Seasonal Update - June 2019

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Welcome to the start of meteorological summer. After a glorious – in fact, record-breaking - Easter bank holiday weekend and “not bad” early and late May bank holidays, some models are suggesting we will once again see some warm and dry weather over the course of the next three months. Indeed, this spring has been very dry for much of England, and here on the south coast we’ve had very little rain over the last month.

While many of us will be hoping for another balmy summer like much of the UK experienced in 2018, prolonged hot and dry conditions can be a significant problem for our wildlife. Last year, hedgehog rescue centres reported record numbers of dehydrated animals, and a similar pattern has been observed so far this spring. I’ve said this before, but it’s worth reiterating: if you can leave a shallow bowl of clean, fresh water out in your garden day and night in dry weather it can quite literally be a life saver to your local wildlife. Ideally, place some pebbles in the bowl so they break the surface, allowing insects such as bees and butterflies to land and drink without the risk of drowning.

Drowning in water bowls and watering cans isn’t the only danger our pollinators face in hot weather. Many people assume that balmy conditions are good for bees, and while this is true to a point, these insects can struggle in prolonged hot weather because parched flowers offer little food. Indeed, the results of the 2018 “BeeWalk” survey, run by the Bumblebee Conservation Trust, suggest that last year was a bad one for our bees. The report showed a decline in reports for seven of our commonest bee species, the ninth consecutive year numbers have declined. It seems that the very cold start to 2018, courtesy of “the beast from the east”, meant bees emerged from hibernation later than normal and the queens got off to a slow start producing workers. Subsequently, the long, hot summer reduced their food supply, wilting and parching flowers. The report wasn’t all bad news, with four uncommon bee species appearing to do better last year than in previous surveys, but the Trust is concerned that our bumblebees could encounter long-term problems in the face of more frequent heatwaves, which we’re likely to see with climate change.

There's lots of thirsty wildlife around during the spring and summer months. Water is often more important than food, particularly to any pregnant hedgehogs you may have visiting, so please leave a shallow bowl of water in your garden overnight if you can. Ideally place some stones in the bowl so they break the surface and provide a surface for pollinators to alight in order to drink without the risk of drowning. - Credit: Marc Baldwin

There’s a lot happening in the natural world at the moment (check out my Wildlife Watching - June page for full details) but there are a couple of things in particular that merit special attention.

The first is that we’re now well into the birthing season for hedgehogs and many females will have hoglets now. Please take extra care when working in your garden, particularly around leaf piles, hedges and log piles, to avoid disturbing nests. Hoglets are at risk of being abandoned or eaten by their mother if she’s disturbed, and any disturbance within the first three weeks after birth can be disastrous. If you do uncover a nest, please recover it immediately and contact your local hedgehog rescue for advice.

Secondly, June is the peak month for our deer to give birth to their calves (red and sika), fawns (fallow, muntjac and water deer) and kids (roe). A facet of deer behaviour is that youngsters are left lying in secluded spots until they’re strong enough to follow their mums and/or re-join the herd. Consequently, if you come across a baby deer curled up in the vegetation, please do not touch it unless it’s in imminent danger. The mother knows where it is and will return periodically to suckle and clean it. Simply leave it where it is and walk away. Contrary to popular misconception, it is very rare for a mother to abandon her fawn, but interference can stress the fawn and/or bring an angry mother (sometimes a group of angry females) running in your direction.

May and June are the peak months for male stag beetles being on the wing. These unmistakable insects are declining in Britain and to better understand their current distribution, the PTES are looking for records of males or females or either species (dead or alive), so please report any you find. - Credit: Fran Pregernik (CC BY-NC-ND 2.0)

There are also a few wildlife surveys taking place this month that could really use your help. We’re in the middle of the main stag beetle “flying season”, when males are on the wing, particularly during the late afternoon and evening, looking for females, and there are a couple of projects looking for information on your sightings. The Peoples Trust for Endangered Species are running their annual Great Stag Hunt survey, that allows you to easily record sightings via their website. I encourage everyone who sees a stag beetle anywhere in the UK to record it via the PTES site; at the time of writing just over 1,400 had been logged. More locally and, perhaps, more niche, is Ellie Mayhew’s study on the genetic diversity of stag beetles in the New Forest. Ellie is after dead stag beetles from Hampshire and the Isle of Wight until mid-August and you can find out more by e-mailing her or following the study on Twitter (@NFStagBeetles).

