Springwatch Unsprung: Why Do Robins Have Red Breasts?. Jo Stevens

Чтение книги онлайн.

СКАЧАТЬ

      What happens to fledglings during their first few nights in the big world? Do the parents stay close by or do they call throughout the night as reassurance to the young? Or, apart from feeding, are the young basically alone? Tony from Gloucester

      When fledglings leave the nest, am I right in assuming they never return to it? In which case, where do they spend their first night outdoors? I know that the nests get quite dirty and parasite-ridden, but even so it seems awfully harsh that they spend all their young lives in the safety of a warm nest and then – BAM! – just like that they’re out on their own, never to return? Kate

      How ‘capable’ should blue tits be when they fledge? I have a blue tit nest in the vent of an extractor fan and the three young left the nest two days ago. They were feathery but barely able to toddle, let alone fly, and showed no inclination at all to seek shelter or move away from a potential predator – me. Five hours later, when almost fully dark, two were still sitting out in the open on my doorstep cheeping loudly. I haven’t seen them since, dead or alive, but they didn’t look like survivors. Did they jump too soon, or are blue tit babies always like this? Stocksfield

      Leaving the nest is one of the most dangerous times in a bird’s life. Fledglings need to learn fast; they have to work out how to fly, find their own food and avoid becoming someone else’s dinner. Mortality is high and many blue tit chicks don’t make it – only 38 per cent live for over a year. This is why blue tits lay so many eggs in a clutch (usually 8–10 but up to 16), to increase the chances of at least some of them living to adulthood.

      Once chicks of garden birds leave the nest, they rarely return. As Kate points out, the nest is pretty smelly after having a growing family squeezed into it for a while, with droppings and food remains building up. That scent can attract predators. Instead, it is safer for chicks to leave the nest and venture out into the big wide world.

      Many garden birds fledge just before they can fly and blackbird chicks leave the nest two or three days before they can take to the air. Fledglings often split up and hide in inconspicuous places, waiting to be fed by their parents. From the parents’ point of view, it’s safer to split up their offspring around a garden than risk keeping them together where, if found, all the chicks may be taken. Blue tit parents encourage their chicks to leave the nest by enticing them with food and calling to them. Those blue tits chirping on the doorstep were certainly in a risky position, as usually parents would guide their youngsters to a safe place.

      If you do find an apparently abandoned chick, don’t be tempted to ‘save’ it too hastily. Instead, try leaving it alone and watch from a distance unless it is in immediate danger or very exposed, in which case move it quickly and gently into some cover, like a bush. The parents are probably nearby and will return to look after it when the coast is clear. Fledgling blue tits usually stay with their parents for a couple of weeks, relying on them for food initially while they learn how to be a blue tit and fend for themselves.

      Angry Birds

      Why do blue tits fly up to windows and try to ‘attack’ their reflections? Cal

      During the breeding season, birds are fired up by hormones and males can become particularly feisty, especially if they are trying to defend a territory. If the resident male catches sight of his reflection in a window, car wing mirror or other shiny surface he will try to see off the apparent ‘intruder’. It is most common to see this behaviour in spring, but birds that hold territories throughout the year, such as robins and grey wagtails, may be up for a fight at almost any time. A robin wouldn’t hang around attacking a mirror for long, though, as it defends its patch by finding a higher perch than its rival and would soon lose its reflection. An angry bird can be very persistent, keeping up the aggression for hours or sometimes days – this intruder just won’t leave! Usually the bird won’t hurt itself but it is a huge waste of their time and energy. If you’re concerned (or irritated!) you can help to remove the reflection by covering the window or mirror with paper or fabric.

      You may be wondering why the bird doesn’t recognise its own reflection like we would. Natural reflections are rare and would soon disappear if attacked, for example in a puddle or pond. Very few animal species have been shown to recognise their own reflection, but biologists are very interested in this ability because it can give an insight into how animals’ minds work. To find out if an animal can recognise itself in a mirror, biologists put a coloured mark somewhere on its body while it’s unconscious or asleep in a place that it would only be able to see in a mirror, for example under its chin or on the end of its nose. If the animal pays attention to the mark in its reflection and touches its skin then this suggests that the animal understands that the reflection is itself. The ability to recognise oneself in a mirror suggests some kind of self-awareness.

      A human baby doesn’t work out that the infant it can see in the mirror is actually itself until it reaches about 18 months old. This is about the same time that children develop what’s called a ‘theory of mind’; that is, they can infer what other people are thinking or feeling and begin to be able to put themselves in someone else’s shoes. Whether animals can do the same is a matter of huge debate among biologists who study animal behaviour. So far the only other animals shown to recognise their own reflections are similarly large-brained mammals such as chimpanzees, orangutans, elephants and bottlenose dolphins. However, there is one bird that has passed the mirror test: the magpie. Members of the crow family have been shown to be very intelligent, but does this mean that they are self-aware too …? It’s certainly food for thought.

      No Place Like Home

      Limpets – do they return to exactly the same place each time the tide goes out? I’ve noticed the ones stuck to irregular surfaces have the fringe of their shell shaped to fit the surface (like a jigsaw puzzle), so they must return to the same spot and shuffle around to exactly the same orientation too. Who’d have thought that? Incredible! Or am I wrong? Steve, Edinburgh

      Steve is absolutely right. Limpets are true homebodies, returning to exactly the same spot on the rocky shore at each tide. As they settle into position, their shells grind against the rock and, over time, they form an indentation called a scar. The limpet’s shell fits snugly against this scar and forms a tight seal that prevents the limpets drying out when the tide goes out. Like many animals that live on the shore, they have to tolerate the cycle of being exposed and inundated by seawater twice a day. They also have to endure strong wave action, drying out (limpets can survive up to 65 per cent water loss) and alternating extremes of temperature – from baking in the summer sun (well, sometimes!) to freezing cold seawater. Limpets are tough!

      They’re also renowned for their ability to cling onto the rock using their powerful, muscular foot for suction and ‘glue’ for adhesion. This not only helps them to retain water but also deters predators such as birds. That’s not their only defence, though; limpets use moves that a wrestler would be proud of! They can ‘mushroom’, lifting their shell upwards then bringing it down suddenly, stomping on any starfish or other marine predator that comes too close.

      At only six centimetres across and three centimetres high it’s easy to underestimate these apparently simple creatures, but limpets are architects of their environment. Their grazing keeps algal growth in check, removing young seaweeds. They have a special rasping organ called a radula with sharp ‘teeth’ set in 160 rows, each containing 12 teeth. Their tips are hardened with iron and silica. Limpets move across the rocks, grazing on a thin film of algae or small larvae. You may be able to see the scraping marks, pale zigzag lines, left behind on the rocks. As they slowly wander across the rocks they СКАЧАТЬ