April brought some of the best weather of the spring so far, frustrating for a country on partial “lockdown” over the COVID-19 pandemic and still seeing the tragic loss of nearly a thousand lives per day at the start of the month. Indeed, the Easter period and the run up to it saw each UK country recorded its warmest day of the year so far. In Porthmadog in Wales the mercury hit 22C (72F) in the week preceding the Easter Bank Holiday weekend, while parts of south-east England basked in 25C (77F) on Good Friday. All this unseasonable warmth was courtesy of warm air dragged up from the Azores as we sat between high and low pressure systems.
The second half of the Easter weekend saw an abrupt change in conditions, however, as the winds moved around to the north-east and temperatures fell back to around the seasonal average, in the mid- to high teens Celsius (mid-60s Fahrenheit). This lasted about a week, then the remainder of the month saw temperatures above average again, albeit frequently quite windy, with below average rainfall. Indeed, this April looks set to be among the, if not the, driest on record for England.
Fortunately, the strong winds we saw early in the month were largely confined to the pre-blossom season, so there was still a great deal of pollinator activity around the Easter weekend. Typically, warm and dry springs herald a bumper fruit crop during the autumn, if coupled with a damp summer. Indeed, April was the sunniest on record, with an average of 224 hours of sunshine; it was dry, too, with only 40% of the average rainfall. It remains to be seen if 2020 will beat the record for the sunniest British spring, currently held by 1948 which clocked up 558 hours of sunshine – that’s just over 23 days.
The advice from the UK Government remains that people can, and should, get outside for exercise once per day during this CV-19 outbreak, while keeping at least 2m (6ft) away from others who aren’t members of your own household. If you’re intending to get out and about to your local allotment, park or woodland for your daily exercise (bearing in mind that some police forces do not permit driving to such locations for exercise, despite recent guidance to the contrary), or even just plan on spending more time in your garden, please consider taking part in the People’s Trust for Endangered Species’ Living with Mammals Survey, which is running now.
If you’re interested in the wildlife to be found this month, check out my Wildlife Watching - May page.
In the news
News stories that caught my attention last month include some disturbing news about a bastion of British summer, socially-distancing amphibians and disgusted mice.
- A poor year for hirundinids? Last month, bird watchers reported thousands of dead swifts (Apus apus) and swallows (Hirundo rustica) in the streets of Athens, on apartment balconies in the capital, in the north, on Aegean islands and around a lake close to the seaport of Nauplia in the Peloponnese, according to an article in The Guardian. It appears that strong winds, low temperatures and rain over the north of Greece and the Aegean Sea at the start of April resulted in many birds exhausting themselves on their migration routes northwards.
- Social distancing can help reduce pathogen spread in newts, too. Researchers at the University of Tennessee’s Amphibian Disease Laboratory studying the spread of Batrachochytrium salamandrivorans (Bsal for short), a highly contagious fungal disease of eastern newts, have found that habitat structures that separate newts helps reduce the spread of this disease. This helps illustrate how habitat changes can have unintended consequences for disease transfer.
- Not all heroes wear capes. Soybean cyst nematodes (Heterodera glycines) are parasitic roundworms that cause damage to soybean crops, reducing yields by as much as 75% and costing an estimated $1bn each year. New research by the University of Illinois suggests that arbuscular mycorrhizal fungi - fungi that form special relationships with the roots of various plant species, including soybean - can prevent nematode colonisation, reducing it by as much as 80%.
- Mice show facial expressions. A team of neurologists at the Max Planck Institute of Neurobiology have become the first to show that mice have different facial expressions for different emotional states – as well as the neurological pathways that seem to trigger them. It turns out that mice pull different faces when they’re anxious or taste something bitter, or something sweet. Mice licking sugar solutions showed joyful expressions while those licking salt appeared disgusted.
Discoveries of the Month
A little birdie told me. Rhinos eavesdrop on their hitchhikers to avoid humans
Back in December, I covered a study that found human voices, even quite benign ones, such as that of a person reading a poem, caused cougars to avoid an area. To many wildlife biologists, the idea that many wild animals go out of their way to avoid people, particularly those species that suffer persecution at our hands, is not surprising. Likewise, as covered the month before, it is well known that animals can tune into the calls and behaviour of other species and use it to help them find food or, as was the case for grey squirrels in that November 2019 study, avoid predators. This month a study caught my eye that draws these two concepts neatly together: where one heavily hunted species uses the behaviour of another to keep out of our way.
