A

A

Sunday 20 February 2022

The Mock Nightingale In Winter

As I began writing this, the second storm of the week, Storm Eunice, was beating down onto this often windswept part of the Somerset coast. Out the window the only bird visible on the feeders is a male blackcap. With each energetic gust he clings onto the bird feeder as it sways and gyrates in the maelstrom, determined to feed on the fat balls no matter what a named storm throws at him.  How different this day is to Tennyson’s poem, The Progress Of Spring…


Across my garden! and the thicket stirs, The fountain pulses high in sunnier jets, The blackcap warbles, and the turtle purrs, The starling claps his tiny castanets.


It is mid-February and therefore a little early in the year to hear such warbles, yet Tennyson’s poem subtly sets the scene. 

In Britain, the blackcap is mostly referred to as a summer migrant. Their arrival from the end of March is heralded by its melodious song, which the poet John Clare called in his sonnet The March Nightingale “a rich and such an early song “.  While Gilbert White wrote on the 19th May 1770  “Black-cap sings sweetly…it is a songster of the first rate… called in Norfolk the mock nightingale".

And that is all well and good, but it’s still winter. While overwintering blackcap in the Mediterranean regions are known to sing outside the breeding season, the male and female blackcap visiting my garden since before Christmas have been very much silent. Come sun, rain, frost or wind the male blackcap has been visible most days, more often than not the only bird on the feeders,  whereas the presence of others - sparrows, starlings, tits and chaffinches - is one of safety in numbers. 

Blackcap are smart looking little birds too. Richard Smythe said of the male blackcap, “The cock-blackcap is a dull grey scrap of a bird with a smart, forward-tilted black cap”.  A scrap of a bird indeed! I’m not sure about that. I think this true warbler is a neat little chap with his sooty black cap and mostly uniform grey body washed with a watercolour tint of raw umber. While the male has been the regular visitor to my garden, his female companion with her chestnut cap has been less frequent. I’ve possibly seen her half as often as him, or more possibly she tends to spend less time at a feeder so I’ve probably just missed her while writing this.

Small numbers of blackcap have long overwintered in England, especially in the milder South West. Records go back to the 19th Century and possibly further, though unrecorded. Yet in the last few decades numbers have increased and reading a 2003 article in the online site Birdguides it notes around 10,000 blackcap now overwinter here, mostly in gardens.

Casting my mind back fifty years or so my interest in natural history, like many of my generation I suspect, was awakened by reading books such as Observer’s Book of Birds, which lists blackcap thus,  “This warbler is a summer visitor [April to October] though like the chiffchaff, it has been known to winter in the South West of England”. Another bedtime reading book back then (under the cover with a torch) was my Collins Pocket Guide To Nests and Eggs, a book singly failing to even mention overwintering blackcap, “…summer visitor, with range of garden warbler, but breeds locally further north in Scotland”. 

I saw my first overwintering blackcap around the turn of the Millennium. The reasons why overwintering numbers have gently climbed are still not fully understood, although climate change, weather patterns and available food are thought to play a part.  That article in Birdguides neatly summarises this, noting that it is the sheer number of blackcap “that now choose to spend the winter here, rather than their usual wintering areas in southern Iberia and North Africa.” Deeper into the article the town of Weston Super Mare, a few miles from me, receives special attention as a wintering blackcap hotspot. Which begs the question, ‘why do blackcap now prefer to spend their winters in Weston-super-Mare rather than the Costa del Sol or Morocco?’ 


Watching what I refer to as ‘my’ blackcaps in the garden on a winter’s day, I could be fooled into thinking these were simply resident birds, summer visitors from last year who for reasons of their own, (like increasing numbers of swallow now overwintering in England), decided it’s far too much effort to fly south for the winter when there’s a smorgasbord of food being laid on in this garden. Well that’s what ornithologists thought for a long time, and they, and I, would be wrong.  These birds, with a few exceptions, are not a resident population but winter migrants.

Back in the 1990s the mystery of why blackcap were flocking to Weston Super Mare (and of course elsewhere) was finally revealed. A Germain scientist, Professor Peter Berthold, and his team captured 40 Blackcap on the Somerset coast during the winters of 1988-1990. These birds were then taken over to his research station in southern Germany where they were observed and held until the following autumn when they began to show ‘migratory restlessness’ (or simply - the birds hop in the direction they want to migrate). Professor Berthold concluded that “in contrast to most of the Blackcaps breeding in southern Germany (which migrate [in winter] in a southwesterly direction towards Iberia and North Africa), the British birds he had captured orientated in the direction of the UK (northwest), meaning that the breeding origins of the UK wintering population were most likely to be in south central Europe”. In other words the blackcap I’ve been watching all winter have probably come from breeding areas of Germany, Poland or the Netherlands. And the birds I saw in the summer are now sunning themselves in North Africa and the Med. 

