Seasonal Update (October 2021)

As autumn picks up pace, the reduced daylength and cooler temperatures cause trees to cut their losses and drop their leaves. As the leaves die the green chlorophyll pigment breaks down to reveal a range of reds, yellows, oranges and purples hitherto hidden from view. - Credit: Marc Baldwin

Welcome to mid-autumn. Things are starting to feel a bit more seasonal after a very warm September. During the second week we saw temperatures reach 30C (86F) in the east Midlands, and most of the month remained well into the 20s Celsius (low 70s Fahrenheit) over much of the UK and Republic of Ireland. More widely we also saw some striking heat in the Northern Hemisphere, with Jahra in Kuwait taking the unenviable record with 50.1C (122F) on 1st September. In the Southern Hemisphere, the record went to Corumba in Brazil, which reached 43.9C (111F) on 20th September. Europe suffered a mix of flooding and wildfires, even volcanoes, with Spain particularly badly hit.

Back home, alongside the change in leaf colour associated with this season, October is the peak of the breeding season for four of the six species of deer found in the UK, with red, fallow, sika and reindeer all rutting at the moment. The peak of this activity tends to be at dawn and dusk, but the males will continue to call and scrap throughout the day and night. You can find out more about these species, their rutting behaviour and now also listen to their rutting calls on the respective deer species profiles. If you're heading out to watch or photograph the deer rut this year, please give them some space - these are big animals, pumped up with testosterone, and for their safety and yours, it's sensible to keep your distance. Before you head off, please check out the British Deer Society's Code of Conduct for deer watching/photography, which John Johnson, Jules Cox and I put together a couple of years ago.

October is the peak month of the deer rut. If you're out and about in woodland and heathland this month, please keep dogs on leads and give the deer some space. - Credit: Marc Baldwin

If you're interested in the other wildlife to be found this month, including the fox in-fighting, the science behind the leaf colour change and salmon migration, check out my Wildlife Watching - October article.

Website news

After nearly two years of research, I'm making good progress with the Chinese water deer article and the first part has now gone live. Part two is waiting in the wings and will go live in the next few weeks, while the third section is in proofing. I have just made a start on the fourth part. In addition to these sections going up, I have added a number of calls to the respective deer sections and some new audio to the fox communication article.

In the news

A few of the news stories that caught my attention over the last few weeks include long-awaited protection for a native fox subspecies in California, an ambitious vision for beavers in London, and how gut microbes may hold the key to reversing brain aging:

London-based charity Citizen Zoo has ambitious plans to see beavers return to the city's waterways. - Credit: Marc Baldwin
  • Breeding brains. Researchers at the Russian fox domestication project scanned the brains of foxes bred for tameness and aggression and found that both had significantly more grey matter than the control group, as well as enlarged prefrontal cortex, amygdala, hippocampus, and cerebellum. These findings are contrary to what we typically see in domesticated species and suggest we need to revise our view of how domestication leads to neuroanatomical change.
  • Beavering back. London-based conservation charity Citizen Zoo recently announced plans to bring beavers back to some of the capital's waterways. The charity has now started the London Beaver Working Group to facilitate collaborative discussion around both encouraging natural recolonisation and proactive reintroduction, having identified some suitable sites.
  • Point of no return? A depressing new study published in the journal Nature in July suggests that the Amazon rainforest may now have reached the point of no return as deforestation continues to increase year on year and climate change results in more water stress and wildfires. In July alone, Greenpeace recorded nearly 5,000 fires in the rainforest.
  • Forefending foxes. Last month federal wildlife officials announced that the Sierra Nevada red fox would be given federal protection as its population is thought to have dropped to only 40 animals in area of California stretching from Lake Tahoe to south of Yosemite National Park.
  • Bowel to brain? Recent research from scientists in Washington has shed new light on cognitive decline and offers intriguing insight into potential treatments for dementia. The study found that a transplant of gut microbes (in the form of faeces) from young mice to old ones reversed some symptoms of cognitive decline. The old mice that received microbes from young mouse poo were able to solve mazes more quickly and remembered the maze layout more readily than the control group.
  • Plastic pollution. An analysis of the stomachs of Shortfin mako sharks caught off the coast of Taiwan found that about 10% had ingested plastic, either films or fragments. While a relatively low ingestion rate, these findings nonetheless provide more evidence of the pervasive nature of plastic marine debris.

Discoveries of the month

Flexible fornication. Badgers have different mating strategies at high vs. low population densities

Badgers (Meles meles) are a familiar part of Britain's fauna and, at least partly because of their role in the spread of bovine tuberculosis, they're among our better-studied mammalian species. Indeed, we now know a substantial amount about their social and reproductive behaviour and that they're one of only a handful of species that use the strategy of delayed implantation to help “decouple” mating from birth. In effect, this means they can mate at almost any time of the year (taking advantage of any opportunity) and yet still give birth in late winter to ensure their cubs grow up when natural resources are at their peak by pausing embryonic development.

In addition to delayed implantation, superfetation has also been recorded in badgers, where additional oestrous cycles during pregnancy release multiple ova and allow for non-synchronous fertilisation. In other words, badger sows can conceive while they're already pregnant and this can lead to the simultaneous occurrence of embryos at different stages of development in a single mother. In most other species, the presence of corpora lutea, which produce progesterone, triggers implantation and maintains pregnancy, preventing further oestrous cycles. Now, new data from a multinational team of scientists suggests that the way these strategies are employed varies according to local population density.

