Seasonal Update - May 2019


After a balmy end to March, the first week of April felt like a return to winter, with overnight frosts, ice, and snow across much of the country. This about-turn in the weather was courtesy of low pressure bringing air from the Arctic. The following week saw a switch back to mild conditions, with temperatures in the mid-teens Celsius in the south-east and 19.6C (67F) recorded in Suffolk on 8th April, before another flip back to Arctic air and a drop in temperatures for another week. A gradual change began to set in around the middle of the month and the result was an uncharacteristically warm bank holiday/Easter weekend, with the mercury hitting 25.5C (78F) in Gosport, Hampshire on Saturday. Easter temperature records were broken for both Northern Ireland and Edinburgh, peaking at 21.7C (71F) and 23.4C (74F), respectively. The seasonal average for late April is 10C (50F) in the north and 13C (55F) in the south.

While few people complained about the glorious bank holiday weather, it came against a series of sit-in protests in London and Scotland by a group of climate activists called Extinction Rebellion (XR). The socio-political movement, relatively little known until the start of the action, was protesting  the British government’s lack of action on climate change and pressing Theresa May to meet with them to discuss her plans to reduce greenhouse gas emissions. The group have demanded that the government reduce carbon emissions to a net of zero by 2025 in a bid to head off the social and economic disaster some predict climate change will bring. Unfortunately, while some have described XR’s demands as “ambitious”, the Energy & Climate Intelligence Unit, which broadly supports tough action on greenhouse gasses, points out that the timeframe they propose “has absolutely no chance of being fulfilled”, requiring, as it does, the complete cessation of flying and the removal of some 38 million cars and 26 million gas boilers in the next six years. At the time of writing, however, the government had agreed to meet with XR representatives.

Along with calls to take more robust steps to tackle climate change, National Gardening Week and Hedgehog Awareness Week aim to get people to help the wildlife on their doorstep. Helping hedgehogs in your neighbourhood is surprisingly simple. You can leave out a bowl of fresh water in your garden day and night. You can cut a small (15cm x 15 cm / 5x5 in.) hole in your fence to allow hedgehogs access between gardens. You can check overgrown areas before strimming. Check out the British Hedgehog Preservation Society’s award-winning video for more information.

Hedgehog Street. The award-winning short video on the troubles hedgehogs face in modern Britain along with some advice on how you can help. Credit: British Hedgehog Preservation Society

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.

Interested in the wildlife to be found this month? Check out my Wildlife Watching - May page.

Discoveries of the Month

Landscape barriers are no big deal to dispersing red squirrels

Many of us are familiar with squirrels in our local woods, parks and even gardens. In most cases, these are the “grey invaders” and few of us are fortunate enough to encounter wild red squirrels on a regular basis. This situation is not unexpected given that population surveys suggest the distribution of reds in the UK has shrunk by some 70% since the 1940s as the grey population has expanded. Indeed, the Red Squirrel Survival Trust estimates that, without significant conservation effort, the red squirrel could be extinct in the UK within a decade. In a bid to redress this decline, the red squirrel was added to Schedules 5 and 6 of the Wildlife & Countryside Act (1981), which provides the highest level of wildlife legal protection, prohibiting any deliberate disturbance including inflicting injury or death, trapping, or destroying dreys.

Red squirrels (Sciurus vulgaris) are more arboreal than greys, meaning they spend more time in the trees and less on the ground, which had raised concerns that habitat fragmentation may affect their ability to disperse. - Credit: Marc Baldwin

Along with legal protection, considerable additional resources have been directed at studying red squirrels to understand more about their ecology. An important element of population management and conservation is their potential for dispersal. As the species spends most of its time in the trees, concerns have been raised that habitat fragmentation is a serious threat to the viability of red squirrel populations, isolating populations, reducing the potential for animals to move out and establish colonies elsewhere, and restricting gene flow between populations. New research from Finland suggests, however, that the picture may not be as bleak as first thought.

Working in an urban and rural area of Finland, Turku and Ostrobothnia respectively, University of Turku ecologist Suvi Hämäläinen and her colleagues trapped and radio-collared 59 juvenile red squirrels between 2012 and 2015. The squirrels were tracked using portable receivers about once each day between early June to late September in a bid to understand their dispersal behaviour. At the same time, the researchers mapped the surrounding landscape to assess whether the class of habitat had an effect on their dispersal pattern.

