Seasonal Update (April 2021)

April is a great month for blossom-hunting; and where there's blossom, there are usually pollinators. - Credit: Marc Baldwin

Despite a few chilly periods, February was an uncommonly mild month, with temperatures widely above the seasonal average, particularly during the second half. March started on a slightly cooler note, with temperatures ranging from 7 to 10C (45-50F) across the country on Monday. It was also misty, with the Met Office issuing a yellow weather warning for fog in Yorkshire, Lincolnshire and Nottinghamshire. As the first week progressed, most of England and eastern Scotland was plagued by persistent low cloud and mist. When the cloud finally burnt back in the strengthening spring sunshine, we saw temperatures creeping into the mid-teens Celsius (high 50s Fahrenheit).

The first weekend was largely bright and dry, but with a chilly easterly breeze. Mild days and cold nights were the order for the first half of the second week, with widespread frosts overnight. Tuesday evening saw the arrival of a deep low pressure into the west, which brought persistent heavy rain overnight into Wednesday and for most of the day. Daytime highs and night-time lows sat around 11C (52F). With the rain came unseasonably strong “spring gales”. Inland areas saw 50mph (80 kmph) gusts overnight Wednesday into Thursday, while the south and west coasts were battered by winds topping 70 mph (113 kmph) - 86mph (138 kmph) gusts were recorded at Capel Curig overnight Wednesday into Thursday. It remained windy into the middle weekend, although the rain (and at times snow) became more fragmented, which meant most of us saw some sunshine and cooler overnight temperatures. The strong winds continued into the second weekend.

March saw some very warm weather, with the highest early spring temperature since 1968 at the end of the month. - Credit: Taro Taylor (CC BY-NC 2.0)

A problem with such strong winds during spring is that they can strip tree blossom. Granted gales are more of an issue later in spring when much more is in blossom, but strong winds in March and April can impact some of the early flowering species such as ornamental cherry and blackthorn, in turn affecting both pollinators and fruit production. Growing blossom incurs a substantial carbohydrate drain on a tree that is simply too costly to regenerate; once the blossom has gone, it has gone for the year.

High pressure anchored to the west of the UK brought in a northerly airflow for most of the third week, resulting in largely calm conditions, albeit with a couple of bands of rain moving down the country on Tuesday. Temperatures were down a bit on the previous week, particularly overnight, with daytime highs around or just above the seasonal average, although the central lowlands hit the mid-teens. There was a stark temperature contrast across the country towards the end of the week, with Norfolk hovering around 6C (43F) while Edinburgh notched up to 19C (66F), which is remarkable for the time of year. By the end of the week and into the penultimate weekend, the winds had picked up again. The spring equinox was a cloudy and cool affair for most of England, although temperatures were well into double figures Celsius (high 50s Fahrenheit) even in the north east of England and parts of eastern Scotland.

The fourth week started on a cold note for some in the Midlands and north, bringing morning frost on the Monday. With high pressure crouched over the near continent, it was generally cloudy with bands of scattered showers moving eastwards. Tuesday afternoon saw the arrival of an Atlantic weather front that brought some more coherent bands of rain and strong winds, gusting to 60mph (96 kmph) in the north. Wednesday and Thursday were settled, while Friday was cool, windy and showery (some sleet/snow to low levels in the north) lasting into the weekend.

The final weekend was a broadly cool, cloudy and windy affair. A cold front swept across Saturday night into Sunday morning, bringing gales to most of the country, and we saw further rain on Monday in western Scotland, while the rest of the UK was dry and warm courtesy of air brought up from the Azores. This tropical airmass remained with us for most of the last week, ending March on an unseasonably warm 24C (75F) in south-east England. In like a lion, out like a lamb?

