Jays and acorns

A few weeks ago, on a local urban walk, I had the chance of watching some Jays collecting acorns from the oaks. It's been a good mast year and the veteran oaks at the cemetery were laden with acorns. Jays are a scarce and shy species in my city, but occasionally I come across them in the most wooded green spaces. These individuals, at least two, were collecting acorns, flying back and forth from the tree to their larder, a site out of sight beyond the road. Before disappearing into the foliage of the still green oak, they often paused on trees nearby, which is how I took the photo below, the wind pushing the Jay's crest up.

Caching behaviour

Jays are omnivorous and opportunistic in their food habits, but during autumn they become dedicated food hoarders. They are resident birds that depend on their stored harvest to survive the winter and early spring, and are acorn specialists. They have a pouch under their tongues and can carry up to nine acorns in a single trip, although in 80% of trips they will carry one or two. Their acorn reserves will be scattered, a single acorn buried in a shallow hole in the ground, around their home range, and the reserves will be steadily used. You might see Jays in small parties - often detected by their screeching calls -  but they tend to be mindful before they bury each acorn, away from the prying eyes and ears from other Jays, which will be all too happy to pilfer other individual's hoards. Experiments by Nicola Clayton's group have shown that their caching behaviour is dependent of potential pilferers being around and they will cache preferentially behind an opaque screen when other individual is watching, if they are within earshot of other individual, they will cache in quieter substrates (sand) rather than noisy gravel.

Oak foresters

Jays can store several thousand acorns per year, and rely on their spatial memory skills to retrieve them.  They have a mutualistic relationship with oaks, being crucial dispersers of acorns. As not all acorns will be consumed by jays, oak long-distance dispersal depends mainly on Jays, and the forgotten or unused acorns are perfectly planted to successfully germinate. The dispersal distance,estimated using radiotransmitters inserted in acorns provided to Jays in feeders in the landscape ranged from a few meters up to about half a km.

A Jay with an acorn it has just retrieved. It took about minute to find it. Watch the full clip here:

Complex cognitive abilities

It is striking that Jays manage to remember the location of thousands of caches. As other caching birds, they have excellent spatial memory, and perform very well in spatial memory tasks. Experiments have also shown they have episodic memory, an ability to recall specific events and details, both when caching and when pilfering. They might also prefer to cache near vertical structures, which might facilitate recall.

Jay with peanut. Jays are part of the bird community of towns and cities, particularly when tree cover and food resources (oaks or bird feeders) are available. 

More information

Kurek, P., Dobrowolska, D. and Wiatrowska, B., 2019. Dispersal distance and burial mode of acorns in Eurasian Jays Garrulus glandarius in European temperate forests. Acta Ornithologica, 53(2), pp.155-162.

Legg, E. W. & Clayton, N. S. Eurasian jays (Garrulus glandarius) conceal caches from onlookers. Anim. Cogn. 17, 1223–1226 (2014).

Madge, S. and G. M. Kirwan (2024). Eurasian Jay (Garrulus glandarius), version 3.0. In Birds of the World (B. K. Keeney, Editor). Cornell Lab of Ornithology, Ithaca, NY, USA. https://doi.org/10.2173/bow.eurjay1.03

Pons, J. & Pausas, J. G. Acorn dispersal estimated by radio-tracking. Oecologia 153, 903–911 (2007).

Shaw, R. C. & Clayton, N. S. Careful cachers and prying pilferers: Eurasian jays (Garrulus glandarius) limit auditory information available to competitors. Proc. Biol. Sci. 280, 20122238 (2013).   

