Acrobatic Woodpigeons and helicopter seeds

The Woodpigeon stately presence might suggest that they are cumbersome birds, but Woodpigeons feeding on trees show that they are surprisingly acrobatic. Compared to their relatives the Feral Pigeons, Woodpigeons have shorter legs and longer tails, which give them more manoeuvrability when moving on branches. Today I saw a group of ten or so feeding on a cotoneaster tree. One of them swallowed one berry rapidly after another while keeping its head low by the bunch of berries, reminiscent of how pigeons drink, keeping their bills under water and swallowing the water directly. 

 Further ahead, three or four were eating seeds in a Sycamore - the ones that fly like helicopters - and having finished off the ones easy to reach, they were balancing and stretching at the end of branches to get at the remaining ones. The individual on the top shot had spent some time trying to reach a bunch of seeds beneath it. It then flew to the branch underneath and stretched its neck in the hope of being able to get them from there.

Happy feet

A mild day, the ground waterlogged with the past rains, and the grass peppered of earthworm casts, Lumbricus terrestris. A pair of Herring Gulls hunt for worms on the wet soil, rapidly patting it with their feet. The rapid rhythmic pattering creates vibrations on the soil similar to rain, and the earthworms move to the surface. I took a poor quality video, although it shows the behaviour of one of them, looking very intently to the ground and pecking occasionally. During some seconds it uses only one of its legs while keeping balance with the other.

Coot portrait

This coot called my attention due to the large size of the frontal shield. She came quite close to the shore in a local park and I was able to take her portrait.

Winter Herring gull pair

The Herring Gull pair at The Rock faithfully return to the park for the winter, and watch developments from their vantage point. I assume it is always the same pair, they stay together and I've never seen more than two at once. Herring Gulls are monogamous, mate for life and live long lives, so the pair might have been visiting the park for years. They are relaxed around people, and, unlike their relatives at the coastal resorts, do not bother people for scraps. They just wait. They know people will bring food to them at the park, no need to beg, just wait patiently.
 Herring gulls are in their winter plumage now, their heads and necks streaked with grey feathers. By February, their head and feathers will be pure white and soon after they won't be as regular in the park, having moved to their summer grounds for breeding.

Crows on ice

After days of heavy rains, it has been quite cold the last few days, and the large puddles everywhere have frozen over. A group of a dozen Carrion Crows had gathered this afternoon on the grass of my local park, probably before flying to their roost. This pair of Carrion Crows, undeterred by the cold, was actually foraging on an iced up puddle. One of the individuals even dared to walk on the ice, not bothered by slipping on it occasionally, an experience that is probably quite unusual, as they do not normally wade. This individual must have overcome a natural inhibition to walk on water. But not only that, both exploited this ability to look through the ice in search of food tidbits which normally would be out of reach, far from the puddle edge. The crows used their beak as a hammer to break through the ice and reach underneath, or to lift pieces of it. The less adventurous individual did this from the safety of the shore, but the other one walked about checking the whole surface of the puddle. Many ground-living invertebrates, such as earthworms, might have drown in the flooded ground after surfacing in search of air, and the ice itself provided the crow with a platform from which to obtain these otherwise unreachable resources.
 Another illustration of the wonderful opportunistic behaviour of crows.
 The following video has a short clip of the pair of Crows on ice. There is another one in my YouTube channel.

Communal bathing

Yawning is known to be contagious in primates, but having a good bath is something birds often will do in company. As soon as one starts, others nearby, often of the same species, will copy. Bathing washes and cleans feathers, and afterwards, the bird dries up by shaking tail, wings, body and head and then proceeds to oils the feathers by spreading over them a secretion produced by a gland above its tail. A few days ago, I watched these Mallards bathing and preening in sequence with some enthusiasm, today it was some Great Black Backed Gulls, the Sparrows in my garden often do it as well.
Male Mallards have good reason to keep their feathers in top condition, as they will be already paired or looking for a partner at this time of year. Maybe bathing is also an opportunity for showing off.