European badgers adapt their breeding strategy according to population density to maximise their reproductive potential. - Credit: Marc Baldwin / British Wildlife Centre

The research team, led by Nadine Adrianna Sugianto at the University of Birmingham, analysed 97 blood samples from sows of different ages and reproductive statuses living in a high-density population (i.e. 26-55 badgers per sq km) in Oxfordshire and compared them with previous studies at medium (25 badgers per sq km) and low-density (2-7 per sq km).

In their high-density population, oestradiol was high during spring among unmated sows, dropping off sharply in summer and then remaining low through the autumn and winter, suggesting that the mating period was restricted only to spring. Additionally, the weak oestrogen oestrone was secreted continuously, but peaking in autumn and remaining high until the summer. This suggests that badgers secrete oestradiol to control the spring oestrus, while oestrone is continuously secreted throughout the period of delayed implantation to sustain blastocysts until implantation occurs in winter. There was no difference between breeding and non-breeding females in terms of sex-steroid levels during late winter, indicating that females were able to breed while suckling.

Overall, when comparing their data with those from studies conducted at lower densities, the biologists observed that at high densities there was a single main peak in reproductive receptivity during spring, while a second late-summer oestrous is seen at medium density, and multiple cycles occur throughout the summer in low density populations. The breeding season brings with it risks, particularly as boars fight for access to sows, suggesting a selective advantage to having more mating periods when there are fewer badgers around. Writing in General and Comparative Endocrinology last month, Sugianto and her colleagues suggest that, at high densities, opportunities for mating are everywhere, resulting in frequent copulations, and thus fertilisation is pretty much assured. At low density, however, additional receptive windows during delayed implantation can help improve the chance of conception. This flexible hormonal strategy helps badgers adapt to a range of different environments that support different carrying capacities.

Reference: Sugianto, N.A. et al. (2021). Alternative reproductive strategies provide a flexible mechanism for assuring mating success in the European badgers (Meles meles): An investigation from hormonal measures. Gen. Comp. Endocrinol. 310: 113823. doi: 10.1016/j.ygcen.2021.113823

Driving down deer-vehicle collisions

As the nights draw in, many of us find ourselves commuting in the dark, and this puts us at higher risk of encountering a deer crossing the road. This is especially the case during the autumn, when many species rut, and when your route takes you through farmland or forest. Every year an estimated 42,000 to 74,000 deer are hit by vehicles on UK roads, and that's likely to be a significant underestimate as many go unrecorded. In the US, the situation is graver, with some 1.2 million deer hit, 10,000 people injured and an estimated 200 fatalities. In addition to the human and cervid cost, such accidents also push up the price of motor insurance.

Many routes, such as this busy A road through the New Forest in Hampshire, have signage warning drivers that the route is a high risk one for deer crossing. Unfortunately, drivers readily get used to the signs and tune them out. - Credit: Marc Baldwin

You may have noticed signs along some roads that highlight the route being a high-risk one for deer crossings, but an issue with this approach is that people quickly get used to them and filter them out—a phenomenon known as “driver behavioural habituation”. In an attempt to help reduce the number of collisions, a team of Danish researchers at Aarhus University's Department of Bioscience analysed 85,333 records of deer-vehicle collisions (DVCs) collected over the 17 years between 2003 and 2019 in the country, looking for patterns that might help identify hotspots.

The results, published in the Journal of Environmental Management last month, don't reveal anything earth-shattering, but they do contribute some solid data that should help improve our ability to identify and target DVC hotspots. Roe deer (Capreolus capreolus) accounted for the vast majority of collisions (90%), followed by fallow (Dama dama - 6%) and red (Cervus elaphus - 4%), although the dynamic changed through the dataset and by 2019 the chance of a red deer being involved in a DVC was seven times higher than it was in 2003. Most DVCs occurred in arable areas for roe, and forest for both fallow and red. Just over two-thirds involving fallow and red occurred on larger roads (more than 6 m / 20 ft. wide), while only about half of collisions with roe happened on these larger roads. Drivers were most likely to hit a deer of any species in early May, corresponding to the peak dispersal period, and again in autumn, corresponding to the rut for red and fallow.

The probability of a DVC increased with proximity to farmland, woodland, heathland and water bodies, being lower in built-up areas. The chance of a DVC was highest at 05:00 and 20:30 and lowest between 10:00 and 15:00, with the likelihood of hitting a deer being at least five times higher at dusk/dawn compared to during the late morning and afternoon. The authors suggest that travel between resting and feeding sites, which tends to happen at dawn and dusk, increases the risk of DVCs, and point to other studies that have found woodland fragmentation increases the chance of such accidents in red deer.

In their paper, the team advocate the establishment of a warning system that is flexible according to the location, time of day and time of year. So, rather than having signs up all the time that drivers get used to and filter out, it would be more effective to have a system that alerted drivers on particular routes at specific times when a collision was more likely—during autumn evenings, for example, but not during the daytime. Such an application, along with targeted deterrence and fencing, could provide a simple and cost-effective solution to reduce roadkill.

Reference: Mayer, M. et al. (2021). Understanding spatio-temporal patterns of deer-vehicle collisions to improve roadkill mitigation. J. Environ. Man. 295: 113148. doi: 10.1016/j.jenvman.2021.113148.

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