Seasonal Update - January 2019


Welcome to 2019! I’d like to take this opportunity to wish all my readers and their families a very Happy New Year. I hope you had a good festive break and thank you for coming back!

December was a fairly wet month, with temperatures above average down here on the south coast. Indeed, as I sit here and write this, I’m reminded that I stood and watched a bee visiting the flowers on the honeysuckle in our garden on the afternoon before Christmas Eve as temperatures reached a balmy 14C (57F). December also saw some heavy rain and strong winds that brought widespread flooding and the loss of some large trees. The “big day” itself was cooler, with temperatures only a couple of degrees Celsius above the seasonal average in the south and western parts of the UK; cooler still in the east. At the time of writing, the Met Office is forecasting a “Sudden Stratospheric Warming”, a rise in temperature of up to 50C (90F) in a just couple of days up 10-50km in the Earth’s atmosphere that results in the stratosphere collapsing into the polar cap and disrupting the westerly airflow, bringing easterlies to Britain. The east is a cold wind direction for the UK, suggesting that the weather is set to turn much colder in January.

If you’re interested in donating some of your time to help us better understand the wildlife around us in 2019, there are a couple of surveys underway this month that are looking for volunteers.

This year marks 40 years of the Big Garden Birdwatch. The goldfinch was the sixth most commonly reported bird during last year's survey; a striking recovery from their extreme rarity at the end of the 19th century, following years of being trapped as cage birds. - Credit: Marc Baldwin

Probably the most familiar of these is the Big Garden Birdwatch, run by the RSPB, that takes place on the last weekend of this month, the 26th to 28th January. You can sign up for the birdwatch now via the RSPB’s website.

Secondly, as I mentioned last year, the British Trust for Ornithology’s tawny owl calling survey is underway now. This survey is much more relaxed than the point survey they ran last autumn. Essentially, all they need you to do is stand in your garden, local allotment, park, wood, etc. for 20 minutes one evening a week and record whether you hear a tawny owl calling. The survey runs until the 31st March and the more weeks you can record for the better, but you can do as many or as few as you like; it also doesn’t matter if you miss some weeks. No calling is as valid a result as any other, so even if you’re pretty sure you don’t have tawnies in your neighbourhood I urge you to get involved and submit your findings.

Finally, if January does turn much colder and all you want to do is snuggle up inside with a cup of tea, you can still be helping wildlife by helping out with the Mammal Web team identify the species captured on the trailcam videos submitted to them. Just register on their website and you can start looking through trail camera stills and video, you then simply select what animals you see in the videos in the list on the same page – easy peasy.

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 are looking for people to organise cleans of their local beaches – details here. The Forestry Commission are running a series of events this month (full list here).

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

Discoveries of the Month

Moths give bats the slip with sound-absorbent wings

Bats are special mammals in many ways. Not only are they the only members of the class who truly fly, they mate while hanging upside down following some seriously impressive aerial acrobatics, and they track their prey and navigate their habitat using echolocation. As sound waves emanate from a source, they encounter solid objects in the environment and are bounced back. Echolocation is the process of using these reverberations (or “echoes”) to help judge how far away an object is and in which direction it’s moving.

In the case of our visual system, we rely on light reflected from objects around us to see; bats rely on sound reflected from objects around them to see in the dark. Bats emit a variety of chirps and squeaks during flight and listen for the echoes. Sound striking close objects will be reflected back sooner and be louder than sound striking a more distant obstacle. Similarly, by listening for changes in the phase of the echo, bats can determine the type of surface from which the sound was bounced back – a hard, continuous object (such as a wall) will produce a sharper echo than softer objects (such as foliage). New research by a team at the University of Bristol suggests that some moths cash in on the limitations of this feeding method to help them avoid the bats’ radar.

The cabbage tree emperor moth (Bunaea alcinoe) has a scale microstructure that appears to absorb sound, acting like a stealth coating that makes the insects more difficult for bats to detect with echolocation. - Credit: Bart Wursten (CC BY-NC-SA 2.0)

A team of biologists and engineers led by Zhiyuan Shen studied the wings of the cabbage tree emperor moth (Bunaea alcinoe) under a scanning electron microscope and noticed something interesting about the lamina covering the top and bottom of each of the overlapping scales. In their paper to the Proceeding of the National Academy of Sciences in November, Shen and colleagues note that the “double-perforated scale nanostructure” of the moth’s wings absorbed the ultrasound they fired at them, acting something akin to a stealth coating that prevents the soundwaves being scattered back towards the bat. A 3D computer model run by the scientists calculated that the scales absorbed about half the soundwave energy and, in their paper, suggest that the wings may be even more efficient than their model implies:

A real moth wing is composed of multiple layers of cover and base scales of different sizes, shapes, and degrees of overlap. The ultrasonic absorption coefficient spectra of a real moth wing could therefore be higher than the numerical estimated value here.”

Source: Shen, Z. et al. (2018). Biomechanics of a moth scale at ultrasonic frequencies. Proc. Nat. Acad. Sci. 115(48): 12200-12205.

Crafty caches: Arctic foxes choose memorable sites to store their leftovers

Many animals store food for later consumption. Indeed, this is a behaviour that even we humans engage in, with routine trips to the local supermarket or farm shop to stock up on supplies for the next few days. Historically, this behaviour would’ve helped our ancestors take advantage of periods when food was bountiful to see them through harsher times; this is how we see caching used by other animals, such as jays and squirrels.

Quite how animals find their buried food has fascinated biologists for decades. Memory seems to play an important role and it’s often presumed that the owner remembers the rough area of the cache and then follow their nose to the “loot”. A recent study on Arctic foxes (Vulpes lagopus) in Canada suggests that foxes may pick conspicuous landscape features to help them relocate their caches.

The Arctic fox (Vulpes lagopus) is a small canid of the Arctic tundra where food is scarce for most of the year. Caching of food when it is abundant is a crucial behavioural adaptation to this demanding environment. - Credit: Scott Weingart (CC BY 2.0)

A team led by Claire-Cécile Juhasz at the University of Moncton studied the caching behaviour of Arctic foxes in the Sirmilik National Park Nunavut on Canada’s Bylot Island. During the summer, the park plays host to a large nesting colony of some twenty thousand pairs of greater snow geese (Chen caerulescens), the eggs of which are an important food source for the foxes. The researchers identified 48 fox caches on their study site and paired them with a randomly selected site 50 metres (164 ft.) away. The cache and their paired sites were then subjected to a statistical analysis that looked at eight environmental variables, including the depth of the permafrost, moss cover, soil and herbaceous cover and the vegetation height, specifically the height of grass hummocks.

Moss, soil and rock cover had no impact on whether foxes chose the location as a cache site, neither did the depth of the permafrost (which affects how easy a soil is to dig). Juhasz and her colleagues did find, however, that the hummock height was correlated with cache probability. Indeed, hummocks located at cache sites were twice as tall as those near the randomly paired sites and this was particularly striking at the small scale (less so when viewed at the large scale over the whole site). In their paper to Polar Biology last year, the researchers suggest that the foxes use tall hummocks like sign posts:

“… a tall hummock could be used as a simple visual cue at a small spatial scale (e.g. 5 m in our study design) that foxes memorize to recover caches for later consumption.”

Studies like this help us to better understand how this species utilises crucial seasonal food resources, which is of increasing importance given that some populations of Arctic foxes, particularly those on the Scandinavian mainland, appear to be in serious decline.

Source: Juhasz, C-C. et al. (2018). Picking the right cache: caching site selection for egg predators in the arctic. Polar Biol. 41: 2233-2238.

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