The black, or hook-lipped, rhinoceros (Diceros bicornis) is one of five species of rhino known to science and one of only two found in Africa. Native to eastern and southern parts of Africa, black rhinos are classed as “Critically Endangered” by the IUCN following their eradication from nearly half the continent since the 1700s. Some estimates suggest that during the early 1900s there were several hundred thousand black rhino in Africa, while the current population is probably about 5,000, having recovered a little since the 2004 low point of 2,500 thanks to intensive conservation measures and captive breeding programmes.
Civil wars, habitat destruction and climate change have all had a negative impact on rhino populations Africa, but invariably the largest impediment to their survival, indeed, the survival of all rhino species worldwide, is hunting by humans – specifically, illegal poaching. Historically, rhino horn was used to make ceremonial daggers and wine cups in the Middle East and China. Currently, however, it is the apparently insatiable demand for their horns for use in traditional Chinese medicine that means rhinos still very much face the prospect of extinction.
Rhino horn is believed, erroneously, to be able to cure fevers, improve sexual stamina and fertility, detoxify the body and even bring people out of comas. The rhino’s horns are sheaths of keratin—the same structural scleroproteins from which hair, nails, hooves, feathers and even calluses are made—that grow from bony protuberances on the skull. There is no scientific evidence that rhino horn is any more worthy of the accolades bestowed upon it by some Asian cultures than your fingernails would be.
As a result of intense poaching, rhinos have good reason to take a ‘better safe than sorry’ approach to keep out of the way of people, and new research from zoologists Roan Plotz and Wayne Linklater at the Nelson Mandela University in Port Elizabeth, on South Africa’s Eastern Cape, suggests that rhinos can use the alarm calls of red-billed oxpeckers (Buphagus erythrorynchus), a member of the starling family native to the savannah of sub-Saharan African that feeds on ticks that parasitize a number of large savannah herbivores, to detect the approach of humans more quickly. Appropriate for a bird whose Swahili name is Askari wa kifaru, “the rhino's guard”.
Over a two-year period, Plotz and Linklater studied the behaviour of 51 adult black rhino located in Africa’s oldest proclaimed nature reserve, Hluhluwe-iMfolozi Park just north of Durban. The rhino observations were split into two groups depending on whether the rhino encountered had a GPS transmitter (which allowed the researchers to track their movements) or not. The number of accompanying oxpeckers was recorded in each of these two groups and the differences between the sightings of rhinos with and without tags and birds were plugged into a computer model.
The zoologists found that the presence of an oxpecker on a rhino thwarted their approach much sooner than if the rhino was lacking a sentinel. Indeed, when rhinos were without a bird they failed to notice the field assistant strolling up to them in nearly a quarter of experiments, while animals carrying at least one oxpecker detected the human every time. Moreover, the oxpecker’s alarm call typically meant that their hosts became vigilant when a human got to within 61 metres (200 ft.), which was nearly four times further away than rhinos without Askari wa kifaru spotted the intruders.
Based on observations of the rhinos’ behaviour when the oxpeckers called, the birds only suggest danger is near and not what that danger is or where it’s coming from. In their paper currently in press with the journal Cell, however, Plotz and Linklater write:
“Rhino almost always (95% of occasions) re-orientated to direct their vigilance downwind and never at the approaching person. Thus, oxpecker alarm calls do not include information about the direction of the threat, only its proximity, and rhinos continuously evaluated wind direction to know the direction of their sensory ‘‘blind-spot’’ and greatest vulnerability. Hearing an oxpecker’s alarm call, rhinos almost always assumed they were being stalked from downwind.”
The observation that the rhinos turn to face downwind was a particularly interesting finding of this study. We know that large carnivores, such as lions, don’t hunt from downwind, while human hunters do. (Indeed, this is a tactic that has been shown to increase hunting success as much as six-fold.) This, coupled with the fact that there are no reports of oxpeckers alarm calling at large carnivores, raises the tantalising, albeit circumstantial at this stage, prospect that the evolution of oxpecker alarm calls is a recent event that may have occurred in response to human hunting, and could potentially help rhinos reduce their susceptibility to poachers.
Reference: Plotz, R.D. & Linklater, W.L. (2020). Oxpeckers help rhinos evade humans. Current Biol. 30: 1-5. doi: 10.1016/j.cub.2020.03.015.
Dances with wolves. Could reintroducing wolves help suppress roe deer?