Bottoms up!

This is probably one of the most familiar duck behaviours. Mallards often 'upend' to feed, submerging the anterior parts of their bodies and keeping their tails pointing up, while keeping their balance paddling with their feet -  a behaviour most kids find hilarious. Although it is not a universal duck feeding method, Mallards are amongst the experts. Mallards are dabbling ducks, they obtain most of their food from near the surface. Upending allows them to reach just a little bit deeper and feed at depths not used by smaller dabbling ducks but too shallow for diving ducks. In contrast to smaller dabbling ducks, mallards and other large dabbling ducks can afford to upend as their large size allows them to reach deeper and to remain submerged for longer.

Proportion of Mallards feeding using different feeding methods (from Green, 1998).

In a comparative study of duck feeding behaviour, Andy Green found out that neck dipping and upending were the predominant feeding methods in Mallards. Ferruginous ducks, a species of diving duck, did not upend and barely used the neck dip, diving was overwhelmingly the most commonly used method. 

 You can watch Mallards upending in this short video:

More information

Andy J. Green (1998). Comparative feeding behaviour and niche organisation in a Mediterranean duck community Canadian Journal of Zoology, 76, 500-507 : 10.1139/z97-221

Greylag portrait

I took this photo last monday in a local park. I can't stop myself photographing Greylags, definitely a top bird for me, and I feel lucky that these geese are so approachable, most if not all of them of feral origin. The flock was watchful for dogs, and took off shortly after, but this handsome individual looked straight to the camera while posing nicely.

The Common Pochard

Common Pochards, Aythya ferina, are common wintering ducks in the UK. I find intriguing that most of the birds in my local park are males. However, this is the case for the whole UK winter population, with males outnumbering females in a 2:1 ratio. In sites where supplementary food is given this biased sex ratio can be much more extreme (5:1). Females appear to migrate further south than males, and the reason for this could be that males are much more aggressive towards females than they are to other males. Confronted with this intraspecific competition, females move on to areas where there are fewer males. Males might benefit from shorter migration distances by coming back earlier than females to establish breeding territories.

  Pochards, unlike other birds, seem to have the same pattern of activity between day and night, they are cathemeral. Bouts of feeding are followed by bouts of sleeping day and night, and they are often found resting in flocks during the day (they still sleep about 50% of the time).

  In the winter, these diving ducks feed mostly on seeds and fuiting bodies of aquatic plants (Chara, Nitella, and Potamogeton being a large fraction of their diet). Their distribution is limited by their diet, as they require large bodies of water with good population of aquatic plants. They feed by diving and up-ending, and, they probably rely on the sense of touch to feed, which may explain they do not need light to feed.

One of the few photos I have got of a female Pochard, in the company of Tufted ducks.

Carrion crows dunk their toast

I had the chance of watching a Carrion Crow dipping bread in a puddle this morning. The crow deliberately walked towards me holding a piece of bread in its bill as it approached the water. It was obviously so preoccupied with the task that took no notice of me taking the camera clumsily from inside my backpack. I stayed still and avoided eye contact while the crow carefully placed the bread on the edge of the puddle and nibbled a few bits. Immediately after, it decided to walk around the puddle turning a few leaves and stones over - even a leaf that was, literally, almost touching my feet. After this, the crow run to the bread across the puddle and ate it. You can see its gular pouch filling and there is little bread left on the photo above taken at the end of the following video.

I had previously seen just once this bread-dipping behaviour. While feeding the birds in the park with my daughter, the pigeons kept stuffing themselves on the bread. The whole chunks of bread inside the pigeons crops made their necks stick out funnily. A crow turned up, fetched some bread and then walked towards the pond edge, dipping the bread and eating it while wet and soft. Today's crow was more interesting, as it waited for a while before returning to the bread, as if allowing it to soften.

