Cuckoos are brood parasites and rely on parents of the host species to bring up their chicks. Female cuckoos wait for a suitable nest to be left unattended before flying down, removing one of the host’s eggs and replacing it with one of her own. She can lay the egg and make a quick getaway in about 10 seconds. When the unsuspecting parents return they incubate the cuckoo egg and raise the chick as their own. The cuckoo chick usually hatches first and ejects all the other eggs or chicks from the nest, ensuring it has no rivals for its surrogate parents’ attention. Meanwhile the cuckoo parents return to Africa and never see their chicks. Instead, the host parents work tirelessly to feed the enormous chick, which can grow to over three times their own size. When the cuckoo finally fledges, it must find its own way to Africa. In the cuckoo’s case, the ability to migrate must be genetically hard-wired in the brain and is innate rather than learned.
But how does a cuckoo avoid sexual imprinting on the wrong species and know that it is a cuckoo rather than a reed warbler or a dunnock? Biologists aren’t entirely sure how cuckoos learn to recognise a mate and there may be several processes at work. Perhaps some innate elements are later reinforced by mixing with other cuckoos. Brown-headed cowbirds, which use the same breeding strategy as cuckoos, have been shown to use a species-specific ‘password’ to trigger their learning. They make a particular chatter call when they join up after fledging and then learn more about their species. They also look to themselves and reference their own traits, such as ‘that bird looks like me so probably belongs to the same species’. Cuckoos are likely to have a similar system for working out their own identity and recognising which birds are potential mates.
Awkward Embrace
We noticed one of our smallish koi carp desperately flipping and trying to free itself from what looked like a black ‘growth’ around its head and gills. We netted the fish and discovered a large toad had it tightly in its grasp. My husband forced the toad off the exhausted fish, which has now recovered in a bucket. The toad jumped back into the pond where there are more fish! We’ve never seen this before. Was the toad trying to ‘mate’ with the fish? Jill, Sussex
In essence, yes, the koi carp was on the receiving end of an overexcited toad’s amorous attentions! As soon as night-time temperatures reach 5 degrees Celsius or more, usually in February, adult common toads emerge from hibernation. They have just one thing on their mind: mating. They migrate back to their ancestral pond, often travelling several kilometres and crossing dangerous, busy roads. The males often arrive before the females and will lie in wait, either at the pond itself or nearby, ready to pounce on a potential mate. The smaller male will often piggyback on the larger female as she makes her way to the water.
The male grasps tightly onto the female under the armpits in a special hold called amplexus, Latin for ‘embrace’. During the breeding season the male develops ‘nuptial pads’ on his first three fingers that help him grip onto the female. Males are so intent on breeding that they will often grab toads of the wrong sex or even completely different species like the unfortunate koi carp. Males usually outnumber females at the breeding ponds and competition for mates is high, so it makes sense to grab anything that moves and ask questions later! Actually, males aren’t even that choosy, and have been known to latch on to inanimate objects while in their aroused state.
Male toads will croak their objections loudly if grabbed by mistake, and usually the grabber will let go within a few seconds. Fish can’t be so vocal, though, and there would have been no audible cue to encourage the confused toad to release Jill’s fish. It was lucky that Jill’s husband spotted the embrace when he did, otherwise the koi carp may have endured a long struggle. Male toads are persistent and will often hang on to the female for several days. One female may attract the attentions of several males, resulting in a writhing orgy of warty skin and interlocked limbs – who’d be a female toad?! Eventually the strongest male will be successful and will fertilise the female’s eggs as she lays them, up to 6,000 eggs in long double strings.
One study found that 80 per cent of males returned to the pond where they were spawned, so it’s likely that Jill’s toad was a tadpole in her pond, perhaps before it was stocked with fish. Toads can be long-lived and lucky individuals may reach up to 40 years old, so it might be worth keeping an eye out for this overzealous toad for a few years to come.
Confusing Courtship
The males and females of some birds, such as robins, look identical. So how does a male robin know he is chatting up a female robin, and not another fella? And why do they both have red breasts? Sue
Many birds are sexually dimorphic – that is, the male and female look very different. Usually, the males are the more colourful, showy sex and females tend to be more drab. Perhaps the most extreme example of this is the peacock, with its magnificent blue-green tail that creates a dazzling fan. However, familiar British birds such as grouse, blackbirds and many species of duck, such as mallards, also have males that are more eye-catching than the females. Other birds have more subtle cues, such as the yellower chests of male blue tits that are particularly apparent when viewed in ultraviolet light, which birds, unlike humans, can detect.
In 1859 Charles Darwin first proposed that male birds used elaborate plumage to impress females in his book On the Origin of Species. He argued that the males evolved ornaments such as beautiful feathers, or beguiling courtship rituals like the complex dances performed by birds of paradise, to woo the females, which then choose their partners according to their fitness. At the time, Darwin’s entire theory of evolution was controversial and met with much consternation, but the concept of female choice was especially scandalous at a time when women had little control over their lives in a patriarchal Victorian society.
Anyway, back to robins! Robins are unusual because both males and females hold territories throughout the year and defend them vigorously. Their red chest feathers act as a warning to other robins rather than an attraction to potential mates. The male and female both have bright orange/red breasts that stand out amid the gloom of dusk and dawn when they are often active. They use their beautiful song and brilliant red chests to see off any intruders. A robin will find a high perch, fluff out the feathers to show as much red as possible then sing out its melodious war song. If the vivid red chest is their war paint, then their song is their battle cry.
Most of the time, the opponent submits and a fight is avoided. If not, the owner will attack, and may even peck the other bird to death. Up to 10 per cent of robins might die in this way. Robins are so feisty that any object of a similar colour may be attacked, like the apocryphal red rag to a bull. We’ve had reports of assaults on orange lawnmowers, red socks and even someone gardening in a red jumper.
From late December onwards, the robin’s thoughts turn to romance, but courtship can be confusing when both sexes look almost the same. The male may be a little brighter and slightly larger than the female but even robins may have difficulty telling the sexes apart. They have to take into account how a robin acts rather than rely on how it looks. During the breeding season, females approach their chosen male’s territory with care. Sometimes, the male mistakes his lover for a fighter and initially responds aggressively, singing at the ‘intruder’. She patiently listens and doesn’t sing back – instead she follows him around. After a few hours, her patience pays off and he finally accepts her. They set up home together and both fiercely defend their patch. Robins may look cute and appealing but they are gutsy little warriors.
Topsy Turvy
How do bats hang upside for so long without any adverse effects, such as poor blood circulation? The Chameleon
Bats spend the daylight hours hanging upside down in a secluded spot, such as the roof of a cave or the inside