Britain has had a rather turbulent history with the wolf (Canis lupus). Archaeological evidence puts wolves in Britain as far back as the Pliocene (5.3 – 2.5 million years ago) and suggests they were quite widespread, which is supported both by Roman and Saxon chronicles and by the many wolf-related place names. Widely persecuted by farmers and aristocrats alike, King Edward I was probably the first monarch to pass an extirpation order on the wolves in his kingdom during the late 13th century, and bounties remained in many counties until the early 19th century.
Nobody is quite sure when the UK’s last wild wolf was killed. Some sources propose that Sir Ewan Cameron shot the last one in Scotland during 1680, while others suggest it was a hunter called MacQueen who presented the head of Scotland’s last wolf to the Laird of MacIntosh in 1743. In England, the suggestion is that the extinction of the wolf occurred at some point during the late 1400s, under the reign of Henry VII, although sporadic references in the literature continue into the 1500s. In Ireland extirpation orders were passed in the early 1600s resulting in the complete removal of the species during the late 18th Century; in his The History of British Mammals, Derek Yalden gives the last record as coming from Mount Leinster on the Carlow/Wexford border in south-east Ireland around 1786.
Over the years, there have been several calls to reintroduce wolves to Britain and the conservation charity Rewilding Britain notes that “There’s no ecological reason why wolves can’t live in Britain – there is enough habitat and wild prey”. Many of these arguments for reintroduction centre around the wolf’s ability to control large herbivore, specifically deer, populations, many of which have increased significantly, in part in response to an absence of any significant predators. We have seen that wolves can certainly influence the behaviour and recruitment of deer populations in parts of Europe and North America, and some significant changes in landscape biodiversity have been recorded in Yellowstone in response to wolf reintroduction. Many conservationists hope something similar could be achieved here, and in 1986 a proposal was put forward to introduce wolves on the Isle of Rum, off the west coast of Scotland, to regulate the Red deer (Cervus elaphus) population. More recently, in 1999, Aberdeen University zoologist Martyn Gorman called for wolves to be reintroduced to the Scottish Highlands with a view to controlling the deer that were causing damage to the commercial plantations.
Here in the UK, it is the roe deer (Capreolus capreolus) that is our most widely distributed and probably most numerous cervid, and a new study from France has been looking at the role this species has played in the colonisation of parts of the country since wolves crossed the Italian border in 1992.
Between 2001 and 2017, a team of researchers led by Malory Randon at the Fédération Départementale des Chasseurs de la Drôme studied the populations of wolves and roe deer in a 31 thousand hectare (77 thousand acre) area of the west Vercors mountain range in south-eastern France. The scientists looked at deer abundance and the size of 422 kids (fawns) across two contrasted areas of the site; one in the wolves’ core area that was intensively used, and a second that was on the periphery of their range and visited only occasionally.
The data, published in Population Ecology last month, show that, controlling for other factors, roe deer population growth was lower in the core area than the periphery, and began to decline in 2001. Following a very harsh winter in 2004/05, both roe populations fell, but the one outside the wolves’ core range recovered more quickly than the one inside it. Indeed, the researchers noted that the core area population remained at a lower abundance for five years following that winter. In addition to the population-level effects, the average kid body mass was lower in the core area than in the periphery, although it should be noted that this was less striking than has been reported in other studies and may not be an influence of the wolves per se.
Now, it’s not unexpected that a large predator would have an impact on the population of one of its prey species but, while the study could not establish whether wolf predation was additional or compensatory (i.e. whether it played an active role in reducing numbers or merely took the number that were doomed to die of something else anyway), the particularly interesting finding for me was how rapidly roe deer adapted to the wolves’ presence. The data show that both areas had a similar pattern of roe population growth by 2011, suggesting that the impacts of wolf colonisation were most significant during a 10-year period following the establishment of the pack. Writing in their paper, Randon and her colleagues suggest that the roe deer learned to recognise wolf cues, helping them to keep safe, and that the wolves may also have turned their attention from roe to red deer as their pack grew in size, a shift we’ve seen elsewhere. The scientists conclude that:
“Our study highlights the importance of long-term studies as different phases were detected in this work after the arrival of wolves. Indeed, after a first period when differences in roe population growth rates between the two study areas were detected, we detected a 6-year period when differences in roe deer abundance between the two areas were detected, and after no long-lasting detectable effect of wolves on roe deer populations could be detected.”
Reference: Randon, M. et al. (2020). Population responses of roe deer to the recolonization of the French Vercors by wolves. Pop. Ecol. 62(2): 244-257. 10.1002/1438-390X.12043