Pied Wagtail winter territories

In the last few weeks, two Pied Wagtails have been feeding around the pond in my local park, staying near each other, but not too close, one chasing the other every now and then. I have watched this before, and managed to get photos last year (top shot, East Park, 9th January 2023). This behaviour, of two Pied Wagtails 'teaming up' to defend a territory during the winter, is quite typical of the species, and it was studied in detail in the early 1980s by Nick Davies and A.I. Houston along the river Thames near Oxford. The feeding territories studied were along the water, on both banks, where the wagtails pick small flies, spiders and beetles often washed onto the mud at the waterline, circuiting along one bank, then the other. The territory owner, usually an adult male, occasionally accepted an intruder as a 'satellite', often a female or juvenile, especially when there were enough resources to share. The satellite appeased the owner with a specific display, with bill and tail pointing up. The owners were more likely to tolerate the satellite when food was more abundant.

Appeasement posture of female White Wagtail (from Zahavi, 1971).

Although the presence of the satellite meant food resources needed to be shared in the territory, the satellite also helped with territory defence. The territories were defended vigorously, as the food resources depleted as the wagtails fed on the washed out insects, so intruders would reduce the feeding rate of the territory holders. Territory defence also involved calls, both of the intruding bird and of the residents. Davies and Houston quantified the benefits and costs of territory defence and accepting a satellite depending on the quantity of available resources.

It is clear that Pied Wagtails have a very flexible social behaviour. They gather in large, compact communal roosts during the night. Also, in places or at times where there is a glut of resources, for example during ploughing time, or emergence of insects, territory defence may break up and the wagtails might gather in loose flocks with little aggression.

In these photos of the East Park pair (above and top shot), the differences in plumage between the male (at the front) and the female behind are apparent.

I couldn't take a photo with both individuals from the 7th December at Pearson park together, but the difference in plumage indicates a male (above)...

... and a juvenile (below) is also clear. Note the juvenile's yellowish face.

More information

Davies, N. B. Food, Flocking and Territorial Behaviour of the Pied Wagtail (Motacilla alba yarrellii Gould) in Winter. J. Anim. Ecol. 45, 235–253 (1976).   

Zahavi, A. The social behavior of the White Wagtail Motacilla alba alba wintering in Israel. Ibis 113, 203–211 (2008).

Redpolls and Goldfinches feeding on Sycamore aphids

 I'm used to finding Lesser Redpolls in the coldest days of winter, when small groups feed quietly on birch catkins. Learning their cheerful 'chi-chip' call, sharper and less liquid than Greenfinches, has helped me detecting them as they move around the city. I was surprised to hear their flight calls amongst a flock of roving Goldfinches at my local cemetery, a misty but mild morning. I trained my binoculars high up on the Sycamores and spotted them, apparently gorging on the last fat sweet aphids still under the Sycamore leaves, together with the Goldfinches. Some Chaffinches and Blue and Great tits were also on the sycamores, but I'm more used to these species feeding on insects. The distance and the poor light didn't make for great photos, but I was pleased to record a behaviour I had never seen before for both Redpolls and Goldfinches.

Sycamore aphids.

Redpoll gleaning sycamore aphids.

Lesser Redpoll.

Lesser Redpoll.

Goldfinches and sycamore aphids.

A flock of local Lesser Redpolls

The coldest morning of the year so far, I take a walk around my patch. Lesser Redpolls are a rare winter visitor in the city, and it's hard to predict where to find them but my local patch has been quite reliable every year and cold weather pushes them south. Today I encountered a small flock quietly feeding on catkins in some small birches in the cemetery. There were at least five, one of them, a male. They allowed me to approach and watch them hanging from the thinnest branches, holding a birch catkin against the branch with a foot while feeding from it so that they can extract the seeds more efficiently.

Adult male Lesser Redpoll.

Here you can see how they hold catkins while they feed.

A female/immature feeding.

A view of the flock. From a distance, very hard to see!

They kept feeding, until a sudden Blackbird alarm flushed them all but one. The lone individual called, and left flying towards the flock.

