Seasonal Update (April 2023)

Mid-spring is typically a vibrant affair, with longer days, warmer weather and new life/growth everywhere. - Credit: Marc Baldwin

It's mid-spring and the beginning of the lighter evenings. The origin of this month's name seems to be somewhat lost to antiquity, although we do know that this month was named Aprillis, possibly derived from the verb aperire, “to open”, April typically being when buds and flowers begin to open. The month was originally the third in the Roman calendar, added by King Numa Pompilius about 700 BP.

Weather update

March started the same way February ended for most of the UK - high pressure dominating the weather, bringing cloud, the odd shower and temperatures widely around the seasonal average. As we progressed through the first weekend and into the second week, things turned much colder, with daytime highs widely in low single digits and sub-zero nights. Around the middle of the week many parts of the northern and midland UK saw snow - we even had a dusting along the New Forest coast - before conditions became wet and windy into the second weekend. Heavy rain and gusts of 50 mph (80 kph) battered the south coast. During the brief cold snap, temperatures fell to -15.8C (3.6F) at Kinbrace in the north Highlands on morning of 8th, while the Scilly Isles started the day on 11C (52F). Temperatures rebounded quickly and all but the northern isles were in mild air by the middle of the month, with temperatures widely in double figures, even overnight in the south-east. The latter half of the month was marked by a succession of low-pressure systems bringing heavy rain, gale force winds and mild temperatures widely in double figures, even at night, in much of England and highs of 16C (61F) in the south-east, interspersed with cooler air that saw overnight frosts during the final weekend of the month.

After a dry February, March saw some significant rainfall combined with strong winds. - Credit: WX Charts

After a very dry February across most of southern England and Wales, the tables turned in March. A southerly jet stream meant last month was wet in the south but much drier in the north. London, for example, had seen 60% of the monthly average rain fall for the month by the second weekend, and Shoeburyness in Essex reached 75%, while most of Northern Ireland, northern England, and particularly western Scotland had seen only 3-4%.

Outside of the UK, storm “Juliette” brought torrential rain, heavy snow and 76 mph (122 kph) winds to Mallorca, causing significant disruption to Spain and the Balearic Islands into the start of March. Snowy scenes were to be found in the Sierra Nevada mountains of California in early March, accumulating nearly four metres (13 ft) of snow in seven days. Snow even fell to low levels in the state near the coastline. France was at the other end of the spectrum, having suffered an exceedingly dry winter off the back of an exceptionally hot and dry summer, resulting in significant shrinkage of the Lorne, France's longest river, and the government imposing water restrictions early last month.

As well as being a wet month, March was also widely mild, particularly through the second half. - Credit: WX Charts

The temperature reached 45C (113F) at Magiscatzin on 2nd March, the earliest 45C ever recorded in North America climatic history, and only a day after the earliest 40C (104F) in US history. Hundreds of temperature records were also broken in China. Beijing, for example, recorded 27.9C (82.2F), which is just over five Celsius (9F) warmer than the early March record. In Thailand, dozens of recording stations in the north and north-east were near or at record highs for the second half of last month with Loei recording 41.2C (106F). Australia started the month with hot conditions in the west, and several records were broken. The village of Mullewa had a hot night with a low of 29.3C (84.7F), the highest on records in March.

Indonesia experienced torrential rain early in March, triggering landslides that buried houses on one of the remote islands in the Natuna region, killing at least 10 people while more than 40 are still missing.

Website news

The UK sharks and rays page was updated to include the first record of the smalltooth sandtiger (Odontaspis ferox), a specimen of which washed up on a beach here in Hampshire last month, and some minor updates have been made to the other shark related content. Additionally, a new water deer section is now online, looking at the species' rutting behaviour.

News and discoveries

Chernobyl's canids. On 26th April 1986, some 120,000 people living in the city of Pripyat and surrounding area were forced to abandon their homes when a design flaw in the nuclear reactor at Ukraine's Chernobyl power plant caused the core to melt. While a 2016 report suggested the area wouldn't be habitable for humans for some 20,000 years, the wildlife has thrived in our absence. Now, a new study of blood samples collected from dogs living in and around the site between 2017 and 2019 found them to be genetically distinct from pet dogs elsewhere in the world.

A recent study suggests that where there are lots of black bear sightings, so too do there tend to be Bigfoot reports. It is proposed that the tendency of this species to stand on hind legs that might lead to misidentification. - Credit: Nathanael Coyne (CC BY-NC-ND 2.0)

Plastic pestilence. It's common knowledge that plastic is a significant and pervasive problem in our ecosystems, having been found virtually everywhere on Earth and in increasingly high concentrations. The list of problems that plastics causes wildlife is long, but now a specific disease caused by plastic, called plasticosis, has been described in Australian shearwaters. The researchers list extensive scarring of the digestive system and altered collagen prevalence among the symptoms. Interestingly, these were specifically associated with plastic ingestion; consumption of pumice didn't cause the same scarring.