The squirrels collared in the rural expanses of Ostrobothnia dispersed over much greater distances than those born in Turku. Indeed, most urban squirrels remained within 2km (1.2 miles) of the trapping site, while the rural animals moved up to 16km (10 miles) away. This is not unexpected -  many mammal species have higher densities and lower dispersal distances in urban areas where food and shelter tend to abound. Of more interest to the researchers, though, was how the animals crossed different types of habitat. The tracking data show that the squirrels tended to avoid unfavourable habitat, such as wide open fields, preferring to move through forested and edge habitat. When fields were crossed, the squirrels took bigger steps than when crossing preferred habitat. Interestingly, however, when the researchers looked at the straight line dispersal distance, they found it was largely unaffected by the landscape structure. Writing in Ecology and Evolution last month, Hämäläinen and her colleagues explained:

For example, even though the squirrels avoided fields in the rural landscape, the amount of open areas did not affect dispersal distances in this region.In our study, the largest agricultural gap crossed by a juvenile individual was, at its narrowest, an approximately 3 km wide open field, with a river running in the middle of the area and no circuitous route available. This highlights the great movement potential of red squirrel juveniles.”

A Red squirrel (Sciurus vulgaris) running along a woodland track. - Credit: Marc Baldwin

The researchers concluded that landscape structure has an obvious influence on the movement patterns of juvenile red squirrel, but apparently only a limited effect on dispersal distance. This is good news for squirrel conservation programmes because it suggests that habitat fragmentation may not be that significant a barrier to squirrel gene flow, albeit that forested and edge habitats seem to actively promote squirrel dispersal.

Reference: Hämäläinen, S. et al. (2019). The effect of landscape structure on dispersal distances of the Eurasian red squirrel. Ecol. Evol. 9: 1173-1181.

Breeding owls help keep orchard “pests” in check

A Ural owl (Strix uralensis). - Credit: Tatiana Bulyonkova

Many of you will have heard about the recent change to bird management licenses by Natural England, meaning landowners can no longer shoot certain bird species (16 species in total, including most corvids such as crow, rooks and magpies) without applying for a dispensation, which requires provision of proof that the birds are damaging their livestock or crops. This story made the mainstream news and social media last month when Chris Packham, a vocal champion of this change, received death threats and suspicious packages. This serves to vividly underscore the conflict that exists when dealing with species we consider to be “pests”.

Despite the controversy, there is little argument that some species have the potential to inflict significant financial costs to farmers, running into the hundreds of millions of pounds each year. Where possible, however, “natural pest control”, i.e. leveraging predators to reduce pest numbers, is seen as an increasingly viable alternative to guns and poisons. To that end, new research from Japan’s Aomori Prefecture suggests that owls have a role to play in helping manage the populations of some small mammals that are considered orchard pests.

Between 2000 and 2007, a team of researchers led by Chie Murano at Iwate University assessed the impact of Ural owls (Strix uralensis), a relative of our tawny owl (Strix aluco), on the population of field voles (Microtus montebelli) in apple orchards where they damage roots and bark during the winter months. The biologists surveyed the diets of the owls breeding in tree hollows in the orchard and established nest boxes in a bid to encourage more owls to breed. The vole population was then monitored through the year and compared to orchards where there were no breeding owls.

Murano and her colleagues found that voles made up just over 80% of the prey fed to owl chicks over the duration of the study and the presence of breeding owls had a measurable effect on orchard vole populations. Indeed, the data suggest nesting owls in orchards reduced vole populations by between 53% and 70% within breeding territories during the chick rearing period in April compared to those orchards without breeding owls. Interestingly, there was also significant suppression in May and November in owl-occupied orchards and, in their paper to the Journal of Applied Ecology, the researchers explain:

One factor contributing to the strong suppression of vole numbers in May and November may be the direct predation by Ural owls in April. Extrapolating from the results shown in Table 2, a pair of breeding owls prey on approximately 150–300 voles during the rearing period, which is before the vole spring breeding season. The considerable decrease in the number of voles of breeding age in April could potentially impact the population later in the year.”

Field voles are often considered a pest to foresty for the damage they can do to roots and bark, particularly during the winter months. - Credit: Milo Bostock

Additionally, the authors suggest that another potential factor in reducing vole populations could be the indirect effect of owls as predators – driving rodent dispersal, reducing rodent activity and lowering survival/reproductive rates. Overall, Murano and her colleagues concluded that:

Supporting native raptor inhabitation in agricultural areas could be an option for [integrated pest management] and could contribute to sustaining regional biodiversity.”

Reference: Murano, C. et al. (2019). Effectiveness of vole control by owls in apple orchards. J. Appl. Ecol. 56: 677-687.

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