Acrobatic blue and Great Tits
Well, the colorful agile little
blue and great tits which frequent our gardens in winter area a delight to
watch as they cluster round a bag of peanuts. Blue and great tits, both
colloquially known as tomtits, are popular garden birds which visit bird tables
regularly in winter. Both are widespread throughout the British Isles and you
will see them in deciduous woodland, scrubland, hedgerows and farmland
everywhere. The blue tit is an agile, aggressive, always excitedly active
little bird which specializes in hanging at awkward angles to feed, while the
great tit, larger than the blue and twice as heavy often prefers to feed on the
ground like a finch. Male and female blue tits are very similar in appearance.
Among great tits a distinguishing features between male and female is the black
line which runs down the Centre of their primrose yellow breasts. This is faint
in the female but very bold and wide in the male.
Seasonal foraging;
Well, in summer blue tits feed
mainly on insects searching for them at the tips of twigs and shoots. In winter
this diet is supplemented with occasional nuts and seeds. Since insects are
neither active nor easily visible in winter, blue tits have to spend
considerable time peering and probing round buds and under flakes of bark to
find hibernating adults and larvae. If you observe the apparently aimless you
will see that it is in fact purposefully searching every potentially rewarding
nook and cranny. In the garden the boldness and agility of blue tits as they
attack peanuts hung in a plastic mesh sock is a delight to watch. They feed on
almost everything put out on a bird table except bird seed, but above all they
prefer nuts and fat. Great tits eat much the same food as the blue, but take
more vegetable food in winter particularly seeds and nuts which have fallen to
the ground.
Feeding for breeding
The breeding season for great
tits begins in late March and for blue tits in early April. To get into peak
condition for egg laying as early as possible earlier broods tend to the larger
and healthier than later ones the female must eat prodigiously. In the three
weeks before laying begins, she puts on weight at an extraordinary rate,
increasing her normal weight by at least a half and sometimes more. Then over
10 or 12 days she produces almost her own weight in eggs, laying one each day.
This remarkable feat cannot be achieved by the female unaided. The male must
feed her. The behavior called courtship feeding may be essential if breeding is
to be successful. The female tit does
all the best building, choosing a hole or crevice in a wall, tree or garden nest
box. The nest a cup of moss, grass, wool, leaves, roots and spiders webs is
lined with hair or feature.
All Eggs in one Basket
In summer in deciduous woodland,
both great and blue tits often rely heavily on just one species of insect as
food for themselves and their young. In oak woods this is the winter moth which
frequently produces huge numbers of caterpillars. The parent birds need to
synchronize the maximum food demands of their young with the single, short
lived peak in the caterpillar food supply. They therefore produce a single
large brood each year. This is unlike most other small birds which rear two or
even three broods a year and thus have two or three chances if anything goes
wrong. It is almost literally a case of the tits putting all their eggs in one
basket!
One in Ten Survive
In spring each breeding pair of
tits is generally composed of one adult bird which bred the year before and is at
least 21 months old, and one young bird which is about nine months old and
breeding for the first time. One half of each breeding pair dies each year. For
the population to remain steady, only one youngster would need to be reared per
pair to replace the dead adult. On average, however, ten youngsters leave each
nest in summer. This means that nine die by the following spring a staggering
90% mortality rate. Gruesome though it sounds, this is an insurance against
catastrophe and is quite usual in the bird world. Indeed, if one extra
youngster per brood were to survive each year, the whole countryside would soon
be overrun by hordes of tits eating up all available resources and
precipitating a disastrous drop in the population.
Plenty of Predators
The high mortality rate is
largely the result of natural causes, especially starvation, since
inexperienced young birds have difficulty finding enough food in winter.
Moreover also at the start of the season, competition for nesting holes is
fierce. Larger birds such as the starling may oust tits from the bigger holes,
and tit may oust tit from smaller ones. The larger great tit does not always
succeed in evicting the smaller but more aggressive blue. Tree sparrows can
squeeze through an entrance apparently only just large enough for a blue tit,
and often build their untidy nest on top of a clutch of tit eggs or as tree
sparrows are late nesters, even on top of a flourishing brood of chicks.
Predators also play a significant
part in the high mortality rate, and may account for a third or more of the
deaths. Great spotted woodpeckers have a taste for tit eggs and young and can
easily open up a nest hole with their strong beak. Woodpeckers capitalize on
the fact that well grown tit chicks are alerted by a shadow falling across
their nest hole and jump up to the entrance to grab the expected food from a
returning parent. As soon as the unfortunate chicks appear, the woodpecker catches
them. In the early days after fledging the inexperienced youngsters may fall
easy victims to hunting sparrow hawks.
Strangely enough wood mice and
sometimes voles climb trees readily and enjoy any eggs they happen to find. The
prime predatory mammal however, is the weasel which can squeeze through the
nest hole without much difficulty. Often the weasel will gorge on young birds
to such an extent that it has to sleep off the meal until it slims down enough
to squeeze out again. Weasel predation is particularly high in summers when the
weather is poor and the young tits are underfed. The hungry chicks squeak
noisily for more food and are heard by patrolling weasels on the lookout for
prey.
Irruptions
The general trend in tit numbers
is more or less steady, but there are some fluctuations from year to year.
Often, after a series of good summers and mild winters especially on the
continent), mortality is lower than usual and consequently tit numbers far
higher than average. In this situation, the sudden onset of a severe winter, or
a shortage of natural food, produces a massive westward movement called an
irruption as hungry birds move about in search of food. When these hordes cross
the channel, autumn numbers in the eastern counties of England reach
spectacular levels. Strange reports sometimes appear of tits eating the putty
round window frames and even entering houses and tearing strips of wallpaper
off the walls. Irruptions occur irregularly, perhaps only once a decade.
Ringing results show the at most
of the birds in irruption are of continental origin, coming from as far away as
eastern Poland. Winters in mainland Europe are generally more severer than in
much of Bri9tain and Ireland, so Continental blue and great tits migrate south
and west in autumn to escape climatic hardship and to find easier feeding
.British birds, on the other hand, tend to stay close to home, and although
they may roam around several parishes, rarely make journeys of more than 30 miles.
Many establish a circuit of known good feeding spots and visit each in turn.
Mixed Flocking
Anyone walking in deciduous woods
between August and March is likely to encounter a tit flock. These roving bands
of birds operate from ground level to the top of the tree canopy, probing for
food and flying from perch to perch. In late summer young willow warblers and
chiffchaffs, fattening up before migration, may join the tits. Later gold
crests, nuthatches and chaffinches also turn up, as well as wrens and tree
creepers. Wrens tend to search the ground for food, while tree creepers probe
the tree trunk for concealed insects. The small coal and blue tits favor the
ends of twigs high in the canopy, as do the even smaller, warblers which hover
in front of the twigs, picking off insects. Lower on branches and trunk, you
will see great tits and nuthatches whose greater weight excludes them from the
canopy. Great tits often feed with chaffinches on the woodland floor, picking
up seeds and nuts. One advantage of mixed flocking is that a large group of
birds has many eyes to watch for predators and give the alarm quickly. Another
is that the trees are exploited for food on every level.
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