Sunday, 10 March 2013

And the year began...with something a foot.

January / February 2013

  The early days of the year had few redeeming features. The rainfall theme of 2012 look set to continue until the temperatures finally dipped, and the snow arrived by the blizzard. The more hardier Sanctuary residents, such as the chimpanzees, ventured out into their freshly whitened surroundings (prompting international fame for Nakima), but most were content to remain indoors, watching the cold from their heated quarters. Only Julie, the snow monkey (Japanese macaque), was in her natural environment, yet she too was attracted to the indoor warmth, like her species is drawn to the natural hot-springs of Nagano, Japan.
  By the end of January, the recent snow had largely melted but the air remained cold. Frequent showers of rain and hail drove hard from a slate grey sky. Trodden grass was mulched into mud. Rivers were high and raucous. Wildlife was sparse, preferring to shelter from the elements, only surfacing to quench their most essential needs. The treecreeper was one such venturer, scouring the tree trunks for spiders and insects, its curved, slender bill breaching the natural cracks and crevices in the bark.

Treecreeper (Certhia familiaris)


  As I watched, I was drawn to the small bird's motion, spiralling up the tree with the natural ease of our horizontal stroll. Even the wings, casually folded back into its streamlined body, seemed to emphasise the ease with which it engaged this vertical ascent, mimicking - almost mocking - the way our hands clasp behind our backs as we embark on a leisurely constitutional.
  When admiring birds, I suppose it is the wings to which we are usually drawn. After all, they are the biological motors of our envy, wonder, and much sought action: flight. They are largely the reason for the birds success on this planet, providing them with a pocket of co-existence just above our heads. But it is also on the wing that the bird looks more comfortable, providing a grace, stealth and agility it often lacks on the ground. In comparison, the feet often appear weak and spindly, as they awkwardly transport the bird a hop or two at a time. They offer no recourse for escape, just a cumbersome bipod for when they are most vulnerable.
  Yet the feet of this remarkable treecreeper reveals a different story, as they speedily propel this bird up the tree. And so I look closer. In common with most UK songbirds, the treecreepers' feet are anisodactyl. This means there are four digits, with three toes facing front and the fourth facing back. Each toe has a curved keratin claw, which the treecreeper uses to grip onto the wood and moss. In the above photographs, it can also be seen using its tail as a prop. 

  Another proficient climber is the nuthatch. Seen here gripping onto a telephone pole with similarly long, hooked claws, it can often be seen scurrying up and down the sanctuary's surrounding trees. Verticality holds no fear for this bird, as its grip on wood is sufficiently strong to descend at quite a speed. It will also make use of the sunflower seeds offered from the bird tables of surrounding gardens, particularly in winter, when invertebrate can be harder to find.

Nuthatch (Sitta europaea)

  The size of foot and claw vary from species to species, as demonstrated by this female house sparrow, whose feet appear much smaller than those of the treecreeper and nuthatch. Despite also being anisodactyl, three toes forward one back, their feet are better suited for perching. 

Female house sparrow (Passer domesticus)

  Male house sparrow (Passer domesticus)

Coal tit (Periparus ater)

  The toes of the anisodactyl foot can move independently of each other. Such flexibility maximises the ability to grip onto different objects and surfaces, something which is essential for their access to food and cover from predators. When perching, the back toe comes round to meet the forward facing three. Although they do not possess the dexterity of the human hand, the action is reminiscent of opposable thumbs, and the grip a gymnast uses to secure a hold on the parallel bars.

Great tit (Parus major)


Song thrush (Turdus philomelos)


  As a bird sits, an ankle tendon automatically locks the anisodactyl toes into position around the perch. This allows them to feel secure, particularly when sleeping at height. When the bird stands, the tendon unlocks the toes, releasing the bird to move freely on or from its chosen perch.

Female house sparrow (Passer domesticus)

   This blue tit perfectly demonstrates the feet's strength of grip, and the flexibility it affords the small bird. But it also shows its delicacy of touch.

Blue tit (Cyanistes caeruleus)

  Appreciating the fragility of dead leaves, the bird is clearly applying a measured amount of pressure, ensuring it does not pierce or destroy its chosen perch.

 Jackdaw (Corvus mendula)


  Perching birds are typically known as "passerines" as they, together with over 5,000 species, are included in the scientific classification order, "Passeriformes". Observing a perching bird, it can appear that much of its flexibility comes from a knee that bends forward in the opposite direction to that of the human joint. But where we might expect the knee to be in relation to our bodies, is actually the passerines' ankle. The knee is further up the leg, largely unseen, hidden by feathers.  

  Those independent digits are also useful to secure food in position when eating. In this instance the food appears to be bread, but the action becomes that much more relevant when a bird needs to tear flesh with its bill.

  The flesh tearing action is a particular feature of birds of prey, whose feet have evolved into talons. This evolutionary trait has allowed them to specialise in hunting for small mammals and birds. During the winter, the common buzzard remains a regular sight at the sanctuary, scouring the surrounding countryside with its keen eye.

Common buzzard (Buteo buteo)


  Like the buzzard, the grey heron likes to fulfil its carnivorous side, and are often seen fishing along the Sanctuary's nearby rivers, which are well stocked with fish.

likely id: Rainbow trout (Oncorhynchus mykiss) taken September 2012

  Unlike the raptors, the heron does not use its feet to inflict a killing blow, but will use them to entice prey by creating vibrations in the water. This is known as Foot Stirring, and is covered at www.heronconservation in a paper called "The terminology of courtship, nesting, feeding and maintenance in herons" by James A Kushlan.
  The heron will wait patiently in the river shallows, using its bill to spear passing fish that it will then swallow whole. The herons' anisodactyl toes are slender and long, and unlike most birds, whose feet fold in when flying, the herons' feet trail behind them in flight, perhaps creating a drag that is more than made up by an impressive wingspan.

Grey Heron (Ardea cinerea)

 Another fish-eater on the local rivers is the goosander. Its webbed feet, the unseen motor, manoeuvres the bird along the water in search of prey. When discovered, it submerges its head to snatch the unsuspecting fish with its razor bill. The photos below show how the bright orange feet help propel the goosander from the water to the air.

Male goosander (Mergus merganser)

Female goosander (Mergus merganser)

  As ever, the mallard ducks continue their life on the freshwater surrounding Baboon Island, but the lone moorhen appears to have found a mate. It is nice to consider the prospect of further moorhens at the sanctuary this spring.
  Every year, there is a fight to survive the challenges winter brings. There is a prevalence of the more common birds, whose higher population makes them better prepared to take the mortality strain compared to those of lesser numbers. There are plenty of robins, tits, chaffinches, sparrows, blackbirds, and corvids, as well as a healthy spattering of wrens and dunnocks. But it is always nice to see a bird that can be a little more difficult to spot, even in summer, such as the bullfinch.

Male bullfinch (Pyrrhula pyrrhula)


  With spring threatening, the wildlife is preparing for the start of a new cycle. Their attention is turning to nesting, mates, and a new generation. Daffodils and early crocus have joined the flowering gorse bushes in colouring the landscape. They are a hopeful sign against the whim of nature. 

Early crocus (Crocus tommasinianus)

Male and female blackbird (Turdus merula)


No comments:

Post a Comment