Individual human recognition in crows

Corvid researchers have ample anecdotal evidence that crows recognise individual humans: crows are unusually alert and often direct mobbing calls to researchers that have previously ringed them, while ignoring other researchers. Other crows follow and harass individuals who feed them in order to obtain food, something that Ralph Hancock has described to me in comments to this blog (see previous post), and amply illustrated in his blog (Charley and Melissa are the pair of crows that often pester him for food). Unlike predators, who tend to be dangerous in general, people can be either very dangerous, mildly dangerous, neutral or good to crows. Some people, e.g. farmers who treat them as pests persecute and kill crows (see photo below) and crows might learn to be cautious when they see them and fly away before being shot. Other people are plain annoying, as bird ringers who trap them, and it may pay to learn who they are so that the trap is avoided next time. Yet others people are good to crows, such as people who feed them, and it may pay to be confiding and even harass them to get more food. It is not surprising that intelligent birds like crows pay attention and learn to discriminate between 'good' 'neutral' and 'bad' people and act accordingly.

Two Carrion Crow carcasses on the cows feeder of a local farm.

 John Marzluff, a researcher at the University of Washington has studied crows for many years, and part of his research has involved trapping and ringing crows in Seattle. Marzluff was aware of the crow's mobbing behaviour towards the specific researchers that had trapped and ringed them but he wanted formal proof. He incorporated ringing into an experiment to test if crows recognise individual humans. He worked with American crows, Corvus brachyrhynchos, a close relative of the Carrion Crow with a similar social organisation. The research included urban populations that included previously trapped and ringed individuals, and also 'naive' populations that had not been ringed before. Experiments included a single negative event: the setting a trap (a net launcher) to capture feeding crows in 5 different sites. The people activating the trap, capturing and ringing the birds wore specific masks and/or hats (a 'dangerous' mask). Masks were used so that they were interchangeable and effects due to inadvertent researcher behaviour, outfit or body size could be removed. During transects around the crow territories, researchers (wearing either the dangerous mask or a 'neutral' mask) assessed crow activity towards them before and after the trapping event. They in particular noted if crows displayed the 'scolding' response to them (defined as a harsh, alarm ‘kaw’ directed repeatedly at the observer, and accompanied by agitated wing and tail flicking) or were indifferent. The experiments were repeated by people unaware of the experimental design or objectives, which were asked to walk around the crows territories wearing or not the mask used during the trapping event or a different, neutral masks. This experiment removed any subjective bias by the experimenters themselves.
 The experiments show that crows rapidly learn to recognise the 'dangerous mask' used during the trapping in their local site, with more scolding in response to the dangerous mask than to neutral mask during and after the trapping event, but no differences before the trapping event. In addition, the percentage of local crows scolding the person wearing the dangerous mask increases from 26% steadily with time over 2.7 years to 66%, suggesting that the local crows learn from each other about the dangerous person. The masks used in one of the experiments were of ordinary people and the crows learned to mob the specific mask associated to the trapping and not similar masks.

The crows today calling and wing-flicking.

  Today I walked around the park today with my camera. Three crows at the end of the park, in the same area where they mobbed and followed me three weeks ago immediately flew to the top of a tree and cawed harshly looking in my direction, wing-flicking, then one of them flew towards the tree by which I was standing. I took a video that shows how it is scolding me and records the call. The top shot is a screen gan of the video. As I left the park they stopped cawing. I seem to have become the not so good people to the local crows, maybe I will wear a mask next time.

Cawing 

And flying towards me

More information
Marzluff, J. M., Walls, J., Cornell, H. N., Withey, J. C. and Craig, D. P. Lasting Recognition of Threatening People by Wild American Crows. 699–707 (2009).

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.

The Viking gulls

A flock of about 100 common gulls winters in the park, they arrive at the end of September/October and are around most of the time until the end of March. They are very excitable and their squeals provide the background noise of the park in winter, especially when visitors empty their bags of bread by the side of the pond. A cacophony of calls and chases ensues while the gulls pick the bounty fast, before the ducks and geese have the chance to react.
 Is not only bread though for the park gulls, there are very quiet times, especially during the middle of the week, and the gulls will move onto the grass, looking for worms and other invertebrates, watching the ground intently as they walk.

 In wet days they can be seen 'dancing' (foot-paddling) to entice the worm to the surface of the soil. Like so.

Then they spend some time just flying in circles over the park, in a flock, I am not sure if in preparation to roost, although I am not sure where they spend the night.

A quiet moment in the flock, with preening, snoozing and yawning by the pond.

This is an adult one on winter plumage. Note the yellow bill with faint dark ring near the tip and the yellow legs, and spotty head.

on the 3rd of February this adult looked very nice on the snow, still in winter plumage.

On the 20th of February this adult had an almost white head and a thin red eye ring.

