Birds and predators
1 WHY DO BIRDS ‘MOB’ MUCH LARGER PREDATORS?
Smaller birds will harass predators, such as owls, to drive them away from an area. Sometimes they work alone, but often their calls attract other birds. It’s thought they do this to make themselves a nuisance, and to signal to the predator that they have been spotted. However, there is also evidence that the smaller birds hope to alert an even bigger bird of prey to scare the predator away.
2 HOW DO THEY GET OTHER SPECIES TO HELP?
A predator is clearly perceived as a risk to all the smaller birds nearby, and a small mixed flock of different species will often work together to create a hostile environment. Species within the tit family have a common language to call for aid: a two-part call consisting of a general warning call of high, piercing notes to say ‘there’s a predator here’, followed by a series of buzzing notes that mean ‘come and help me’.
Blue tits have a warning call. Below: tawny owls are often mobbed.
3 IS IT RISKY FOR THEM?
Occasionally birds of prey turn their weapons on the smaller birds, harassing them, but, surprisingly, this rarely happens. Normally, predatory birds either ignore the commotion going on around them, or calmly move on to a quieter location. Most birds of prey and owls are not adapted to hunt on alert, agile birds in flight. They would have no chance of catching any of the smaller birds buzzing around them – and it appears that the mobbing birds are well aware of this. Kate Risely
Like
their cephalopod cousins, the cuttlefish and octopuses, squid have skin packed with pigment-filled cells called chromatophores. These receive instructions from nerves to expand and contract thereby revealing and hiding their colour, rapidly adjusting the skin’s appearance. The resulting kaleidoscopic trickery is useful for camouflage, but squid may also use particular patterns to communicate.
Recently, scientists pored over film of packs of human-sized Humboldt squid hunting in the deep, dark waters of the twilight zone. They identified more than a dozen repeated
‘phrases’ – such as dark stripes along a squid’s arms or dark eyes combined with a pale body.
These seemed to help coordinate the hunt and stopped squid from bumping into each other as they chased lanternfish.
The squids’ skin is also bioluminescent, so their messages glow in the dark. The phrases have yet to be translated, but one could mean ‘Oi! That fish is mine!’.
LOOPER CATERPILLAR
It’s a dangerous time of year for caterpillars. A single nestful of blue tit chicks will happily get through 1,000 in a day. But this particular caterpillar is less likely to be spotted than most. It’s a member of the geometrid moth family, which has a song – Inchworm – written about it. The larvae have a characteristic gait and legs only at their front and rear ends – perfect for mimicking twigs, and many geometrids do just that. But with its disguise completed with faux bark textures and lichen encrustations, this inchworm has gone the extra mile.