  Crows are amongst the few animals able to learn to wait to receive a reward. Dunking bread is equivalent to cooking: there is some food preparation involving costs: time, effort and potential food loss (another crow might come while you wait and steal your food) before you can enjoy an easier to eat food. Overcoming the impulse to eat the raw food straight away is a prerequisite for cooking. Young children are incapable of the self-control involved in having to wait for a reward - they are naturally impatient - and the ability develops slowly, but great apes are also able to control an impulse to eat a reward in exchange of delayed rewards of higher quantity or quality. Crows join humans and great apes in being able to delay gratification. Crows might be predisposed to waiting for a reward as they do routinely hoard food for later - leaner - times. Valerie Dufour and colleagues carried out experiments on captive Carrion Crows and Ravens that demonstrated delayed gratification. They showed the crow a desirable item (grapes, cheese or sausage) but gave them a less desirable food (bread). Then, if the crow waited for a length of time and returned the bread, they were given the tasty reward. The crows - at least some of them - were able to wait up to five minutes to exchange the bread to obtain the desirable reward. They were also more willing to wait longer for their favourite item (usually sausage).

Figure 1. General capacity to wait: percentage of successful exchanges according to the length of waiting period for individual Carrion Crows (from Dufour et al 2011).

  In the video sequence above, the crow carries out a series of activities before eating it (drink water, lift a few leaves and turn stones). This is reminiscent of displacement activities to alleviate a frustration. The experimental Carrion Crows, especially those waiting for longer, also carried out such displacement activities while waiting for the desirable reward (placing the bread on the ground, pacing up and down their cages, or hiding it repeatedly)(you can watch some videos of the experiments here).

More information

Dufour, V., Wascher, C., Braun, A., Miller, R., & Bugnyar, T. (2011). Corvids can decide if a future exchange is worth waiting for Biology Letters, 8 (2), 201-204 DOI: 10.1098/rsbl.2011.0726

Wandering Waxwings

I have litte interest in watching birds swept away from their native grounds by a tropical storm, or inexplicably lost and found far away from their usual migratory routes. Waxwings are different, and I have been wanting to see them for years. They might be rare, or not present in great numbers every year, but the UK is part of their distribution range. The last couple of days, I have been popping in a local supermarket carpark to watch a large flock of these amazing birds. Bohemian Waxwings, Bombycilla garrulus, as other boreal bird species - like Crosbills, Siskins and Redpolls - do not fit into a regular migratory pattern, they are instead irruptive migrants. It is thought that the species common name, Bohemian, comes from these wandering habits. In irruption years, many thousands of individuals flock and wander well south of their summer grounds in the the Russian and northern Scandinavian taiga making it to the UK. Flocks then move nomadically in search of food, as it is not cold winters what prompts their movement, but unpredictable food resources. Irruption years in Waxwings correlate with poor crops on fruit and berries in their northern grounds following a good fruiting year. Waxwings are highly frugivorous birds, their exclusive diet in the winter consists of berries and fruits: Rowan, Hawthorn, Cotoneaster, Mistletoe, Rose Hips and many others both wild and cultivated. The main resource, Rowan berries, fluctuates erratically across years in their summer grounds, as Rowan is a masting species, as fruit production is synchronised in the population and totally fails some years. During these poor fruit years, Waxwings initiate their movements earlier in the year, and therefore earlier arrivals of waxwings indicate that it will be an irruption year.
 During irruptions, waxwings carry on moving through the winter as they deplete their food resources locally, and they are wanderers all year round, with little chance that they will return to the same areas where they were born in the following summer. This winter is going to be one of those irruption years, and the Waxwing invasion is well underway.
 Waxwings are surprisingly small birds, similar in size to Starlings, to which they also resemble in flight, as they flock and have pointy, triangular wings. At close range there is no mistaking them, with their soft plumage, characteristic crest and 'zorro' mask. At even closer range, you might get to see the striking bright scarlet waxy drops and yellow streaks adorning their wings. They do look smart.
 As most fruit eaters, Waxwings need to eat a large number of berries to survive - an estimation was double their body weight in berries. A flock can quickly strip down a tree. When not feeding, they like to sit atop trees, preening and just looking around, while constantly chattering, a pleasing cricket-like and jingly call.

