Mistle thrush pairs defending berry trees

Several bird species hold territories during the winter, like Robins or Wrens defending their patch and singing through the winter. It is rarer that a pair will defend a winter territory. I have covered examples like Stonechats and Pied Wagtails before. The former usually include a male and a female, but they are unlikely to be a mated pair.

A pair of Mistle Thrushes near their cotoneaster tree. Northern Cemetery 30/11/21.

Earlier in the week I saw some Rowans heavy with berries along a street. A Mistle Thrush sat on a taller tree nearby. Then another individual flew from the berry tree, a pair! Later in my walk, I saw another pair of Mistle Thrushes near their defended cotoneaster (above). I then realised seen paired Mistle Thrushes in the winter before, near their defended trees. Are they a resident pair? Is a pair better than a single individual defending their berry larders?

             

Clockwise from top left, Yew, Ivy, Rowan and Holly ripe berries.

The berries

Mistle Thrushes are well known for their winter defence of berry resources. Holly is one of the most important defended trees in the UK, followed by Hawthorn, Mistletoe, Yew and, later in the winter, Ivy. At Hull, I've seen Mistle Thrushes defend Holly, Yew, Rowan, Whitebeam and Cotoneaster. Often the same trees are defended year after year.

Mistle Thrush on defended holly, one of an Avenues of Hollies at East Park defended by a pair, 23rd November 2021.

Mistle Thrush overlooking its defenced Rowan, 1st February 2021.

Mistle Thrush on General Cemetery on its defenced Whitebeam at Pearson Park. 17th October 2014.

Mistle Thrush on its defended berry-laden Yew.

A Mistle Thrush atop the church rooftop checks the yew opposite, on Cottingham Road Community Church garden. 14th November 2017.

Defence behaviour

Aggressive tree defence behaviour is spectacular: The Mistle Thrushes use their loud rattling or churring calls, repeatedly and chases other birds away from their tree. Most aggressive interactions involve repelling other Mistle thrushes, but also any other thrushes, like Blackbird, and various finches, Great Spotted Woodpeckers, Waxwings and even single Woodpigeons. Defence consists on chasing intruders, often silently and even if the birds were feeding on fallen berries under the tree. If there is a conflict then the individual might flick its tail and wings, their white underwings flashing, while churring persistently. Churring also occurs in flight during chases. Their defence is effective due to their large body size - they are the largest European thrush. Curiously Barbara and David Snow, who studied this behaviour in the UK note how the Mistle Thrush chooses who to attack carefully and it will chase only some species away so long as they are food competitors for the particular tree it is defending. For example Starlings are left alone in hawthorn and holly (whose berries they rarely eat) but chased from Ivy, which they eat. Greenfinches and Great Tits, are chased from Yew (they feed on the seeds) but not from Holly, which they don't eat. Eventually, after a few attacks, the local birds will learn to avoid the defended trees, and the Mistle Thrush just watches from a distance, and often this is how you'll find a Mistle Thrush, sitting on a vantage point near its precious tree.

Establishment of the guarded tree

Snow and Snow describe that the system of tree defence is established in October or early November, when song might be occasionally heard and other Mistle Thrushes are vigorously driven off until the territory is set. That way they can exclusively feed on these berries through the winter when they are needed. The defended trees become their winter larders, standing out on the landscape, packed full of berries when all other trees have been stripped out. Mistle Thrushes actually avoid feeding on the berries of their defended tree if they can, especially when the weather is mild and the ground is soft and they can rely on worms and other invertebrates. You need to pay attention to these trees full of berries later in the winter to recognise that the reason they are there is that a Mistle Thrush is just sitting atop a tree or aerial nearby, preening or resting. Unfortunately this effort will be worth nothing if a hard weather spell drives flocks of winter thrushes or Waxwings onto their area, then the Mistle Thrushes despite their best efforts may be unable to maintain their tree defence and lose their berry crop in a day or two. If the weather is mild, the tree can hold its berries until spring, and then, usually by the end of March, trees stop being defended. The Mistle Thrushes start nest building, often nearby. In the case of their defence of holly, the long-lasting berries, which can remain in the tree for up to nine months, are often used to feed their young. The hard work of defending the tree through the winter pays off not only to increase adult survival but as parental investment.

A pair of Mistle Thrushes near berry laden rowans at Auckland Avenue, 14th November 2017.

