I have got a number of questions asking how birds cope in winter in
Tromsø, in the cold and without the benefit of sufficient daylight. I think
I can find no clearer answer than by repeating myself and again sending a
piece first sent ti Birdchat 27 decmber 1997----how time flies!! I reckon
there must be an almost complete turnover of subscribers since then, and
the others can just delete this.
Wim Vader,
Tromsø Museum
9037 Tromsø,
Norway
WINTERING BIRDS AT 70*N; HOW DO THEY COPE?
After my last mailings several people have asked me: how come there are
any birds at all in Tromsoe in winter, and how do they cope? I have
therfore decided to reply "in plenum", although much will be well-known
stuff to most of you.
The birds that stay here in Tromsoe, N.Norway (69'50`N) in winter are
not
a random mix: insect eaters have little to search for here, and ground
feeders are also at a severe disadvantage, as the ground is normally
covered by a quite thick snow cover (today is exceptional, we had a
damaging western storm, and incredibly mild temperatures for December, up
to +10*C!)).Also, all freshwater is frozen over and covered with snow.
Cold as such is usually not a problem, quite apart from the
fact that
because of the proximity of the sea (We live on an island) it does not get
really cold in Tromsoe: minimum temperatures in town are ca -15*C, cold by
Brisbane standards but not by Norwegian standards--inthe inland here temp.
may fall to -50*C! As long as the birds have sufficiently to eat, they also
usually will mange the cold pretty good.
Here is little daylight now, just 2 hours or so of twilight.
Just now it
looks even darker, as a very strong outbreak of Atlantic air (Severe
westerly storm and temp up to +10*C!) has melted most of the snow, and made
everything much gloomier-looking. Still, many birds mange quite well, and
the following gives an idea of how they do this.
The winter birds here fall into different categories:
1) Sea birds. This is the largest group. The sea and most of the fjords do
never freeze over, and most seabirds, especially those not dependent upon
sight only, can live comfortably here in winter. Also some birds that
frequent fresh water in summer, winter on the shore; good examples are the
mallards Anas platyrhynchos and the Grey Heron Ardea cinerea (pretty much a
coastal bird up here also in summer, though). Also a few Dippers Cinclus
cinclus vcan be found on the shore, but most of the ones that winter here
(Some fly to Finland) stay at rapids and similar places where there is open
water even in midwinter.
The most comon seabirds in winter here are sea ducks (Northern
Eider
Somateria mollissima, King Eider S. spectabilis, Oldsquaw Clangula
hyemalis, Common Scoter Melanitta nigra and Red-breasted Merganser Mergus
serrator. Of these the mergansers eat fish, while the others are benthic
feeders and apparently well able to find their food also in the dark of our
winter days. Auks Alcidae are not common in the fjords here, unless there
is an influx of small pelagic fish; then murres Uria aalge and U. lomvia
and razorbills Alca torda flocks may be seen. Dovekies Alle alle do occur,
but they are much more common further south. Cormorants Phalacrocorax carbo
are much more common around the town than they are in summer; a few
shipwrecks are litterally festooned with them.
2) Gulls and crows: The flocks of ducks are attended by large gulls, mostly
Larus argentatus and L. marinus, who harrass the submerging ducks
mercilessly and steal a lot of their food. Often one can watch gulls
defending "their duck flock" against interlopers. These gulls, together
with smaller numbers of Glaucous gulls L. hyperboreus, also scavengealong
the quays in town and on the garbage dump, together with Raven Corvus corax
and Hooded Crows C.corone cornix. And the crows, together with Black-billed
Magpie (The most conspicuous land bird in the area in winter) scavenge
around in town, i.a. there where the towns people feed our feral pigeons.
3) Shore birds: These are almost absent in winter. Even though the sea does
not freeze, there is often a lot of ice in the intertidal and many small
fish and invertebrates retreat to somewhat deeper water in winter.
Shorebirds are therefore quite rare, with a single exception. the Purple
Sandpiper Calidris maritima, a plump, short-legged bird well adapted to the
cold, is common on stony Troms shores in winter, when it mainly feeds on
littorinid snails. As told before, also Grey herons winter here, a
phenomenon of recent years.
4) Tree-feeding birds: Numbers vary a lot from year to year, changing with
the vicissitudes of the crops of their major food-plants. Rowanberries
Sorbus aucuparia have bumper crops every few years, and then thrushes
Turdus pilaris and T. iliacus remain up north for at least part of the
winter, until the berries are finished. During such years we can have
influxes (invasions is too grand a word here) of Bohemian Waxwings
Bombycilla garrulus and Pine Grosbeaks Pinicola enucleator. The last two
years the rowans have had very meagre crops, and then the thrushes
disappear in October, and the other species go elsewhere.
The crop of birch seeds has a lot to say for the number of Redpolls
Acanthis flammea and A. hornemanni, and rich crops of pine or
(introduced)spruce cones can give lingering and even nesting crossbills
Loxia pityopsittacus and l. curvirostra
Another category of wintering birds are the insectivores that change
their menu and feed largely as vegetarians during the dark period. Here
belong the tits Parus major and Parus montanus,and the woodpeckers Picoides
spp. Woodpeckers feed on pine cone seeds in winter, and also Great and
Willow tits shift to seeds to a large degree. I have the strong impression
that the Great Tit is more or less dependent on human assistance (i.e.
feeding with sunfloers seeds and other seeds) in this area, while the
Willow Tit has another trick on its sleeve: it caches many small loads of
seeds and insects in the autumn, that it uncovers and feeds on in the
winter time (Tree creepers Certhia familiaris often rob these caches and so
profit also)
5) Bulk food vegetarians: These are mainly the grouse: Willow grouse and
Ptarmifan Lagopus lagopus and L. mutus feed mostly on willow buds and
twigs, Balck Grouse Tetrao tetrix om birch, and Capercaillie T. urogallus
on pine needles.These are all bulk foods, that are easy to find even in the
dark, and that stick up out of the snow. Bullfinches Purrhula pyrrhula
also feed on buds, but also these wonderful birds have discovered the
advantages of using human feeders.
6) Insectivores: Amazingly enough the smallest bird of all, the Goldcrest
Regulus regulus, is mainly insectivorous also in winter. This often is its
undoung; especially when the trees get covered by a layer of ice, mortality
is large. Numbers of Goldcrests therefore oscillate wildly from year to year.
7) Commensals of man: Crows and magpies , as well as many gulls, and when
the fish mael factories are working, even the eiders, come in here, and as
said, I am tempted to put also the great tit in this bag. In addition the
House Sparrows Passer domesticus is I think dependent on winter feeding,
eother directly or by scavenging on the feeding of the pigeons, and our few
pairs of Collared turtles Streptopelia decaocto would never survive the
winter here without people taking special care of then in their gardens.
8) Predators. Clearly there are enough birds left in winter to feed a
number of predators. The city birds are at risk from Sparrow Hawk and
Goshawk Accipiter nisus and A. gentilis, and I`ve seen Gyrfalcons Falco
rusticolus catching feral pigeons, although their usual prey is the grouse.
the White-tailed Eagle Haliaeetus albicilla is a scavenger as well as a
predator, but it does catch quite a number of ducks and gulls. Owls we have
few here near the coast, where snow cover usually is thicker than in the
inland.
Several of you have expressed amazement that we have any landbirds at
all
during winter. This is why!
God Jul and Godt Nyttaar to all of you!
Wim Vader, Tromsoe Museum
9037 Tromsoe, Norway
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