A large flock of Waxwings resting and preening.

The top of this Rowan has already been stripped, but there are still plenty of berries at the bottom of the tree, which are harder to reach 

A circling flock of Waxwings deciding where to stop

 These three were looking up nervously, might well have been keeping an eye on the Sparrowhawk soaring above them.

The flock I was watching was resting on a Rowan tree and the birds were not quite daring to do to the bottom of the tree to start eating. They increased the rhythm of they calls like they were agreeing on something, and took to the wing. I am so pleased I finally managed to catch up with them. Bon voyage!

More information

Barbara and David Snow (1988) Birds and Berries. T & AD Poyser. 268 pp.

Ian Newton (2006) Advances in the study of irruptive migration. Ardea 94, 433-460.

Koenig, W., & Knops, J. (2001). Seed-crop size and eruptions of North American boreal seed-eating birds Journal of Animal Ecology, 70 (4), 609-620 DOI: 10.1046/j.1365-2656.2001.00516.x

Food hoarding Coal Tits

One of the things I enjoy the most about watching birds is that even familiar species often surprise me with behaviour I have not seen before. I watched birds feeding on seed and peanut feeders a few days ago. A pair of Coal Tits, Periparus ater, showed their usual energetic prowess: a constant back and forth between the feeders, quickly snatching a seed and then flying away, to return within a few seconds later for another one. This time though, I could see where the Coal Tits were going and they were not flying away from the feeder to eat their seed in solitude, without the hassle of the larger birds, instead, they were storing the seeds: on the ground, pushing the seed into the soil, in the cracks in the pavement, on branches, in a conifer bush or in pots.
 Although corvids are more widely known to store food, food storing is common in Tits (parids). Marsh, Willow and Crested Tits are regular food storers, (although Great and Blue Tits are not). Parids store insects and other invertebrates (after decapitating them), seeds and nuts. They might store hundreds to thousands of items per day, using a different hiding place per item and even covering the hidden item with a piece of bark or stone. They might store the items a short distance away from where they were found, or up to 100 m away. They may often retrieve the food after a few days, but possibly much longer as not readily available food items (such as caterpillars) are often seen consumed by tits in the winter. A Japanese species, the Varied Tit, can feed its nestlings up to 5% of stored seeds from the previous summer-autumn. Parids display good memory not only spatial, to go to the exact place where the food was stored, but also to remember which caches have already been retrieved. Food storing in such small birds might contribute to survival when food is strongly seasonal or unpredictable and it can be retrieved when its consumption will make the largest contribution to survival.
 I managed a very short clip of a Coal Tit storing a seed.


But I wasn't the only one watching. This blue tit was also very interested in the Coal Tits.

After watching it, the Blue Tit came right up to a Coal Tit about to hide a seed - it is just visible in its beak in the photo below. After a brief hesitation, the Coal Tit decided to go somewhere else and left just after I took the following shot. Sorry about picture quality today, but all the shots were taken through glass.

More information
David F Sherry (1989). Food storing in the Paridae Wilson Bulletin, 101 (2), 289-304

Guarding the berries

The rowan in the garden is laden with succulent berries. Blackbirds have been showing an interest in the rowan since the beginning of the month. On the 9th, a male tried them, picking them up, and dropping them. It have me the impression it was checking how ripe they were, and he just felt they weren't quite right. Since them, I have flushed the blackbirds from the rowan a few times, often a pair. I watched a male feeding on honesuckle berries yesterday, while the cotoneaster does not seem to be ripe yet. This distinctive male - note the pair of white feathers on his chest - sat on the rowan for a while, surrounded by the colourful changing leaves of the tree and the clumps of heavy berries. Typical blackbird 'sitting' behaviour, quietly guarding his sweet red crop.