It must be a tough choice for a blackcap. One morning in October they wake up and ponder life’s big questions; shall I head south to my warm Mediterranean winter quarters? Or head northwest and be storm lashed next to the Bristol Channel? Foregoing to head south, those birds choosing to migrate to Somerset for the winter, are here for a reason. Seemingly part of the reason is food, or correctly, supplementary food we all put out in our gardens.

Studies by the British Trust for Ornithology ( BTO ) suggested that in British gardens the increase in overwintering blackcap coincided with the increased provision of wild bird food in our gardens from around the 1960’s. Not just quantity but quality. I remember as a child pestering my parents to put up feeders, all that was available was dusty floor sweepings of seed from the local farm suppliers or pet shop. Today there is a dazzling array of fat balls, suet treats, seeds of every description, with an estimated 150,000 tonnes of bird food sold annually. That’s a lot of food being regularly made available, providing much needed energy-rich feeding in the lean times over winter. Many resident birds have adapted well, tits, chaffinch and so on and have seen their populations increase as a result. In this regard, it is these birds known as generalists who are able to adapt to changes, feed in gardens, and potentially benefit from increased body condition, energy, survival and maybe come breeding time just be that much fitter. Didn’t Darwin have a theory about that or something? It seems blackcap are one of the bird world’s generalists, after analysis of the BTO’s Garden BirdWatch data found strong evidence that the rate and numbers of occupancy of gardens in winter [by winter migrating blackcap] is directly influenced by both supplementary food provision and temperature. 

One of the fascinating discussions at the moment is with Climate Change, which species will win out. A study by Van Doren et al said “[blackcap] is a migratory songbird thriving in the face of environmental change”. Climate change is making British winters warmer and all this food is providing vital mid-winter energy. Simple? Well maybe. 

I’m returning to my Weston Super Mare question – how do blackcaps in Germany know I’ve a garden overflowing with sunflower hearts? Have they a food miles map? Are the BTO providing fat ball Sat-Nav trackers? Does a lone blackcap find the sunflower hearts, pop over to Freiberg to tell his Germanic lady friend and a week later they’re back? I don’t think there’s a definitive answer here and the detailed mechanisms behind why birds alter inbuilt migratory behaviour is a wide-ranging topic of discussion, but not today. 

However bird migration routes are mostly genetically inherited. It could be argued then that this increasing trend in wintering blackcap in England was one of a slow burn from a few Victorian individuals being simply opportunist to a full on parent-to-offspring inheritance.  However, what is fascinating is that over time these winter migrants from Germany are showing subtle morphological changes. It seems that blackcap wintering in Britain have developed relatively narrower and longer beaks than those wintering in Spain, the assumption being this is a result of needing  beaks to be narrower and longer to simply get into the gaps in the feeders. There’s that ability to adapt and survive again. Additionally further German studies even suggest that over time the British wintering and North African wintering blackcap may develop into separate subspecies, and all because I’ve popped some fat balls into a feeder!

Why the overwintering birds do not stay here to breed and maybe grab an earlier more suitable territory isn’t known fully, though it seems that a tiny number of blackap are truly resident. One study found that only 6 individuals out of over 1000 studied in the UK one winter stayed put. But will this change? Patrick Barkham writing in the Guardian newspaper put forward a theory that with climate change [many species] birds will no longer need to migrate south in the winter. Why burn a lot of energy to find food when there’s food here. It’s an interesting thought as I fill up the sunflower feeder yet again and sit back to watch Mr Blackcap come and have his elevenses.

I’ve really enjoyed watching blackcap on the feeders this winter, and they are selective over which feeder they use too. My blackcap only feed on sunflower hearts and fat balls, rather than seed or other treats, and this ties in with other studies of overwintering blackcap. These studies show that when blackcap arrive for the winter they firstly prefer open farmland and scrub, and only later in the season, or during times of bad weather, will they come into gardens. Watching the male in particular, he has a routine. First seen in the fir tree beyond the garden, he will fly direct to the feeder of choice. Unlike other birds which flit back and forth into cover with each morsel, the blackcap remain at the feeder for a considerable amount of time, often many minutes. Either he is  sure of not being nobbled by the large female sparrowhawk resident in the area, or simply unawares. And because he stays out in the open so long it affords lengthy observation.  One thing I’ve noticed is that he tends to start feeding at one point and slowly move in a circular direction around the feeder until back to where he started.  So familiar has he become with coming to the feeders that on the rare occasions he doesn’t turn up (or I failed to observe him) I feel a real sadness. Where has he gone?