Pair defence

If Mistle thrushes stay to breed on the area near their defended tree, it would make sense that the pair defends the tree, rather than one individual. Snow and Snow describe how pair defence is more common and successful than single individual defence, although no data is given as to the proportion of pair defence. They say that "nearly all trees successfully defended throughout the winter were jointly defended by a pair of Mistle thrushes" and that  “pairs or individuals centred on a source of fruit which, if all goes well, will be defended through the coming winter.” In contrast, research on Mistle Thrushes defending Mistletoe clumps in woodland in Poland did not find evidence of pair defence. Could it be that pair defence occurs in some situations or for some berry sources and not for others? Anecdotal observations, however, suggest that members of a pair can defend different trees in the same area, and join forces if one of the pair loses their tree. On their article on Mistle Thrush defence Barbara and David Snow comment:

"When fruit territories are first established, in autumn, each defended tree may be guarded by a single Mistle Thrush or by a pair. It is probably common for members of a pair to establish themselves at neighbouring fruit-trees. Thus we had three cases where two Mistle Thrushes began by defending separate trees quite near to one another (60-180 m) and later, when one of the trees was stripped (as a result of the onslaught by Fieldfares and Redwings in the severe weather of December 1981), the two jointly defended the tree that still had fruit. In another case a pair of Mistle Thrushes jointly guarded the same holly tree from October or November in the two successive years, continuing throughout the winter in the first year but losing the fruit to invading Fieldfares and Redwings in the second year."

Snow and Snow indeed suggests that the same individuals, if they survive, may defend the same trees year after year, but their birds weren't ringed, so we can't know for sure. I'm surprised there is still so much to known about this widespread bird!

More information
Skórka, P. & Wójcik, J. D. Population Dynamics and Social Behavior of the Mistle Thrush Turdus viscivorus During Winter. Acta Ornithol. 40, 35–42 (2005).

Snow, B. K. & Snow, D. W. Long-term defence of fruit by Mistle Thrushes Turdus viscivorus. Ibis 126, 39–49 (2008).

Snow, B., & Snow, D. (2010). Birds and berries. A&C Black.

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).

Allopreening moorhens

I have only once before seen Moorhens allopreening, and I could not photograph the behaviour. This morning I was luckier. I saw the pair of Moorhens on the other side of the lake in my local park next to each other. One of them adopted the a posture reminiscent to the 'invitation to mate posture', although standing, with head tucked under the chest. The other moorhen then started preening its head and neck, while the first moorhen relaxed the posture. The preening moorhen then adopted the invitation position and the second one briefly preened it. The bouts of preening were not very intense, but directly followed the specific head under chest posture.

This clip shows how the moorhens take quick turns soliciting the preening, and how the preening itself appears rushed and rough at times one pulls the other's feathers.
 

Stock dove driving

Stock Doves are so intriguing. A combination of shyness and a superficial resemblance to feral pigeons makes them often pass unnoticed. Several times this spring I have watched them in flight, usually a pair, sometimes trios, with one of the doves flying right above another, their wings almost touching, but there didn't seem to be aggression in the behaviour. What are they doing?
 I might have found the answer today, reading an old article by Derek Goodwin. He describes a behaviour called 'driving' which is present in several members of the pigeon family, including the domestic pigeon. This is his description:

The driving cock follows his mate everywhere, often literally "treading on her tail". He pecks, usually in a gentle manner, but sometimes fiercely, at her head. If the hen takes wing he flies closely behind and above her. If she goes to the nest (domestic birds) the male stops driving.

Pigeon breeders thought that driving meant that the male pigeon wanted the female to go to nest, given that when the female goes to the nest the driving stops. Goodwin disagreed with this interpretation and thought instead that driving allowed the male to keep the female away from suitors, either on the ground or in flight.

In the two photos illustrating this post, a third pigeon was flying out of frame. I presume the male is the individual above, intercepting the female from the male.

Goodwin observations were consistent with this, as driving happened when other males were near the female, in particular during a period before egg laying and ended once the first egg has been laid, that is, a period when the female is sexually receptive, so that the behaviour is the way the male keeps the female away of competitors, and is effectively a form of mate guarding, as he put it 'It functions to prevent insemination of the female by males other than her own mate. Interference with copulating pairs is part of the same behaviour-complex as driving and has a like causation and function.' When, occasionally, driving was observed with just the pair involved, he thought that the male had succeeded in his driving: 

I have seen a pair fly up from some crowded feeding ground, and the male, who was at first driving hard in flight, swing out beside or in front of his mate as they got well away from others in the air, usually going into display flight as he did so.

More information

Derek Goodwin (1956) The Significance of Some Behaviour Patterns ofPigeons, Bird Study, 3:1, 25-37, DOI: 10.1080/00063655609475836.

Encounters of the Sparrowhawk kind

I treasure encounters with Sparrowhawks as they are quite secretive and alert birds which don't like being seen. Today I managed some sightings of a pair in my local park. First I heard a call 'kikikikiki!' and I saw a female landing on a tree. The view was quite obstructed and unfortunately, she flew off as I tried to get a better view. 

Then, a while later, in the same area I spotted the male. Not sure how, possibly a blue tit alarm call alerted me. He had some prey, what looked like a small bird, and was plucking it.