Cooperative breeding moorhens

I dealt with the topic of cooperative breeding in Moorhens in a post before, but I hadn't got photos illustrating the behaviour. In Moorhens, young from the first brood of the year will often stay around and help rear the second - or third - batch, and this is more likely to happen in good quality territories. Moorhen chicks are very mobile, but they still rely on their parents, and helpers, for food. Yesterday, in a visit to a local farm, we had the chance to observe the behaviour up close. There were three moorhen chicks, two adults and a subadult individual in the carp pond. We noticed that the moorhens were very interested in fish food, so we ended up feeding the moorhens. One of the adults picked up pellets in its beak, up to three at a time and passed them to the immature, the immature fed on them, but it would also carry the food to the chicks. Instead of the adult feeding the chicks directly, the subadult was an intermediary, ferrying the food from parent to chicks.

 Given their liking for fish food and the presence of visitors feeding the fish during the breeding season in the farm, this appears to be a prime moorhen territory. The Moorhens are also very used to people and are very confiding.

The carp at the pond

Little chicks on the shore

Adult - right - with following chicks and subadult, left

The adult with food pellets

The adult passes the food to the subadult

The subadult feeds the chicks

Some chicks beg the adult for food

Growing shiny feathers

I watched a family of crows with two young a few days ago. One of the youngsters appeared to be having a 'nap' on the ground. I have only seen feral pigeons do this before, never in crows, so I took a shot. The crow immediately became nervous and started moving away, following another one. When checking the photo, I noticed that a few brand new, glossy black primary feathers can be told apart from the worn, dark brow, immature ones.

Watch and learn

I watched a pair of Carrion Crows with a juvenile today. From a distance, you would say adults and young look the same, but young ones appear smaller than the adults, have a thinner bill, and lack the purplish-blue sheen of the adults feathers, with an overall impression of a dull, dark brown bird. The young one today followed one of the adults carefully, watching his every move, often having to trot to keep pace - even if the adult seem to walk normally. If the adult appeared to find a morsel, the young one begged, bill open and wings flapping. Crows being such adaptable birds, the young ones have lots to learn on how to find food. About three months after fledging, the young crows will become independent.

Blackbird cleaning slug

In the last month, I have observed four blackbirds eating large slugs. They spend a long time wiping them from side to side on the ground and then, as the one in the photo, cut them in smaller pieces - possibly to feed nestlings. I was alerted to the presence of this one in my garden by my cat, and I had time to snap a single shot before the blackbird picked up the slug and flew away.

Mute swan colour polymorphism

 After weeks of waiting for the cygnets to hatch, we were rewarded today by the mute swan family approaching us in a local lake. I noticed the two cygnets were different, one had grey-brown down and black beak and legs.

The other, had creamy white down, with pinkish-grey beak and legs.

It was quite noticeable when they were together.

 Next up a close up of the male, I even used the macro setting, that close we were. He was very relaxed around us, but he reacted by opening his wings, raising his neck feathers and hissing loudly when a dog approached the family. Both parents were incredibly protective of their cygnets, chasing away ducks, moorhens and even fluffy ducklings!

 The swan family, on the right, the female, which has pale feet.

The white cygnet illustrates the fact that Mute Swans (Cygnus olor) have a colour form called 'immutabilis', or unchanging, and also known as Polish swan. The mutation is sex-linked and recessive, and occurs in a gene located in the Z sex chromosome. Unlike most mammals, female birds have two different sex chromosomes (ZW), while males have two of the same kind (ZZ). If the female has the mutation, she will be white as a cygnet and will moult into an adult white plumage directly. A male needs to have two mutated forms of the gene to be a Polish swan. 'Immutabilis' adults are hard to tell apart when they are in the water, as the only trait that is different is the colour of the feet, which is paler. The immutabilis form is rarer in populations than the normal form, and it is more common in female swans.

