Colour-ringed Waxwings

I went to see the Hessle waxwings this morning, where a flock has been present since last Friday. Straight away, I saw two photographers looking at a tree. I soon joined them and the 18-strong flock was there, in a small street-lining cherry tree, facing the strong westerly wind. The light was beautiful compared to my previous Waxwing sightings, most of the time in the depths of winter. The birds were quite mobile, trilling and moving from tree to tree before descending to the unlikely source of berries this time of year: hawthorns.

No supermarket car pars, but car dealerships this time.

The 18 strong flock. 

Berries, what berries?
Probably most hawthorns in the country were stripped of berries long ago. Not these. The leaves of some of them sprouting amongst last year’s crop of berries. The reason for the late berries could lay in the location of this hedge: a very narrow strip of land between the A63 and a busy local road on an industrial estate. Every time the waxwings descended to feed, roaring trucks on one side and fast delivery vans on the other, I feared for their safety. Photos don’t really convey the feeling of being there, the noise of the road and the wind, the feel of the acrid stench of the traffic fumes at the back of your throat. This stressful food location has probably kept the local thrushes and Woodpigeons away.

On the hawthorn: berries and fresh shoots.

Colour rings
Two of the waxwings had plastic rings with different colour combinations on their legs. The yellow plastic over metal of their right legs indicate that both birds are part of the 2019 ringing scheme by the Grampian Ringing Group. In fact, information supplied by Raymond Duncan from the Grampian ringing group indicates that both birds were ringed on the 7th December 2019, in Aberdeen. One of the birds, a female with white, black and red rings stayed put until the 5th of January at Aberdeen, the other, a male with light green over dark green and dark green ring was found in Thirsk (N Yorkshire) on the 30th December and 3rd of January. Waxwings move towards the UK at the beginning of winter, in large numbers when the berry crop in Scandinavia is poor, what is called irruptions, and then they move south and east through the country. Is it coincidence that both birds are together in Hessle? Although social birds, Waxwings are not known for forming strong individual bonds when they move about during winter. However, there are reports of the same birds returning to favoured spots in different irruption years, so the same individuals may meet again in these Waxwing hotspots.

The Grampian Ringing Group has many years of experience colour ringing waxwings: they have colour-ringed thousands of waxwings for over thirty years. This winter, their dedication has paid off with 100 ringed waxwings and some resightings across the country. Their blog is a treasure trove from everything waxwing including how to sex and age them. Resightings of colour ringed birds, particularly when the colour rings and their position can be ascertained, are crucial to follow the movements of Waxwings without need to recapture them.

The male was ringed in Aberdeen in December.

Female also ringed in Aberdeen in December.

Males, females and ageing
Waxwings of different sexes and ages appear similar at first sight, but they are subtly different. Examination of their plumage pattern can actually be used to age and sex them. Adults have their primaries edged with white and bright yellow, forming a ‘hook’, while young individuals have only one side of the primaries lined with white or pale yellow. When the wing is closed this forms a single line. First winter immatures also have a shorter crest. The ‘bib’ is larger and sharper in males, while the bib edges are diffuse in females. The yellow terminal tail band is wider in males. Males have over 6 waxy red feather tips, and these are longer in adult males, but there is some overlap between sexes. Females have a small number of smaller waxy tips. Some of these features are visible in flight, so you may want to have a go at sexing and aging your waxwings from photos.

The diffuse edge of the bib indicates this is a female.

After watching the Waxwings for a while, I went to their old haunts in Priory Park at Hessle. Trees lining the road between Sainsburys and Aldi supermarkets have been removed, but their favourite berry trees, rowans, are still there, of course, there wasn't a single berry left! 