Outside of the UK, in the first half of last month, David Ige, the governor of Hawaii, declared a state of emergency after 60cm (2 ft.) rain fell in only 24 hours, causing catastrophic flooding on Maui and Oahu, and forcing the evacuation of hundreds of people. At the same time, two large storms tracked through the western US; one brought heavy rain to California, while the other moved into the Plains and Upper Midwest bringing severe thunderstorms and damaging winds in a wide area from Kansas to Minnesota. Australia also saw some of the heaviest rains in a century, with flooding forcing the evacuation of thousands of people in New South Wales during the second half of last month.

Despite the description "Mad March Hares", boxing takes place throughout the breeding season, although March and April are the best times to watch it owing to the lack of action-obscuring crops. - Credit: Natural England / Allan Drewitt (CC BY-NC-ND 2.0)

If you're interested in the wildlife to be found this month, including a look at the underappreciated mole, fox cubs appearing above ground,and the blossom season, check out my Wildlife Watching - Aprilpage.

In the news

A few of the headlines catching my attention this month (not necessarily all recent) include armour-plated eyes, climate warming and a rare marine mammal sighting:

A close-up of the left eye of a Whale shark (Rhincodon typus), showing the dermal denticles ("skin teeth") on the surface of the eye. - Credit: Taketeru Tomita / PLOS One (CC BY 4.0)
  • Armoured eyes. Researchers studying whale sharks have discovered that their eyes are covered with tiny dermal denticles, much like those found across the rest of their bodies. The suggestion is that this armouring of the eyes helps protect them from attack given that they lack eyelids.
  • Cunning cephalopods. A male cuttlefish living in an aquarium in Sydney was caught splitting its display colours down the middle, displaying half male and half female colouration. Quite amazingly, this little guy was showing the male colour to the female he was courting and the female colouring to a competing male on the other side to stop him becoming aggressive.
  • Return to sender. Dust blown up from the Sahara into France by strong seasonal winds brought with it high levels of radiation. Rather ironically, these radiative particles appear to have originated from nuclear tests carried out by France in the Algerian desert at the start of the 1960s, when the country was part of the French overseas territory.
  • Too hot to handle. A new report published in the journal Nature Geoscience suggests that climate change is pushing tropical regions to the limits of human tolerance. If global governments fail to limit the heating to 1.5C above pre-industrial levels, the tropical band stretching either side of the equator will be too hot and humid for humans to live in.
  • Pinniped peregrination. Earlier this month, Welsh Marine Life Rescue divers did a double take when they were called out to rescue what turned out to be an Arctic walrus spotted at Broad Haven South beach in Pembrokeshire. This appears to have been the first visit to UK waters in at least 12 years.

Discoveries of the Month

Colour me bad? Plumage colouration reflects hunting proficiency in tawny owls in poor vole years

When ecologists talk about the feeding strategies of animals, they generally divide them into two categories according to the number of different things they eat: generalists and specialists. Theoretically at least, these categories actually exist as a continuum, from “narrow-range resource utilising specialists” to “wide range resource utilising generalists”. In other words, some species will feed on an extremely narrow range of prey (think giant pandas and their bamboo), while others will take pretty much anything they can catch—foxes, for example. How such dietary patterns evolve and vary within species is still something we don't know much about. Now new research from Finland has shed some light on feeding specialisations in our most numerous owl species.

The rufous/brown morph of the Tawny owl (Strix aluco). - Credit: Marc Baldwin

The RSPB estimates there to be around 50 thousand breeding pairs of tawny owls (Strix aluco) in the UK and, while we tend to hear this species more often than we see it, tawnies come in two distinct colours: rufous (red-brown) and grey. These “colour morphs” appear to have a genetic basis and we're seeing some morphs becoming more prevalent under certain conditions. Over the past fifty years in Finland, for example, the rufous morph has been steadily increasing its prevalence and this appears to be associated with milder conditions. More widely in Europe, birds with this plumage colour are less likely to skip a breeding season when conditions are harsh, suggesting there may be a difference in hunting proficiency between the morphs.

