City gulls

Most gulls breed away from towns and cities, in lakes, cliffs and other wild habitats. In the winter, however, several species undergo a regional migration toward human habitats, and come back in flocks to use the abundant resources we provide them: litter, refuse and bread. One of the most abundant is the Common Gull, Larus canus. Above, an individual in the pose at the end of giving a long call.

It is curious that gull species have different habitat preferences, even inside towns. Common gulls (all photos above) are abundant in the local parks and are often seen flying over busy streets, but they are rarely seen feeding there. They are very social, and often feed in large flocks on expanses of grass, often seen "worming", with a funny dance, or waking looking intently to the ground. They join ducks and pigeons to be fed with bread in my local park, where I took the photos above, and then they are very approachable. When at close quarters, they have a gentle face, with dark eyes and a rounded head, and greenish bill and legs. Although their heads are white in summer, they are lightly spotted in winter.

Caching carrion crow

Many species of the crow family store food when it is plentiful for future use in harder times, a behaviour called caching. Some species rely on stored food more or less all year round, but others might do it occasionally. Carrion crows, Corvus corone, in particular, hoard food when they find some discarded human food, or other, occasionally abundant supply of edible items such as acorns. Today, I was walking along a path when I noticed a carrion crow on the verge. Carrion crows around here are usually very wary of humans and expected it would fly away. It didn't. I stopped with my back to the crow, took my camera slowly out of my bag and took some photos. The crow (above) was indeed very preoccupied with a few pieces of food on its beak, putting them down carefully, covering one with leaves, and then moving a few steps and repeating the procedure with another piece. I have watched carrion crows caching food - including chocolate! - before. What happens to this stored food? Do crows remember where they stored it? are these valuable resources to turn into in times of hardship?
  R.K. Waite carried out observations of caching crows, rooks and magpies in fields near copses. The main items they cached was acorns, and this behaviour was most common in the autumn, although carrion crows also cached large earthworms when they were plentiful. The birds carried the items in their bill or in a pouch under the tongue and hammered the acorn in a hole they had pecked on the ground, covering it afterwards with leafs, tufts of grass, or soil. These corvids are scatter-hoarders, they do not use the same exact location every time, but the stored food was distributed in many sites, often on the fields away from the trees. By January, there were no acorns to be seen on the ground. It is unclear if Carrion Crows remember the exact location of each cached item, although this has been suggested for Rooks, but they might retain a memory of the general area. Waite found out two different retrieving behaviours. In the first type, individuals foraging in the field for invertebrates came across a cached item, apparently, just by chance, and ate it, they carried out looking for invertebrates afterwards. In the second type of behaviour individuals appeared to be actively searching for cached items during winter:

On 14 occasions in late winter, flocks of Rooks or pairs of Carrion Crows or Magpies were seen to recover cached acorns in a quite different way. First, acorns were found about 10 times more quickly. Most observations were of birds foraging on fields rarely used at other times, while some birds found more than one acorn during a foraging bout and only eight out of 56 birds took any invertebrates. Second, searching occurred on days when temperatures were significantly below average and invertebrate availability was reduced

Waite's analysis shows that recovering cached items is a profitable way of foraging. The time spend storing the food should the taking into account as a cost, but as this happens where there is not a lot of competition, the nesting season is over, and there is a surplus of food, this cost is offset by the benefits of retrieving the food in cold days when foraging for earthworms and other invertebrates is not very profitable. Waite wondered if Rooks, Carrion crows and Magpies acorn caching behaviour might make them inadvertent, but better foresters than the Jay, as inevitably, some acorns will be forgotten or just not needed and will germinate in the spring in the fields, away from established woodland.

More information
Waite, R. (1985). Food caching and recovery by farmland corvids Bird Study, 32 (1), 45-49 DOI: 10.1080/00063658509476854

Great Tit nestlings respond adaptively to different antipredator alarm calls

Young birds are vulnerable. While they are still in the nest they can easily fall prey to cats, snakes or predatory birds, and once they leave it they are still naive and clumsy and they can also be easy prey. Parents, however, can help: they are experienced and know what other animals represent a risk, and they could make a difference by communicating this to their young offspring by using alarm calls. In a recent paper Toshitaka Suzuki showed how Great Tits (above, a fledgling) produce different alarm calls depending of which predator approaches their nest, and how, crucially, nestlings use this information to behave in the most effective way to avoid predation. The main predators for Great Tits in Japan are the Japanese Rat Snake species and the Jungle Crow. Snakes fit into the cavities Great Tits use and can then kill the chicks, while crows can only snatch chicks approaching the nest entrance. Suzuki presented nesting Great Tits with either a stuffed jungle crow (11 nests) or a live snake (10 nests) in a transparent plastic box, and the parents readily responded to the predators with repeated alarm calls.

In response to a crow, they continually gave ‘chicka’ alarm calls that were composed of several different types of syllables, but these calls were rarely produced in the snake trials. Instead, when detecting a snake, parents produced ‘jar’ alarm calls that were composed of harsh syllables. Such ‘jar’ alarm calls were repeatedly given in response to the snake, but were never uttered for the crow.

He recorded the nestlings responses to the parents' alarm call using video cameras set inside the nest. When the nestlings heard the 'chicka' call, they crouched inside the nest, making less likely that a crow would be able to reach them from the entrance hole. In contrast, upon hearing the 'jar' call, all nestlings in the 10 nests tested with the snake jumped hurriedly out of the nest. Snakes can easily enter the nest, so early fledgling is the only chance of escape. The parents took care of the early fledged nestlings as normal for fledglings. Although early fledgling can mean lower chances of survival, it is a better option to an almost certain death when a snake enters the nest.