Stonechat pairs in winter territories

Species like the Robin keep territories during the winter, with males and female individuals defending their own separate territories, while in the summer, territories are defended as a pair. There are some exceptions in which pairs defend winter territories, often in different areas that summer ones. One of these species is the Stonechat. In their wintering grounds on the coast and around the Humber estuary, it is frequent to encounter Stonechat pairs in the same area, feeding near each other and following each other, with no aggression (top shot, a pair at Alkborough, Lincolnshire, 11/12/2017). Of course, winter territory defence has nothing to do with reproduction, and often happens in areas that don't even hold breeding pairs in the summer. This unusual behaviour must offer some benefit to persist in the population, maybe allowing individuals to increase their chances of survival to predation or competition and to secure sufficient food resources.
A study of wintering Stonechats in the Negev desert (Israel), shed some light onto the behaviour. A total of 89 individuals were colour banded and followed through two wintering seasons. Their territorial behaviour was noted. The most surprising result of the study is that wintering Stonechat pairs are very fluid. Pairs often form after arrival to winter areas, and individuals rarely stay together all winter, instead pairs change frequently, with an average of just 4 weeks together per pair. In fact, none of the studied pairs stayed together all winter long and individuals arrived in the area and left at different times. This rules out that breeding pairs migrate together or settle on the same winter territory. Up to a third of individual are unpaired at any given time, but all associations are always between a male and a female. There were some aggressive interactions between members of a pair, which were commonly initiated by the male. Both males and females engaged in territory defence, with males more aggressive against intruders than females.

Male Stonechat at Kilnsea, 10/12/18.

Why pair in the winter?
If pairs are not stable, don't migrate together, or don't form in preparation for the winter season, what is the point in defending territories as a pair? Males and female stonechats feed on the same prey, therefore there may be a cost on sharing a territory during the winter, when food resources may be very scarce. A possible benefit outweighing the cost may be joint territory defence: two individuals are better spotting and chasing away conspecific intruders or detecting predators and defending the territory against individuals of other species with similar food resources. In this study, individuals spent a lot of time defending the territory against Mourning Wheatears, but there was no mention of differences when pairs or individual Stonechats were involved.

Another pair at Kilnsea (13/1/2020)

Why male/female pairs?
These results don't clarify why associations are not between two males or two females defending a territory. The authors speculate that as Stonechats are sexually dimorphic, even in the winter, there may be constraints that prevent two males from living peacefully in the same territory, and the increased male aggressiveness may mean two females may be unable to defend a territory against a male/female pair.

More information
Gwinner, E., Rödl, T. and Schwabl, H. Pair Territoriality of Wintering Stonechats: Behaviour, Function and Hormones. Behav. Ecol. Sociobiol. 34, 321–327 (1994).

Wintering Chiffchaffs

In the last month, I've come across a couple of wintering Chiffchaffs. The last of them this Wednesday on my way to work, the calling bird revealed it's presence atop a maple, busily feeding on the top branches. Although most UK warblers are breeding migrants, four species can be found during winter. Two of these are resident species, the Dartford and Cetti's Warblers. The situation is more complex with the Blackcap, which I've covered before, and the Chiffchaff.

Sewage plants and wetlands
Chiffchaffs are insectivorous year round, so they can't rely on garden feeding like Blackcaps during winter. Overwintering in Chiffchaffs was documented in the early 19th century, but this seem to involve very few birds. In recent decades, however, there seem to have been an increase in numbers, possibly aided by global warming. Ringing and recaptures have allowed estimates of around 100 individuals gathering in suitable sites. Chiffchaff winter survival depends on a steady supply of invertebrates (mainly midges, gnats and aphids) and sheltered sites where to roost. They appear to survive several consecutive nights with frost, so the increased temperatures may have more important effects on insect abundance, not actual survival of the birds. Suitable habitats include sheltered coastal areas, but they also use urban and suburban sites, especially near water, sewage treatment plants (where warmer water means an abundance of insects) woodlands and hedgerows. The Chiffchaff on the top shot, fed low on the marginal vegetation around an urban lake, East Park, Hull on 2/12/2013.

It's complicated...
The Chiffchaff is part of a species complex and its taxonomy has changed quite a lot in recent years. What was considered a single species now includes the Canarian and Iberian Chiffchaff, previously races now elevated to species level. The Chiffchaff proper is now divided into various races: the nominal race, collybita, breeds in the UK, whereas tristis or Siberian Chiffchaff, and Scandinavian Chiffchaff abietinus. The three races are very similar, differing in the tone of the plumage and subtle morphological features, and more notably, song and calls. Given this and the occurrence of intermediate forms between some of the species makes them very difficult to identify in the field.

Residents, migrants and winter visitors
It appears that the bulk of the UK breeding population of Chiffchaffs, belonging to the subspecies collybita, migrate south in the winter. In addition, there is very strong passage through the UK, especially in the autumn, mainly of northern European birds moving to winter quarters in the Iberian Peninsula, and Northern and Western Africa and these include a sprinkling of abietinus and tristis individuals. What about the winter birds? Where do they come from?