A close up of an adult's head showing mainly yellow bill, red ring. Note the scruffy back of the head, showing the ongoing moult towards a completely white head plumage.

I find them endlessly fascinating and can't stop myself from photographing them, and they are often co-operative, as they are so used to people. When I noted that the flock disappeared each year, one day in March or April I wondered where they would go in the summer, to breed. I need wonder no longer, these gulls come from Bergen, in Norway.
While watching them one day in January I found a couple of Common Gulls with plastic colour rings. I spent some time looking at the legs of many gulls since that day, but I didn't spot any other ringed ones. I managed to get photos where I could read the code and submitted the samples to Euring. I got an e-mail the same day from Morten Helberg with details of their ringing and recoveries. Since then, I have seen the ringed gulls a few times, and managed to get their portraits.

This is J2EX, sex unknown ringed its first autumn (1st calendar year in 2013) which means now should be in its 3rd calendar year (almost adult), although the bill and legs are still grey/bluish and doesn't have a red eye ring or prominent wing 'mirrors'. This is its ringing/recovery history:

15.09 2013 Byparken, Bergen, Hordaland, Norway
17.09 2013 Tveitevannet, Bergen, Hordaland, Norway
20.09 2013 Tveitevannet, Bergen, Hordaland, Norway
21.09 2013 Byparken, Bergen, Hordaland, Norway
14.06 2014 Kilnsea, Humberside, Great Britain
14.01 2015 Pearson park Hull, Humberside, Great Britain (the photo above is from yesterday, also observed 22/01/2015)

This is JV47, Sex male age, 1 cy when ringed last October, so it's in his first winter. He still called like a gull chick when feeding, and adopted this hunched chick posture. Legs and bill base pinkish.

This is it's ringing/recovering history:
05.10 2014 Tveitevannet, Bergen, Hordaland, Norway
(in the month after it was ringed the flock came back to Pearson Park)
14.01 2015 Pearson park Hull, Humberside, Great Britain 

Looking at photos yesterday, I found another ringed common gull, from the 20th of February. It looks like a first winter bird. The code reads JR20. I will update the post when I hear back from Euring.

It is very nice to know where these gulls spend the summer, but something equally rewarding is to know them as individuals. The rings have allowed me to recognised them in my visits to the park. I will look forward to them coming back in years to come, as gulls can be long lived. A typical Common Gull lives for 10 years (the record is 27).

Offspring recognition in Starlings

The first Starling fledglings joined their parents in the lawn of the park this morning, running behind their parents begging for food, with a cacophony of calls. Starlings are highly social birds, they like to feed together, so the chances are that the still dependent young will join unrelated young while still expecting to be fed by their parents. Furthermore, starlings in an area have synchronised egg laying so that many young will fledge on the same day. While the young are inside the nest, parents do not need to particularly recognise their offspring individually - they are likely to be their young. However, how can they make sure they recognise their offspring from others in the flock, so that they feed their own young after they fledge?
  Every year, a week or so before the fledglings leave the nest, adults start using a harsh call 'charr, charr!' (above, listen here) and the by then loud voices of the young can be heard replying from inside the nest. Why, I wondered, do they do this?
 Linda van Elsacker, Rianne Pinxten and Rudolf Frans Verheyen carried out experiments in nest box starling colonies in Antwerp (Belgium), either swapping broods of different ages for a day (Exchange experiment), or offering a choice between their chicks and alien chicks in nearby nests (Choice experiment), or swapping the nest by an empty one and relocating their nest containing young at a certain distance (Search experiment) at different chick ages.
In their choice experiments, carried out when young were 5, 11 and 16 days old, they showed that parents accepted and fed strange chicks until they were 16 days old, as shown by the weight gain of the chicks. In contrast, most parents were able to recognise their chicks when they reached 19 days, ignoring the strange ones completely, and this behaviour was found in all parents when chicks were 20 days old. So by this age adults were able to recognise their chicks.
In the search experiments they showed that the ability of parents to locate their offspring improves quickly and by the time chicks reach fledging age (20-22 days old) 97% of parents searched for and relocated the moved nest containing their young within an hour of the nest having been moved.
 The constant calling by parents and offspring in the days before fledgling might be a way of reinforcing this recognition. So, by the time the offspring are ready to fledge, and then mingle with other chicks, parents are able to recognise their offspring, presumably by their calls.

More information

Frans Verheyen, R., Van Elsacker, L., & Pinxten, R. (1988). Timing of Offspring Recognition in Adult Starlings. Behaviour, 107 (1), 122-130 DOI: 10.1163/156853988X00232

Chaiken, Marthaleah (1992) Individual recognition of nestling distress screams by European starlings (Sturnus vulgaris). Behaviour : 139-150.

Young starling looking for food this morning

...and chasing its parent begging.