In a bid to understand whether plumage colour was an indicator of an owl’s dietary specificity, Patrik Karell at the Novia University of Applied Sciences and colleagues monitored 38 tawny nests in a forest in Uusimaa, southwest Finland, between 2013 and 2018. Over the course of the study, each pair (well, father, as they do most of the hunting) delivered just over three kilograms (6lbs 10 oz.) of food to their nests during a breeding period, nearly 60% of which was mammalian prey. The data also show that while the mass of food provided to the nest wasn’t associated with the colour morph of the father, the diversity of the prey was. When mammalian prey was scarce, brown fathers were more likely to switch to birds to fill the gap, which wasn’t the case for grey morph males who continued searching for mammals.

Writing in the journal Behavioural Ecology and Sociobiology last month, the authors note that, as the climate has warmed, vole cycles have become less regular (i.e. unpredictable) and this may spell trouble for the grey morphs, which appear more dependent on small mammal prey. Karell and her co-workers conclude that:

“...if winters become milder and the small mammal abundance peaks become more irregular or absent, there is a risk that the mammal-specialised grey morph will decline in frequency, overridden by its brown generalist conspecific.

Source: Karell, P. et al. (2021). Specialist predation covaries with colour polymorphism in Tawny owls. Behav. Ecol. Sociobiol. 75:45. doi: 10.1007/s00265-021-02986-6.

Hare and now. Brown hares adjust their activity to reduce competition and encounters with predators

The Brown hare was once a common sight in rural settings of England, having been introduced from the continent about three thousand years ago, during the Iron Age. Despite being a non-native species, they are generally a welcome addition to the British countryside but changes in our farming landscape that have seen a move away from more traditional agriculture, coupled with persecution, has resulted in a significant decline in their population since the 1950s. Despite being generally less abundant these days they nonetheless remain widely distributed in the UK and represent an important prey species for several of our native predators.

Hares have been widely studied and we know a reasonable amount their biology and behaviour. We know, for example, that they're largely nocturnal or crepuscular (active at dawn and dusk), although they may be active throughout the day while the females are in season and in less disturbed locations. One element of brown hare ecology that's less clear, however, is how it adapts its behaviour to fit the prevailing conditions; specifically, how they reduce competition and avoid becoming someone's dinner. New data from a team of Italian and Egyptian biologists has shed some light on this subject.

Foxes and hares often share the same habitat and foxes can have a significant impact on their population in some situations. New research suggests that hares alter their behaviour to make it less likely they're going to encounter a hunting fox. - Credit: Don Sutherland (CC BY-NC-ND 2.0)

With the aid of remote cameras, the biologists, led by Emiliano Mori at the Istituto di Ricerca sugli Ecosistemi Terrestri in Florence, spent a year studying the activity of brown hares living in a conservation area in southern Tuscany. Part of the study site was fenced to exclude terrestrial carnivores such as cats, dogs, pine martens and foxes, while the remainder of the reserve being freely accessible to all. Over a total of nearly 3,000 camera trapping days (they were using 20 cameras, hence so may “trapping days” during the year) they amassed 266 records of hares, split roughly evenly between the fenced and un-fenced area.

In both areas, the hares were primarily nocturnal with activity peaking during the first part of the night. Within the fenced area, however, hares were also active at dawn and dusk and their activity did not depend on the phase of the moon, while those outside the fence were much less active on bright nights when foxes tended to be more active. When the researchers analysed their records of roe deer, a potential competitor of the hare, they observed that while the deer and hares were active at the same times of day, the hares seemed to avoid areas used by the roe—i.e. there was a spatial overlap of only 16%. Writing in the journal Animals, the researchers imply that the management of farmland areas to reduce deer and fox populations is likely to yield benefits to hare populations.

Source: Viviano, A. et al. (2021). Spatiotemporal overlap between the European brown hare and its potential predators and competitors. Anim. 11: 562. doi: 10.3390/ani11020562.

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