 He flew off, carrying the prey in his talons, and I wandered after him towards some big trees where he had disappeared. Then I saw the pair together, high up the crown of one of the largest trees in the park, a poplar (top shot). Fortunately the beautiful light made up for the distance to take some photos. The male started preening. I couldn't see if the female had the prey now. Male Sparrowhawks hunt for the female while she incubates.

The male at the top, smaller and with reddish tones in his plumage. The female at the bottom, all alert. Soon tree foliage will completely obscure views of these birds from the ground.

 On my way back from work I looked longingly at the poplar. No Sparrowhawks to be seen there. But then, beyond the tree, high in the sky, the pair was circling together, playfully chasing and soaring.

Woodpigeon mating

Although the Woodpigeon must be one of the most abundant and familiar British birds, a few days ago I was lucky to watch their courtship and mating at very close quarters, when a pair landed on the garden fence. I should have taken a video, but instead I ended taking a series of photos, which don't cover the full sequence. I saw, but did not photograph, the initial courtship feeding.

1. The male (on the right) had just fed the female, both move the bills, like swallowing. They are right next to each other and excited, note the contracted pupil in the male. The female sits down, crouching, inviting copulation.

2. The male mounts the female, balancing with wings open.

3. The male stabilises on top of the female, which remains motionless, with  wings spread (to make male balancing easier?).

4. Copulation, male flaps for balance, female leans forward lifting tail.

5. The male jumps onto the left of the photo, both partners (which are extremely alike in colour and size) fluff their neck patch and bow their heads in what looks like an aggressive display. These are woodpigeons in all their splendour, what amazingly beautiful birds they are!

6. The female actually turns away from the male, not a brilliant shot but shows how the neck patch feathers are raised. The pupil is very contracted.

7. The male remains in the post-copulation display.

8. Both pair members come together again and preen (I think the female is now on the right, and shows the initiative in caressing the male neck and head area).

9. The caressing carried on for a while.

Female magpie begging from her mate

The pair of Magpies must be around the egg laying stage. Only the female Magpie incubates, while her partner must feed her during this time. Females start begging for food to her partner around the time that they lay their first egg, noisily, wings flapping and uttering what has been described as the 'clear call'. The success of a pair of Magpies depends on how good the male is at keeping his mate well fed. A hungry female is more likely to take breaks from incubation, leaving the eggs exposed to predators (most likely Carrion Crows, according to T.R. Birkhead, the archenemy of Magpies).
 Yesterday afternoon, I heard this peculiar Magpie call repeatedly from the garden. The pair of Magpies were at a birch tree and one of them (the one on the top, likely the female), flapped her opened wings, chasing and begging to the other, quite indifferent, individual, likely to be the male. I took a video of this behaviour you can watch below (you might need to turn the volume up to hear the call).



More information
Birkhead, T. R. Studies of West Palearctic birds: Magpie 189. British Birds 82, 583–600 (1989).

A pair of bullfinches

Bullfinches are generally shy and unobtrusive, they tend to stay hidden in vegetation and show little. It helps to recognise their sad contact note. I see them around regularly enough, but good views are rare. That's why I got quite excited that a pair of Bullfinches, Pyrrhula pyrrhula, recently started to frequent the local wildlife garden, giving me an opportunity to become more familiar with their behaviour. I first noticed a female, funnily enough at the Big Garden Birdwatch. I heard a specially mournful version of their call, possibly she had lost track of her mate.

The hard to photograph female amongst the bushes

The next day, both were around, skulking in the trees and hedges, occasionally coming to the ground to feed. They stayed close to each other, but still called regularly. They appeared to be feeding on buds and Guelder Rose berries.

The male feeding on Guelder Rose seeds

Yesterday, the pair was about, feeding together on Sycamore seeds, the last remaining ones on a tree, and had to stretch and balance precariously on the branches to get at them. Despite their stockiness, they are quite nimble. They peeled the seeds using only their parrot-like bills, unlike goldfinches that have to hold the seed with their feet.

 Bullfinches will feed on buds in spring. In autumn they feed on tree seeds, like Ash keys, Birch and Sycamore. Bullfinches are seed predators of berry producing trees: they discard the flesh of the berry and feed on the seed itself.

Pair of Moorhens

There are now two Moorhen pairs in the park. They own each one end of the pond, a pair owns the island and the other the 'rock' with a couple of clumps of marginal plants. Today the island pair was very cosy, both individuals together, the one on the left preening around the neck of its partner. Moorhen males are slightly larger and heavier than females, so the larger individual on the left is likely to be the male. The Coot pair abandoned the park after their two failed breeding attempts on the stolen Moorhen nest.

