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What do animals do in the fall?
The autumn skies might be full of migrating birds, but much of Britain’s wildlife will be slowing down after a hot and hectic summer. But despite the shortening days, a handful of species are clocking in some serious overtime.
First up, meet the mammals that embrace the romance - and drama - of the season.
Red deer are the largest land mammals in the UK and are possibly best known for their breeding behaviour which occurs from the end of September to November. Known as the rut, it is a hormone-charged time as males compete for dominance and mating access to hinds (females). Stags roar, walk in parallel and shove one another with their outsized antlers. The powerful blows dealt can result in injury and death while success in battle requires further exertion to mate with harems numbering as many as 20 females.
The deer are early risers - much of the activity takes place around dawn - but fights can persist throughout the day and after dark. Even when exhausted, the males must keep their wits about them as subordinates can sneakily mount hinds that are left unattended.
It’s not just males that are busy, researchers have found that some female fallow deer mate with multiple bucks throughout their rutting season. Scientists from Queen Mary University, London, theorise that this polyandry works as a type of insurance for females. If the dominant buck is older or has a large harem his sperm may be depleted, so females could improve their chances of becoming pregnant by mating more than once in a season.
Meanwhile, female grey seals are braving stormy seas to bring new life into the world. After a summer gorging on rich fish stocks, the pregnant pinnipeds travel to northern and western rocky shorelines to give birth to their young. The weather here might be wild, but the mothers are in great shape to suckle their young – feeding them on rich milk to supercharge their development. Yet after only 2-3 weeks, the pups are abruptly weaned and left to their fates by mothers who are ready to mate again.
Bull seals come to shore in anticipation of the females entering oestrus (their fertile period) but can become a nuisance to the fresh, still fluffy pups. Similarly to the deer, male seals fight for dominance in aggressive tussles - so pups must contend with adults making love and war.
It’s not just mammals with reproductive urges in autumn, it’s spawning time for fish species such as sea trout and Atlantic salmon. Both species start to return from the sea and swim upstream to their birthplaces during the summer. Early arrivals will wait in deep pools until it is time to breed, while late comers must battle the additional obstacles thrown up by autumn flood waters. Salmon are famous for leaping up weirs and waterfalls to get to their spawning sites and provide quite a seasonal spectacle. In October and November, females lay their eggs in “redds” scraped on the gravelly river bed and males fertilise them. Sea trout and salmon rarely feed in freshwater so they must rely on their reserves for the return journey back to the sea.
Many insect species have already left their legacy in egg form to spring into life next year, and the adults expire as temperatures drop. Daddy long legs, or crane flies, hold out longer and are common sights in September when they seek out places to leave their offspring. But the adults will mostly be swept away by heavier rains in October.
Red green carpet moths, peacock and small tortoiseshell butterflies are on the wing as they seek out suitable shelter – sometimes in houses. They are among the few moth and butterfly species that ‘overwinter’ by entering a state of torpor to survive until the warm days of spring. They can be roused early by central heating, in which case they’re best left in a cool sheltered spot to return to their rest.
The most familiar insect house-hunters in autumn are ladybirds, especially when they settle around window frames by the dozen. While they are usually solitary, the beetles become more sociable and respond positively to the touch of fellow ladybirds in autumn. They will huddle up in large aggregations which increase their chances of surviving the winter. While various native species will be sheltering in leaf litter, harlequins (invasive ‘newcomers’ to the British Isles from Asia) are less cold-tolerant and attracted to light-coloured surfaces around human homes, thought to mimic the natural rock formations in their native lands. Once they find somewhere suitable for overwintering, they lay down chemical clues to invite more ladybirds to the same site.
In addition to sex and shelter, food is the other key motivating factor behind the rush of autumn activity. Grey squirrels, which spend more time foraging on the ground than their red cousins, will bury thousands of the season’s abundance of nuts to provide a larder through winter. Their caches are scattered throughout woodlands, and scientists have found the animals have excellent spatial memories that help them retrieve their stores. With an estimated 25% of their caches vulnerable to theft by other squirrels and birds, the smart mammals employ sophisticated problem solving skills to protect their snacks. In a balancing act to ensure they don’t expend too much energy, they decide when to eat a nut, store it – or try to conceal their behaviour from onlookers.
Jays exhibit similar sneaky behaviour. These forest relatives of crows can bury as many as 5000 acorns in autumn but prefer to do so by bushes or trees where their activity can be screened from observers. The famously screechy birds, whose scientific name means “babbler of the acorns”, also make the effort to cache in quieter locations and will vocalize less when there’s a chance to pilfer from another.
Next time you take a relaxing walk through fallen leaves, perhaps spare a thought for the industrious species that have to step it up this season.
Featured image by Mark Bridger | Getty