This study shows that parent offspring communication can be quite nuanced, and hints at how little we still understand important aspects of the behaviour of common bird species.

References
Suzuki TN (2011). Parental alarm calls warn nestlings about different predatory threats. Current biology : CB, 21 (1) PMID: 21215927

Woodpigeons and Holly

 There is a mature holly on a street in my way to work. It's leaves don't have any thorns and it is a very lush female specimen. A few weeks ago it was an impressive sight, laden with bright berries. All through October and November, it has been visited by Woodpigeons, balancing precariously and gorging themselves on the berries.

Planes and goldfinches

This morning coming into work I heard the unmistakable chirps of squabbling goldfinches. There was a large flock feeding on a line of plane trees. While I climbed the stairs I thought delightedly that the window in our lab overlooks the trees, so I could have a level view of the feeding goldfinches. There they were, hanging from the bauble-like seed balls or balancing from the thin stems holding them. London plane trees (Platanus x acerifolia) is an important food resource for goldfinches, as it provides seeds during the autumn months into the winter. The photos didn't come brilliant - I blame the dirty windows - but I think the one on top captures the atmosphere of the feeding flock. I count seven, how many can you see?

More information

Sachslehner, L. M. (1998): The significance of Plane-trees Platanus x hispanica M. as a food resource for Goldfinches Carduelis carduelis L. in Vienna. Egretta 41: 90-101.

Beach Rooks

The last couple of times I've been at Hornsea beach I've been surprised by the gang - sounds more appropriate than the collective names of "building" or "clamor" - of rooks. They feel at ease cruising the beach up or down on the sand, gliding over the waves or over the promenade wall in search of morsels of food. They look like rooks that tried to be a seagull and they quite liked it. I love how incongruous they look with the blue backdrop of the sea, but also how the behaviour of this particular group of individuals illustrate how resourceful corvids are.

Eats shoots and leaves and buds and flowers

A woodpigeon feasting on cherry flowers. I have seen them in the last few weeks eating cotoneaster berries and poplar buds (or catkins, hard to say). Come May, they will take advantage of Horse Chestnut flowers too. The one below has stretched all she could to strip bare two inflorescences, they are quite tricky to reach, but woodpigeons are not scared to stretch their necks and almost hanging upside down to reach the best bits!

The bumblebee tit

Today I watched a pair of Blue Tits paying a lot of attention to the inflorescences of Mahonia in the local park, coming back to them again and again. What were they doing? If you hear nectar feeding in birds you would most likely think on hummingbirds and the tropics. However, several bird groups feed regularly on nectar in addition to hummingbirds, honeyeaters and sunbirds. In Australia, birds are actually the main flower pollinators. Although nectar feeding behaviour in Europe is far less widespread, it does happen. In 1985, Hugh Ford reviewed the handful of studies suggesting or indicating nectarivory in European birds (see table below).

 Most of the species were warblers, with the Chiffchaff and the Black-cap the most cited ones. Warblers winter in southern Europe or Africa, where there is a larger proportion of bird-pollinated flowers and where nectar feeding in birds, is more widespread. They are also known to exploit nectar while migrating, as a quick way to gain energy. The bird species that most commonly feeds on nectar in northern Europe, however, is - you guessed it - the versatile Blue Tit. Blue Tits seen on flowers are often thought to be foraging for insects, or feeding on parts of the plant, such as petals. However, Blue tits have been recorded feeding on a range of flowers, both introduced garden varieties and native ones: Gooseberries, Flowering currants, and the Fritillary Imperial Crown. What is more, Fitzpatrick, studying suburban blue tits, found that nectar can make a substantial part of Blue tit diet in early spring. Feeding on flowering currant inflorescences, Blue tits chose the most productive flowers, those with a darker pink rim. They used two strategies to get at the nectar: pecking the corolla out to reach the nectaries, or perforating a hole on the side of the flower - bumblebee style - to reach the nectar directly, as the flowers are too narrow for them to insert their beaks, and therefore cause quite a deal of flower destruction. Coal Tits were also observed feeding on the Flowering Currants, but they inserted their more slender beak into the flower and thus did not destroy the flower in the process of feeding.
   The Fritillary imperial crown is an impressive red or yellow flowered bulb in which a whorl of wide, flowers hang from a stout bare stem. It originates from Asia but is widely planted in the UK. Búrquez, showed that Blue tits not only collect nectar from these flowers, but they also act as are efficient pollinators of the plant.

  Blue tits in native habitats are often seen feeding on willow blossom, so nectar feeding seems to be another of the wide variety of opportunistic behaviours used by this tit to use resources.

More information
Ford, H. (1985). Nectarivory and Pollination by Birds in Southern Australia and Europe Oikos, 44 (1) DOI: 10.2307/3544053

Búrquez, A. (1989). Blue Tits, Parus caeruleus, as Pollinators of the Crown Imperial, Fritillaria imperialis, in Britain Oikos, 55 (3) DOI: 10.2307/3565592

Fitzpatrick, S. (1994). Nectar-feeding by suburban Blue Tits: contribution to the diet in spring Bird Study, 41 (2), 136-145 DOI: 10.1080/00063659409477210