Carrion Crow cawing display

I haven't blogged on Carrion Crows this year at The Rattling Crow, and that needs to be amended. So today, I bring you a sequence from this morning, when I documented a Cawing Display. This is a series of movements carried on when cawing from a prominent perch, often by territory holders. The whole body arches and bows as the same time that they call loudly, giving the impression that they put all their might into it. This pair were sitting initially close together and I thought they were getting ready to preen each other, but then they must have spotted an intruder in their territory, as they started performing the cawing display in amazing synchrony. Each display involved cawing and bowing three times, while fanning their tails, and keeping their belly feathers raised. I noticed that in many of the photographs (see the top one, in the middle of a caw) the nictitating membrane - which makes their eyes look cloudy - was drawn at the same time that they called, something that is only possible to notice with photographs.

The pair watching intently. Their tails are touching and slightly fanned and their belly feathers are also a bit ruffled.

The start of a caw.

The end of a caw.

The intruded came closer and both birds called noisily and gave it chase.

Carrion Crows pair for life, which is often not that long (average 4 years, with a maximum recorded age of 9) and the pair remains together all year round. Only territory holders breed, with one year old birds and non-territory holders often moving in a flock and intruding in territories in search of food, leading to squirmishes with the territory holders, in which both members of the pair participate.

More information

Coombs, Franklin (1978) The Crows. B.T. Batsford Ltd, London. 255 pp.

Canada geese head tossing

The Canada geese with a broken wing is now in the company of his partner in the park, who didn't leave with the flock in early March to their breeding grounds. He managed to retain two other individuals for a while - maybe offspring from previous years, as Canada Geese have long term family ties - but they ended up leaving. This morning, somebody started feeding the birds on an end of the pond, and I saw the pair of Canada swimming towards the feeding point. Broken Wing was leading his partner. He kept tossing his head every few seconds, and after a few tries I managed to capture the behaviour (above). It felt like a 'hurry up, follow me!' beckoning to female. Indeed, Canada Geese often communicate using head movements. I have covered the pre-flight head tossing, which is accompanied by much calling. When on land, and during the flightless phase of chick rearing during the moulting period, head-tossing by itself indicates readiness to walk or swim and is used especially when they are very motivated to move. Head tossing is very conspicuous due to the white cheek patch, and this is often directed to family members. Individuals head-toss when stationary, appearing to signal to other family members to follow them, including females to young goslings, and the signal is continued during movement. The direction at which the head is tossed is also informative, indicating the direction of movement. Even young goslings - who don't have the white patch - start head tossing in the first day after hatching, signalling their intention to move to other foraging patch. In a situation of threat, e.g. when a predator is located, this visual signalling allows parents to quietly direct their goslings to cover, avoiding attracting unwanted attention by acoustic signals.

More information

Jeffrey M. Black and James H. Barrow, Jr. (1985) Visual signalling in Canada geese for the coordination of family units. Wildfowl, 36, 35-41. Available here.

Snooze time for a Greylag pair

The large wintering Greylag flock in my local park has now disintegrated into pairs, which have moved onto their breeding areas. The last few times the flock was around there were many fights as males started to become very aggressive towards other males. There are now just up to three pairs remaining, sometimes just the one. Yesterday, they were resting with the resident Canada Pair in the lake island where they are less disturbed by dogs and people.
 This pair, is easily recognisable by the male's black bill tip. In ducks, swans and geese the thickened tip of the bill is called a nail. In grey geese, juveniles have a dark nail, while in adults the nail is pale (so I have named this unusual male Black Nail). They are illustrating that paired geese tend to stay close together and do the same things at the same time: rest together, travel together, feed together. Research on the semi-tame Greylag flock established by Konrad Lorenz in Austria, showed that bonded pairs also carry out complementary behaviours, for example males are vigilant while females are foraging or resting. Pairs that had successfully reared offspring together differed from unsuccessful pairs in that they showed more reciprocation: females are vigilant when male feeds more often than in unsuccessful pairs.
  Unlike corvids or parrots, in which mutual grooming is important to keep the pair bond, geese never groom each other, in fact, I don't think I have even seen a pair of geese in actual physical contact (e.g. roosting against each other like pigeons or crows do). Instead, they are social allies, they rely on each other's support against rivals or intruders, and carrying out ritualised triumph ceremonies afterwards. In the Konrad Lorenz flock, although successful and unsuccessful pairs had a similar within-pair distances (keeping within one meter of each other), when previously successful pairs failed a breeding attempt, they remained closer together, showing a tighter social bond.

Eyes open

Eyes half close

In this video you can see an aggressive male chasing away other geese in the flock (taken 27th February 2015).



More information
Scheiber, I. B., Kotrschal, K., Hemetsberger, J., & Weiß, B. M. (Eds.). (2013). The Social Life of Greylag Geese. Cambridge University Press.