Bearing up to scrutiny? Sightings of large hairy ape-like creatures living in forests have been reported by indigenous cultures for centuries, although what we commonly think of as “Bigfoot” can probably be traced back to the mysterious footprints described in a letter to the Humboldt Times in 1958. As endearing as the myth remains, most scientists discount the existence of such a primate and a new statistical analysis suggests that sightings in North America are strongly correlated with black bear sightings. It seems that for every 900 bear sightings in an area, one sasquatch report is likely to follow.

Bee-ing observant. Social learning, where an animal watches what someone else is doing and then utilises what it has learned for its own reward is now well known among animals, particularly birds and mammals. We have fewer data from insects, although new research led by Queen Mary University London has described this behaviour in bees. “Observer” bees were given the opportunity to watch “Demonstrator” bees opening a puzzle box using either red or blue tabs. When it came to their turn, the observers overwhelming followed the example set by the successful demonstrator.

Seasonal highlight - Grebes get going

Any avid followers of the BBC's SpringWatch series will have no doubt have heard reference to and probably even seen footage of the elaborate courtship dance of the Great Crested grebe. These ornamental-looking waterbirds are becoming an increasingly common sight on our ponds, flooded gravel pits, reservoirs, lakes and some coastal areas; an estimated 9,400 breed in the UK and, during winter, there are upward of 19,000 in the country. Indeed, they're now resident throughout most of England, Wales and Ireland, excluding the far southwest tip of the UK, central-southern Ireland, Northern Ireland and Scotland (although some birds spend the summer in eastern Scotland). This hasn't, however, always been the case, and there was a time when GC grebes were on the brink of extinction in the UK. GC Grebes were hunted on an almost industrial scale during the second half of 19th Century to sate a demand for feather decoration for hats, trims and coats. The hunting was sufficiently intensive that, by 1860, there were estimated to be only 42 breeding pairs left in the country. Two subsequent “protection acts” (one in 1870 and another in 1880) offered respite to the grebes and the population began to recover. Great Crested grebe populations are now monitored via the annual Breeding Bird Survey, which shows numbers are still increasing, but probably starting to plateau.

A Great Crested grebe in breeding (summer) plumage. - Credit: Marc Baldwin

Great Crested grebes are medium-sized water birds, weighing about 1kg (2.2 lbs) and with a wingspan up to 88 cm (just under 3 ft.). They are supremely adapted to life on, and under, the water, with a short femur, a long leg bones, and legs set well back on their body compared with other diving birds. The toe morphology of grebes is also unique, with each toe having separate and rather stiff skin lobes enlarging its surface. Only the inner parts of the toes are fused by webbing and it has been suggested that this arrangement may allow the toes to function as multiple slots during swimming, which would increase the efficiency of the power stroke. Indeed, grebes are so at home in the water that they appear very clumsy on land and have almost lost the ability to walk. Grebes also have considerable speed and manoeuvrability under the water. In a study of Grebe swimming mechanics, published in 2001, Chris Johansson and Ulla Norberg (at Sweden's Göteborg University) demonstrated that grebes swim underwater by kicking out to the sides and slightly upwards with their feet (not unlike a frog's swimming motion) while keeping their wings tightly at their sides to aid streamlining. The biologists reported an average swimming speed of around 1 metre per second (just over 3 ft. per second). Dives typically last for about 20 seconds, with pauses between dives at the surface of around 10 seconds.

Grebes live almost continuously in water and spend most of their time either hunting for food or preening. GC grebes are primarily piscivorous - i.e., their diet is mainly fish - with fish of up to about 7.5 cm wide by about 22 cm (3 x 8.6 in.) long tending to be taken. Small prey may be eaten underwater, while larger items are brought to the surface. These birds are often found on fishing lakes, but dietary studies conducted in the Netherlands suggests that they don't have a significant impact on the populations of the game fish in such lakes/farms. Grebes will also take invertebrate prey, such as crayfish, shrimps, molluscs and insects (the latter being most common during the breeding season, when small waterborne and flying insects are fed to chicks), along with the occasional frog or newt. Intriguingly, adult grebes have been observed eating helminth parasites, sometimes pulling them directly from the cloaca. Grebes also have a curious habit of eating their own feathers and it is believed that this may be associated with their ability to eat gut parasites. Overall, adults consume about 222 grams (8 oz.) of food per day, while juveniles require just over 100 grams (3.5 oz.).