Well maybe they’re all feeding on mistletoe. I’ve noticed over the last decade that nearly every tree around here is now festooned with large verdant pom-poms of this parasitic plant.  Mistletoe does prefer mild moist climates and I do live in the centre of the preferred range for this plant, but especially during winter where once there were bare branches, those trees are now ostensibly evergreen. And I’m not alone. Since the 2000’s there have been suggestions that mistletoe is spreading faster than it used to in Britain, especially so in the less favourable eastern half of the country where previously established mistletoe populations have been slow to spread. Part of this might be due to warmer winters, but blackcap is a major culprit in this spread.

I’ve not tried this myself but apparently sticky mistletoe berries are not easy to eat, most birds avoid them. Another winter visitor, waxwing, will eat mistletoe and of course so will the mistle thrush (and other thrushes). But despite their name, mistle thrush are not great at spreading mistletoe as they swallow the berry whole, the seed of which is excreted about 30 minutes later often dangling below a branch trapped in the sticky excreta. Blackcaps however only swallow the berry skin and pulp, leaving the seed needing to be wiped off its beak on, well you guessed it, a branch, a perfect spot to let it germinate. And of course it’s an ever increasing circle if you think about it, mistletoe is a source of food during winter for blackcap, they help germination success, so more mistletoe means more berries to feed on over winter, fitter blackcap, I could go on.

All I know is that in the next few weeks these overwintering blackcap which have entertained me all winter will head back to their European breeding grounds, to be replaced by their summer-arriving cousins from north Africa, arriving fresh and ready to take up breeding territories with song.

So let’s hear it for the blackcap then. Though it still doesn’t answer my question about why on earth they chose to come to Weston Super Mare? 



Selected Reference : 

S. Vere Benson,  The Observers Book of Birds; Warne London (1972)

R.S.R Fitter and R.A Richardson  Collins Pocket Guide To Nests and Eggs. Collins London (revised ed 1968)

Smythe, Richard  A Sweet Wild Note: What we hear when the birds sing. Elliott & Thompson, London. (2017)

Witherby, H. F, Jourdan, F.C.R, Ticehurst, Norman F. and Tucker, Bernard W (1940) The Handbook Of British Birds, Vol 2. H.F & G Witherby, London (1940)

Fisher, James,  The Shell Bird Book. Ebury Press and Michael Joseph (1966)

Tennyson : The Progress of Spring.  – [fifth stanza] http://www.poetryatlas.com/poetry/poem/348/the-progress-of-spring.html

Flegg, Jim  Oakwatch : a seasonal guide to the natural history in and around the oak tree. Pelham Books (1985)

Charles S Bayne  Exploring England. Collins London (1944)

John Clare’s Poem The March Nightingale “and while the blackcap doth his ears assail” can be found in the book Midsummer Cushion ed. Anne Tibble. Ashington. Carcanet (1978) 


ON-LINE REFERENCES 

Birdguides (2003) : Wintering Blackcaps – Where Do They Come From and Why?

https://www.birdguides.com/articles/wintering-blackcaps-where-do-they-come-from-and-why/


BTO : Why we are seeing more Blackcaps wintering in Britain? 

https://www.bto.org/understanding-birds/species-focus/blackcap


RSPB : Blackcap Mirgation 

https://www.rspb.org.uk/birds-and-wildlife/wildlife-guides/bird-a-z/blackcap/migration/


Smithsonian (2021) : Bird Migration Patterns Are Changing—and Climate Change May Be to Blame

https://www.smithsonianmag.com/smart-news/bird-migration-patterns-are-changing-and-climate-change-may-be-to-blame-180979054/


Van Doren, B.M., Conway, G.J., Phillips, R.J., Evans, G.C., Roberts, G.C.M., Liedvogel, M. and Sheldon, B.C. (2021), Human activity shapes the wintering ecology of a migratory bird. Glob Change Biol, 27: 2715-2727. https://doi.org/10.1111/gcb.15597


Barkham, Patrick. Guardian. 25 Oct 2021 – Migratory Birds May Stop Flying South For The Winter.

https://www.theguardian.com/environment/2021/oct/25/britains-migratory-birds-may-stop-flying-south-for-winter


Oxford study

https://www.ox.ac.uk/news/2021-04-14-bird-feeders-have-reversed-blackcaps-migration-fair-weather-visitors-wintering


Mistletoe website http://mistletoe.org.uk/

No comments:

Post a Comment