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 leave a trail of mucus in their wake. Before the waters recede, each limpet retraces its route, following chemical cues in the mucus, back to its home scar. The mucus also increases the amount of algae that settles and grows, so in effect the limpets are ‘farming’ their food. There’s much more to the humble limpet than meets the eye.
Oyster Beds
How do shoreline creatures ever sleep? And do oysters and other such shellfish dream? Tedbun
This is a deceptively simple question that’s actually fiendishly difficult to answer. That’s because sleep is something of a biological enigma and biologists grapple even to agree on a definition of what constitutes sleep or why it’s necessary. If you think about it, it makes no sense for an animal to stop paying attention to the world around it when there are so many potential dangers. So there must be a really good biological reason for it beyond simply resting – we just haven’t worked out what that is yet!
All animals go through periods of activity and inactivity, even those that live on a shoreline and are bashed about by waves. Physiologically, sleeping