, but Curry-Lindahl's still seemed worth translating. I've broken it up into more paragraphs. I found his expression difficult and I've rehandled it quite a lot, but hopefully I haven't missed the point too often. 

NORWAY LEMMING [FJÄLLÄMMEL (=Fell Lemming)], Lemmus lemmus. 

A rustbrown, black and beige rodent with in an irascible temper in certain years; it may place itself in the fell-wanderer's path, hissing, simmering and trembling with rage if the animal finds retreat to its hole cut off.  

The Norway Lemming occurs along the whole Swedish mountain chain from Fulufjäll in Dalarna to the most northerly part of Lappland. Its appearances are very periodic. In some years the species can occur in extraordinary numbers in all mountain vegetation zones right down to the conifer forest, while in the intervening periods it can seem to have completely vanished. Up to and including 1942 Sweden's lemmings had a more or less pronounced 4-year cycle with regular and clearly noticeable frequency peaks roughly every fourth year, the so-called lemming years. The years 1945 and 1950 were partial lemming years, that is to say a certain increase in frequency (though no more so than other rodents) could be observed in the mountain regions of Härjedalen and Jämtland, while Lappland saw no peak after 1942 until 1960-61. 

The lemming's mass occurrences may briefly be explained thus: several successive years with conditions favourable for lemmings (climate, food), can lead to a sharp increase in the population, at an ever-increasing rate, and reproduction in some years occurs also in winter, probably right through the winter. It is this last-named circumstance that causes what seems a sudden mass occurrence, when the snow begins to melt in the spring. 

The mass migrations have been explained as caused by disease, psychosis, overpopulation or food scarcity. But what is certain is that the mountain heaths are able to supply enough food for the lemming population even at its peak, and the migrating lemmings have not been so disease-ridden as to prevent them establishing themselves and reproducing in new mountain locations. But it is a fact that many lemmings come to grief during the dispersals, which set off to every point of the compass: up to glaciers, down to lakes and rivers and woods, and sometimes, especially in Norway, even down to the sea. Many individuals resist being borne away and stay in their original location. However epidemics and pathological disturbances do occur and rapidly decimate the population, which besides is heavily preyed on by many animals. 

Lemmings inhabit all mountain zones, right up to the lichen zone, which is in fact its principal haunt and remains so in poor years as well as in good years. They have an impressive appetite and produce enormous quantities of excreta, which one sees traces of everywhere. They are most active at night. In winter they seek dry places in (especially) the willow and lichen zones, where they make extensive tunnel systems along the ground beneath the snow-cover, and where too they build round habitations out of grass, which are sometimes fastened to willow bushes where they remain hanging after the snow melts away. In summer the lemmings seek damper places among sedge, dwarf willows and dwarf birch. These seasonal movements, which must not be confused with the mass migrations, occur both horizontally and vertically depending on local circumstances. The species finds summer protection in the ground's natural hollows, or makes corridors beneath the shrub cover. The nests, which sometimes have two chambers (possibly remnants of the same female's different broods) can be situated here, there and everywhere; just as often in ground vegetation as in hollows under stones or the like. The lemmings' food consists of practically all the vegetable nourishment the mountains can offer: grass, seeds, moss, flowers, leaves, stems, bark, roots, etc. Exceptionally the species also consumes dead animals, and in captivity one lemming was seen to kill and eat a common lizard. 

-- The Norway Lemming produces several sounds: squeaking, hissing and screeching. Reproduction commonly begins in April-May, when the female in an early spring may already have her first litter, but in certain years reproduction also takes place through the winter, with several litters. Gestation is 18 days. The number of young in a litter varies between 2 and 11 (13 embryos have been witnessed); commonly there are 6-8, and in winter litters most often 2-4. The number of litters in a season has been estimated as 4-5 in a good year. When winter litters are produced the number per year becomes even higher, and the interval between birthings may be as low as 23 days. The young can see after 10-12 days. They are independent at 15-20 days and sexually mature at 20-35 days, varying in different years depending on environmental factors. The Norway Lemming can approach three years in age. It is also known as Fell Mouse (fjällmus) and Fell Rat* (fjällråtta). 

* But in spoken Swedish of this era, the word råttor was often used to mean mice, or rodents in general.

*

"Lemming years" were first described by Olaus Magnus in 1555. He explained them as lemmings falling from the sky, like a biblical plague. 

Chris Smith interviewing Nils Christian Stenseth:

https://sciencenorway.no/agriculture--fisheries-biology-ecology/falling-lemming-populations/1374950

According to this article, the regular cycle ceased in the 1990s, probably due to climate change. A crucial factor is cold dry snow in winter, which used to be reliable. This kind of snow creates the insulating protective cover that allows winter reproduction. Now that the winter snow is often wet, lemming population explosions have become less frequent and more irregular. (But as we've seen Curry-Lindahl already observed that the cycle was becoming less regular by the mid 1940s.)

This is useful too: 

https://animaldiversity.org/accounts/Lemmus_lemmus/

The change to winter snow structure is also a threat to reindeer in Finnmark, as described by Ben Rawlence here: https://www.theguardian.com/news/2022/jan/20/norway-arctic-circle-trees-sami-reindeer-global-heating . 

Until 2005, the average winter temperature in the region was -15C and it would reliably sink below -40C at least once during the winter, eliminating even the hardiest of all insect larvae, a process that kept the Arctic pest-free in the summer.

This world of winter was dark and cold and dry. At those temperatures there was no moisture at all. The snowpack was the consistency of sand, made up of several layers of large snow crystals. At -40C or-50C in the middle of winter, the quality and nature of snow crystals is critical to the survival of humans and animals alike.

When the temperature climbs back up towards zero or, even worse, above it, this delicate winter ecosystem collapses. Even a little warming of the snow can create havoc. Moisture starts to appear in the snowpack at -5C or -6C, at which point it loses its sand-like quality, and the snow starts to compact under the reindeer’s hooves, ruining the grazing beneath. If the thermometer goes all the way into the positive, as it has done increasingly in recent years, it is a catastrophe. Melting snow or rain will freeze when the temperature goes negative again, forming a crust of ice over the ground, locking the vegetation away from the browsing reindeer. This happened in 2013 and again in 2017. Tens of thousands of reindeer died; some herders lost more than a third of their animals.

Rodent droppings, from Spårboken (Danish text by Preben Bang, illustrations by Preben Dahlström, Swedish translation by Håkan Hallander, 1974).

Left (from top to bottom): Muskrat, European Water Vole, Norway Lemming, Field Vole.

Right (from top to bottom): Brown Rat, Black Rat, House Mouse, Wood Mouse.