If you’ve been watching the latest series of Springwatch you may already have come across the Beyond the Backdoor survey being run by the BBC, British Trust for Ornithology and Open University. The survey is very straightforward and takes only about five minutes to complete. All that’s required is answering some questions about your garden and the wildlife therein. The aim is to gather a picture of how we use our gardens and what kinds of things we do to encourage nature into what amounts to the largest “nature reserve” in the country. At the time of writing just over 40,000 people had completed the survey (myself among them), which is a fantastic response, but they need more. The survey is open to any UK resident. (Please note that the survey does require you to provide your postal address for garden mapping purposes, but the survey is hosted on a secure site and the data collection bound by GDPR laws.)

As usual, the Wildlife Trusts have a series of nature-themed events up and down the country, as do the RSPB. If you feel like being proactive this month and live near the coast, Surfers Against Sewage is looking for people to organise cleans of their local beaches – details here. The Forestry Commission is running a series of events this month – full list here.

Discoveries of the Month

Plants can ‘hear’ and respond to passing bees

The leaves of _Mimosa pudica_ curl upon touch, illustrating how plants are senstivie (and respond to) their environment. - Credit: Teresa Grau Ros (CC BY-SA 2.0)

Until last night, I had planned to include some new research on estimating roe deer populations based on corpora lutea, but after Chris Packham mentioned this study on Springwatch it was too intriguing to pass up! The image of plants with ears is a rather comical one, but new research from Israel suggests that, despite lacking such obvious sound-gathering appendages, plants can detect the vibrations produced by some insects.

While once thought of as “unthinking” and “unfeeling” entities, plants are now well-known to respond to various aspect of their environment. Anyone with experience of growing plants will be aware that they respond to changes in light level and direction, generally growing towards a light source, and their response to chemicals and even electricity in the environment is well documented.

The response of plants to mechanical stimulation, both direct touch and vibration, are among the earliest documented behaviours. Indeed, in 1665 Robert Hooke described how Mimosa pudica, a perennial member of the pea family, folded its leaves when he touched it. In the late 1970s Charles, Prince of Wales, told journalists that it was very important to talk to your plants and that they respond when spoken to, suggesting they can respond to even subtle vibrations in the air. New research by a team led by Marine Veits at Tel-Aviv University’s School of Plant Sciences and Food Security nicely demonstrates that not only is this true, but also that the response can be very rapid.

Veits and her team exposed beach evening-primrose (Oenothera drummondii) to a variety of different sound recordings at different frequencies and measured how the petals vibrated and the sugar content of the nectar the flowers produced.

When the plants were exposed to silence nothing happened; the petals didn’t vibrate and there was no change in the nectar composition. Similarly, when played recordings of mid- and high frequency sound (i.e. sweeping from 35-34 kHz and 160-158kHz, respectively) although the petals vibrated the nectar content remained the same as the control. When they played low frequency sounds (i.e. sweeping 1kHz to 50Hz), however, they noticed something remarkable; the sugar content of the nectar increased. They also recorded the sound of a bee visiting the flower (around 200-500 Hz) and played that back with the same result – the sugar content of the nectar increased by around 4%*. These results were consistent among the 650 flowers the researchers tested and rapid, with plants responding within just three minutes of “hearing” the sound of a passing pollinator.

In their paper – currently awaiting peer review on bioRxiv – the team posit:

The petal vibrations that we measure could be picked up by mechanoreceptors, which are common in plants, and have been shown to respond to vibrations with similar amplitudes. We hypothesize that the flower serves as the plant’s external “ear” in terms of receiving sound pressure.

New research suggests that plants can detect the vibrations of flying insects and respond within minutes to produce more sugary nectar. - Credit: Patty O'Hearn Kickham (CC BY-NC-ND 2.0)

The specific mechanism by which the plants detect these vibrations isn’t known and Veits and her colleagues have more studies planned to try and understand the subtleties of the interaction. This study nonetheless highlights how ecology is full of connections and there’s still much to learn about even very familiar interactions such as bees buzzing around your flower beds.

Reference: Veits, M. et al. (2019). Flowers respond to pollinator sound within minutes by increasing nectar sugar concentration. bioRxiv. doi 10.1101/507319.