Ringing and DNA analysis
Ringing recaptures in the winter don't include locally breeding Chiffchaffs, suggesting that the winter birds are also migrants. Most of them appear to belong to the collybita subspecies, which breeds in western Europe and Southern Scandinavia. Recoveries of birds ringed in winter in Southern England have been made subsequently in N England and Denmank during the breeding season. Recently, DNA analysis has come to the rescue. It is possible to obtain enough material for DNA analysis from tiny feathers, dislodged when ringing birds. Sending these feathers for DNA analysis allows to discriminate between subspecies, as they have distinct DNA. Individuals captured in the south of England include some Siberian chiffchaffs confirmed by DNA. Over 20% of ringed wintering Chiffchaffs in a mixed woodland by a lough in Ireland was confirmed to be tristis and two individuals were confirmed as abietinus. So it appears that wintering Chiffchaffs include individuals from all three European subspecies, that once finding suitable locations during migration they settle for a while to feed. Ringing recaptures have found the same individuals wintering repeated years in the same location. Another intriguing feature of wintering Chiffchaffs is that males, which are larger than females, were the bulk of wintering chiffchaffs in the past, although females are increasingly wintering. There is still so much to learn on Chiffchaff migration, taxonomy and evolution.

More information

Clement, P. 1995. The Chiffchaff. Hamlyn Species Guides. pp126.

Clement, P., Helbig, A. J. and Small, B. 1998. Taxonomy and identification of chiffchaffs in the Western Palearctic. Br. Birds 91, 361–375.

Birds in Cheshire and the Wirral. A breeding and wintering atlas. Wintering Chiffchaffs. 

O’Mahony, B., Farrer, D. and Collinson, M. 2008. Genetic identity of wintering Common Chiffchaffs Phylloscopus collybita trapped in County Kerry in 2015. Ir. Birds 

Ray Meads Ringing Group A review of our wintering chiffchaffs.
Simms, E. 1985. British Warblers. The New Naturalist Series. Collins. 432 pp.

A wintering Chiffchaff

Warblers are generally migrant birds and we tend to associate them with warm weather and their songs heralding spring as males settle territories. One of the exceptions is the Blackcap, which I have covered before in the blog, which in the last half a century, has become a regular winter warbler in the UK, with some birds breeding in Germany migrating west to the UK, where they enjoy the food provided in garden feeders and milder temperatures. The other is the Chiffchaff is also a wintering warbler. Although not common, it winters around the coast and estuaries, especially in the South, and also industrial or sewage treatment sites where warm water encourages insects. In contrast to the Blackcap, The Chiffchaff is fully insectivorous through the winter so it doesn't benefit from berries or garden feeders. In the first day of the year I spotted a small bird in the garden and thought it would be a Goldcrest. Its relatively sedated moves (for a Goldcrest!) prompted me to look harder and I saw it was a Chiffchaff. A couple of days ago the bird, presumably the same one, was back I managed the top shot through glass, as it fed on the apple tree, where I've seen it several times. Some of the apple tree branches have an infestation of Woolly Apple Aphids, and this appears to be what the Chiffchaff is eating (you can see some fluffy colonies under the branch that the bird is sitting, to the left).

Mistle thrushes sharing the turf

There is a resident pair of Mistle Thrushes in my local park. The resident male has been singing occasionally since the end of November from a high post on the tallest trees. Mistle Thrushes' song is reminiscent of the Blackbird's but with shorter, more repetitive, mournful phrases that carry quite far. Up to five birds gathered on the grass before Christmas, and when the snow arrived the locals birds had to share the few clear patches of turf under the trees with a flock of immigrant Redwings and a lone Fieldfare in search of earthworms and other invertebrates. Mistle Thrushes are large and bossy, and if the other thrushes get too close, they are chased away without trouble. Resident birds have a head start in the breeding season. They know their patch and as soon as conditions are right they can start nesting right away.
 The male was singing again in the last few days without snow, while the female fed on the grass.

Mistle Thrush and Fieldfare

Mistle Thrush, Redwing (back) and Fieldfare (foreground)

The pair feeding on the snow

Male singing yesterday