The hybrid goose in the park

I have known this goose since 2005. It is a hybrid between Canada Goose and possibly Greylag, and it turns up every winter in my local park. Today, it behaved gallantly, chasing away other geese and ducks while its partner, a Canada goose, fed.

The hybrid goose holds the pair of Canada away from the food source, allowing his partner to feed unmolested.

This goose is a large bird, with a mixture of features from both species (see photos of Greylag and Canada below), with the white patch on the face of the Canada, the pink legs of the Greylag and a beak half, black half pink.

A Canada goose

 A Greylag

 I think the hybrid is a male. He is paired with a female Canada and travels with a Canada flock. Hybridisation is a fascinating issue. In a puritanical view of species - which were created, would not change and could be nicely put into separate drawers - hybrids, were viewed as oddities: unnatural, often sterile, hard to put away in a neat drawer. This view has changed a lot lately. Recent genome sequencing data have shown that we humans seem to be a melange of different hominid isolates that mixed when they met; polar bears and brown bears have been shown to have often interbred during the Pleistocene; Carrion Crows and Hooded Crows do it; Willow Grouse and Rock Ptarmigan do it as well. There are many more examples. Natural climatic changes, such as during ice ages, often brings species together facilitating hybridization. Human introductions, placing species that previously didn't come together in the same areas can also promote hybridisation. Hybridisation is not only more frequent in nature than previously thought, but can also fuel species diversification and adaptation.
 Geese hybridisation is interesting as, when young, goslings undergo a phenomenon called imprinting. After hatching, goslings have a sensitive period during which they attach themselves socially to any moving stimulus, and follow it. This usually happen to be their parents, but they will eagerly follow people when goslings are hatced in an incubator. Even their mating preferences are determined to some point early in life, as goslings imprint on the adults that rear them - this is called sexual imprinting - and, when adults, will try and find a mate of the same species of the individuals that reared them. In nature, errors can happen. For example when individuals practice egg parasitism - laying eggs on another species' nest - or a brood from another species is adopted or brood amalgamation, when goslings from  different species pool together and the adults of one of the species take care of them.
 What happens to the fostered brood when they grow up? They imprint on their foster parents, which rear them as if they were their offspring, but they still look like their biological parents. Eric Fabricius carried out an experiment in the wild to examine the effects of sexual imprinting on hybridisation in geese. He swapped all eggs from two nests of Canada geese by Greylag eggs. The cross-fostered Greylags migrated with their Canada parents and upon returning to the breeding ground the following spring they paired up:

Of 35 returning birds, all 16 females paired with greylag goose males (100%) whereas of 19 males 5 paired with Canada goose females (14%) and the remaining 14 with greylag goose females (74%). The pair bonds generally persisted as long as both birds were present, but after loss of a partner, the remaining bird usually re-mated. Even when this happened several times during the lifetime of a male, the new mate was always a Canada goose female, showing that the males were sexually imprinted to this species. The Canada goose females which had mated with the greylag ganders also remated when widowed, but their new mate could be either a Canada goose or a greylag goose.

All cross-fostered females paired with Greylags. They looked like greylags, so they weren't courted by Canada males, just Greylag males. The pattern in the males is interesting, as they probably actively courted Canada females - and some accepted them-  but they were also found attractive by greylag females and they ended up pairing with them. Only the category of cross-fostered males pairing with Canada are likely to father hybrid offspring. What happens to the hybrid offspring is interesting as they do look intermediate between species. If is still unclear if hybrid CanadaxGreylags are fertile. The hybrid in the park then probably had a cross-fostered dad. He appears to have no trouble keeping a mate, and if he is always as considerate in his behaviour as today, she might as well keep him.

References
Fabricius, E. (2010). Interspecific Mate Choice Following Cross-fostering in a Mixed Colony of Greylag Geese (Anser anser) and Canada Geese (Branta canadensis). A Study on Development and Persistence of Species Preferences1 Ethology, 88 (4), 287-296 DOI: 10.1111/j.1439-0310.1991.tb00283.x


Edwards, C., Suchard, M., Lemey, P., Welch, J., Barnes, I., Fulton, T., Barnett, R., O'Connell, T., Coxon, P., Monaghan, N., Valdiosera, C., Lorenzen, E., Willerslev, E., Baryshnikov, G., Rambaut, A., Thomas, M., Bradley, D., & Shapiro, B. (2011). Ancient Hybridization and an Irish Origin for the Modern Polar Bear Matriline Current Biology, 21 (15), 1251-1258 DOI: 10.1016/j.cub.2011.05.058


Quintela, M., Thulin, C., & Höglund, J. (2010). Detecting hybridization between willow grouse (Lagopus lagopus) and rock ptarmigan (L. muta) in Central Sweden through Bayesian admixture analyses and mtDNA screening Conservation Genetics, 11 (2), 557-569 DOI: 10.1007/s10592-009-0040-9

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.