 Other than the 'cute factor' when cygnets, the immutabilis form carries advantages and disadvantages for swans. Swans are very territorial, and they react aggressively toward white.  As they start moulting into their white feathers while being in their parents territory, the adults may start behaving aggressively towards the immutabilis cygnets. This means that young immutabilis flegdlings could be expelled from the territory earlier and may suffer highest mortality, as they need to venture and find a territory of their own when too young. Swans do not usually breed until their 4th year of life, so moulting into a brown subadult plumage pattern advertises to other swans, including their parents, that they are not ready to breed. On the other hand, if population densities are low, it could be advantageous to moult straight into an adult plumage and breed earlier.

Conover and coworkers studied the feral swan population in the East of the USA for nine years to establish the survival of cygnets of both morphs and the age at which they first reproduced. They ringed and neck banded young swans in two populations and follow their fate by thousands of resightings. Their results were striking: immutabilis cygnets (which they called AP, or adult plumage) had significantly lower survival rates from hatching to fledgling (73%) than grey cygnets (which they called SAP, or subadult plumage) (87%). This effect was mostly due to the higher mortality of male immutabilis cygnets, and mortality seemed to occur between August and fledgling, when cygnets grow their flight feathers. They stated:

We watched the parents of eight broods, which contained both SAP and AP phenotypes (four in the Chesapeake Bay and four in Long Island Sound), attack and drive out of their territories their AP offspring during August or September, while continuing to care for their SAP cygnets for several more months. We were able to keep track of eight of these ostracized AP cygnets; four of them perished within a month.

But all is not lost for the immutabilis swans. Although males suffered a higher mortality, the survivors were able to breed earlier than SAP males: by age 3, all of the surviving immutabilis males had bred, while just over 30% of the SAP males had done so. In the studied populations, the frequency of the immutabilis form does not seem to be changing, so the persistence of the immutabilis form could be reflecting a balance between the costs of being expelled early from the parental territory and the benefits of early breeding.

More information

Conover MR, Reese JG, & Brown AD (2000). Costs and Benefits of Subadult Plumage in Mute Swans: Testing Hypotheses for the Evolution of Delayed Plumage Maturation. The American Naturalist, 156 (2), 193-200 PMID: 10856201

Munro, R. E.,, L. T. Smith,, & J. J. Kupa (1968). The genetic basis of color differences observed in the Mute Swan (Cygnus olor) Auk, 85, 504-505

UPDATE 23/0/2022. I'm reading 'The Swans' edited by Sir Peter Scott, and he discusses the possible force behind this colour polymorphism, which appears to incur in the cost for cygnets that they suffer more aggression from parents and are expelled from home territories at an early age: hunting pressure. Young swans were preferred as food as they were more tender, and therefore the immutabilis variety were hunbted less, as they were thought as adults.

Urban Kittiwakes

Some urban birds used to be cliff nesters before towns and cities existed: House Martins and Swallows, Swifts, Barn Owls, and some seagulls. Kittiwakes are birds of the open seas. They do not use rubbish tips to feed, like other gulls, and they are only brought inland when gales or storms push them out of their preferred habitat. They only come to land to breed and cliffs are great magnets for them: they will perch their nests made of grass, mud and seaweed in small ledges. In the cliffs where they nest their constant calls contribute to create a wonderful atmosphere in the breeding season. 

Buildings on seaside towns offer them artificial cliffs, safe from predators. We watched the large Kittiwake colony in Scarborough. Some nest in luxury, single occupation ridges on the ornate walls of the Grand Hotel. 

Others cram in apartment buildings, having to share their window ledges with two other pairs. These were making such a rattle I couldn't imagine the human occupants of the building would get much sleep.

The lower kittiwake classes have to content themselves with a nest under the bridge. One adult fed little fish to the adult on the nest in the middle.