Preening is an important activity and grebes spend a significant amount of their time engaged in it. Feathers may also be eaten to assist pellet formation. - Credit: Marc Baldwin

Second to foraging, preening is a grebe's most time-consuming behaviour. Feathers are fastidiously cleaned and greased with a preen gland-secretion. During preening, grebes also consume their own feathers; it's thought this may help them form and cast pellets (of indigestible food waste as seen in raptors such as owls) and also reduce their gut parasite populations. A study of grebes on Lake IJssel, in the Netherlands, found 8,718 feathers in stomachs of 407 birds, most (68%) of which were plucked from the breast or stomach and were particularly abundant during the autumn (less so during winter). Interestingly, the biologists found that the number of feathers ingested was related to the species of fish the grebes were eating; grebes eating lots of smelt (which leave little indigestible matter in the stomach) ate more feathers than those feeding primarily on perch (which leaves more fish debris in stomach). The authors suggest that the presence of the feathers adds additional material to the stomach that allows the grebes to form pellets of fish bones that can be coughed up (in the same way other predatory birds, such as owls, do). In doing so, they can also remove any parasites in the upper digestive tract.

It is perhaps their elaborate courtship behaviour for which Great Crested grebes are best known. Julian Huxley (Professor of Biology in the Rice Institute, Houston, Texas) was the first ornithologist to describe the courtship behaviour of GC grebes in detail in a landmark paper to the Proceedings of the Zoological Society of London during September 1914. There are many interesting facets of grebe interaction, but the two most Byzantine of these are the “Head-shaking Ceremony” and “Weed dancing”. The Head-shaking Ceremony ensues when the pair come together (often after preening or hunting); they face each other making a “cackling” call, turn heads in opposite directions, followed by each twisting their heads around and “tweaking” the feathers on their back (“habit preening”) on opposite sides to one another. One or both grebes typically have their head plumage extended during this “mirroring” display, which can last from a few seconds to a couple of minutes. After the head shaking, the pair separate and both may dive, returning to the surface with weed or twigs. Holding the material in their beaks, they swim rapidly towards each other (head-on), rising up on their haunches and treading water furiously while turning their heads in opposite directions. Mating must take place out of the water, typically on the nesting platform. (Watch courting grebes - link to a video on the WWT's YouTube channel.)

Nesting platforms are fairly basic aggregations of reeds and sticks, the bulk of which is below the water ensuring a moist and cool cup for the nest. Following successful mating, three or four (may be 2 to 6) eggs, each measuring about 5.5 cm by 3.5 cm (2 x 1 in.) and weighing 40 grams (1.4 oz.), are laid at two-day intervals. The eggs are incubated, with both parents taking turns, for about a month and the chicks hatch asynchronously in accordance with the interval between laying eggs. In areas where human disturbance is high grebes tolerate the approach of people closer to their nests than in less disturbed areas, but Verena Keller found that nesting success was lower on disturbed lakes in Switzerland than on less disturbed lakes. When disturbed at the nest an incubating bird gets up quietly and pulls material from the edge of the nest over the eggs before leaving. On disturbed lakes, however, although they may not be as prone to leaving the nest, when they do leave, they cover the eggs less often than in quieter spots. Leaving the eggs exposed means they're more vulnerable to predation (particularly by coots). It may be that leaving the nest uncovered may also make the eggs more prone to cooling, but there are data suggesting that the eggs are fairly tolerant to cooling, even if they are washed off the nest during a storm. Andre Konter studied grebes on Lake Ijssel and found:

While very young, the striped chicks are carried on the back of one parent from where they are also fed small insects. - Credit: Marc Baldwin

Due to the high resistance of eggs to cooling, they may even hatch after having passed several hours in cold water. In addition, grebes are capable to resume or continue laying quickly to replace lost eggs.”

Indeed, the grebes didn't just abandon nests/eggs during a storm; instead, they tried to save their clutch by re-building the nest and even recovering floating eggs out of the water.

The striking black-and-white striped chicks hatch out and, once they've dried out, they're quite lively and, rather than remaining under the parent as is common among birds, the chick climbs on to the parent's back. The chick will generally remain on the back of the parent incubating the remaining clutch; once all chicks have hatched, they are carried on the backs of one parent, while the other hunts for food. The chicks are unable to thermoregulate for themselves for the first couple of weeks and it is believed that the parent's plumage helps keep them warm. The chicks are fed small fish and insects and, after a couple of weeks of being carried by their parents, they are ejected onto the water where they continue to be fed increasingly large fish until they're fully fledged at around two-and-a-half months old. The more often the chicks are fed, the better their chance of survival. Mortality is highest during the first two weeks of life, during which time mortality may be as high as 50% (i.e., half die). Starvation, cooling and predation are the biggest threats, in that order—most mortality results from starvation, although some suffer hypothermia in bad weather. Predation is apparently rare and most reports are of Pike taking chicks although, as mentioned, coots will sometimes predate eggs. Grebes reach sexual maturity at two years old and can have significant longevity—the oldest bird on record was ringed as a chick in Russia and shot as an adult 19 years and three months later. Records aside, it seems few wild birds exceed 12 years old.

For a round-up of Britain's seasonal wildlife highlights for mid- spring, check out my Wildlife Watching - April blog.

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