* There is some discrepancy in this value. In the paper the authors state that “average sugar concentration was 20% higher in flowers exposed to pollinator-like frequencies”, but Figure 1 of the paper shows an increase in sugar from about 16% to 20% (i.e. an increase of 4%). Additionally, in an interview with National Geographic one of the study’s authors, Lilach Hadany, reported the sugar content increasing from 12% to around 20% (i.e. an 8% increase). The paper doesn’t give the raw nectar concentrations, so it is not possible to confirm which percentage increase is correct. Regardless, we know that bees can detect changes in sugar content as low as 1%, implying that even a 4% increase is significant.

Australia’s marsupials are learning to avoid foxes

Since its successful introduction to Australia in 1871, the red fox has spread widely and now occupies all of continental Australia bar the northern arid and tropical regions; it occurs across the southern two-thirds of the continent, at least 18 offshore islands, and even penetrates into the hot deserts of the interior when seasonal conditions permit. As one might anticipate for a non-native predator, particularly one that’s highly adaptable behaviourally and has a catholic diet, the spread of the fox has been associated with a decline of several native vertebrates. Indeed, the method and impact of fox colonisation of Australia has led the IUCN's Species Survival Commission to rank them in their top 100 worst exotic invasive species. The Global Invasive Species Database states:

Foxes play a vital role in ecosystems in which they have evolved, but can cause devastation in those where they're non-native, such as in Australia. - Credit: Marc Baldwin

The damage to Australian wildlife since European settlement has been catastrophic. At least 20 species of Australian mammals have become extinct. This represents about one half of the world's mammal extinctions in the last 200 years; a further 43 species are judged to be either endangered or vulnerable.”

Foxes seem to have had the biggest impact on small to medium-sized birds and mammals (i.e. those in the 35g/1.2oz. to 5.5kg/12lbs range), this predation seemingly having severely limited both their abundance and distribution. A significant problem, we now know, is that native mammals are largely naïve of foxes and haven’t evolved strategies to cope with a highly opportunistic predator in their midst. In other words, they haven’t evolved to recognise the foxes as a threat and run away or hide. In a fascinating paper published in Global Change Biology last month, however, biologists at the University of Sydney suggests that this might be changing.

Jenna Bytheway and Peter Banks, both at the university’s School of Life and Environmental Sciences, studied the behaviour of free-living northern brown bandicoots (Isoodon macrourus) at four bushland sites in Australia, two sites where foxes had been present for more than a century and two where foxes were absent (more than 250km/155 miles from the nearest population). The researchers setup a series of “scent stations” at the sites, where fox urine was applied to a feeding station baited with peanuts and monitored by a trail camera, and recorded the number of visits by the local bandicoots. The data revealed a striking difference in behaviour between the two populations.

In the area where bandicoots were allopatric with foxes (i.e. lived without them) there was no difference in their response to the treatment, so they were just as likely to feed at a station tainted with fox urine as one treated with water. Where the two species were sympatric (living together), however, bandicoots visited the fox scent stations in only 30% of observations. Moreover, during visits to the scented stations, the bandicoots were significantly more wary - about three times more vigilant than they were at unscented stations, and spending about 20% less time feeding.

Overall, these data suggest that bandicoots can overcome predator naïveté, learning to recognise foxes as potentially dangerous and taking steps to avoid them, although it may take many generations for this behavioural change to become established. The recent reclassification of the population of this bandicoot species as “stable” in 2016 implies this response is in some way effective. What we don’t yet understand is how this mechanism evolves – is it learned or innate? – and this is something Bytheway and Banks want to investigate further, explaining in their paper that:

Understanding the mechanism driving bandicoots to overcome naiveté has important implications for the management of this species, in particular, how we can aid predator recognition in allopatric populations if the fox distribution expands to these areas.”

New data from the University of Sydney suggest that brown bandicoots that have been living in areas with foxes for a century or longer are evolving to recognise them as a predator, offering hope for their conservation. - Credit: John O'Neill (WikiMedia Commons)

Reference: Bytheway, J.P. & Banks, P.B. (2019). Overcoming prey naiveté: Free‐living marsupials develop recognition and effective behavioral responses to alien predators in Australia. Glob. Change Biol. 25: 1685-1695.

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