Rooks hoarding acorns

It is a mast year, with a bumper crop of acorns across the city. October is peak acorn season and last week I saw the first Rooks carrying acorns. Acorns are packed with energy, and several bird species take advantage of them. Woodpigeons, presumably swallow them whole from the trees, but Rooks and Jays collect the harvest and store it for use during the winter. Both species are scatter hoarders, and cache individual acorns on the ground, and use their extraordinary spatial memory to recover them later in the year, when other food resources are scarce. Although the Jays are best known for this behaviour, Rooks are also amazing acorn hoarders. Rooks can transport acorns - and other food items - in a pouch under their tongue, which obviously bulges as they fly over with their pouch full. The number of acorns they can carry depends on the acorn size, and varies from 2 to 7. They prefer to cache the acorns on grass, and can fly up to 4 km from oaks to suitable grassland. Once they find a good spot, they drop all the acorns they are carrying and bury each one by one, by first making a hole in the ground with their bills, and then hammering the acorn in and covering it with grass, leaves or soil. Later on, they will visit the caching sites in the winter, find their stored acorns and crack them open to feed. 

A vocal Rook on an oak canopy, surrounded by plenty of acorns.

Rooks, unlike Jays, are very social and engage in communal acorn collecting, becoming very vocal when landing on the oaks canopy. They prefer to gather acorns with other Rooks, and individuals appear to join other individuals gathering acorns by flying in the opposite direction of individuals with full bills. When it comes to caching though, Rooks prefer to be alone, to avoid cleptoparasism, when other individuals try and steal their stored acorns.

Rooks displaying, the individual on the right, with distended sublingual pouch, passed an acorn to one on the left, presumably they are a mated pair.

More information

Waite, D. R. K. Food caching and recovery by farmland corvids. Bird Study 32, 45–49 (1985)

Källander, H., 2007. Food hoarding and use of stored food by rooks Corvus frugilegus. Bird Study, 54(2), pp.192-198.

Siskins Galore

 

There is something about birdwatching that I find so rewarding: learning a simple thing, like a species contact call, opens a new world. Although they are regular wintering birds, I don't think Siskins are becoming more common around Hull. It is just that once I learned the beautiful soft, sad 'pew! call, then I am seeing them everywhere, and this year I have really enjoyed watching Siskins. 

Siskin feeding on Italian Alder this afternoon.

In the depths of the winter, when days are gloomy and cold, Siskin flocks rove around the city looking for Alders. They feed on both Common and Italian Alders, clinging from the cones sometimes upside down, deftly extracting seeds with their pointy bills. In quiet areas they might come down and feed on seeds on the ground.

In the last few weeks, the chattering singing chorus of Siskins have alerted me to flocks feeding in Lombardy Poplars in three different locations around the city, possibly as the seeds in Alders are becoming depleted. I was intrigued as I thought these catkins were pollen catkins. Lombardy Poplars are male clones, which produce red pollen catkins. Being wind pollinated I didn't think they had nectar (which would be odd for a finch to eat anyway), but I've never heard of a bird feeding on pollen. What are they feeding on then? Insects, possibly aphids, is a possibility, but it appears unlikely so early in the year.

Male Siskin feeding on Lombardy poplar catkins.

So, a bit like the Goldfinches feeding on lichen covered branches, I don't have an answer to what Siskins are feeding on, but Lombardy Poplars are plentiful around the city parks and playing fields, where they are planted as wind breakers, so hopefully they will stay around a little longer.

Please do let me know in the comments if you know the answer to the mystery!

Waxwing gift passing display

 After a long hiatus, I came across some Waxwings today. Six individuals were perched high up on a Lime tree, taking the sun in. They were quite active, changing branches, pecking the shiny, red tree buds. Two in particular called my attention, as they approached each other touching bills, then coming apart. I took plenty of photos, some unfocused by branches getting in the way, but, looking at them in more detail back at home, I noticed that the two individuals 'billing' were doing more than that, they were exchanging an object, probably one of the tree buds, in a ritual display called 'gift passing' (top shot). The behaviour is seen both in the Bohemian Waxwing, which we get in irruption years in the UK, and in the American Cedar Waxwing. 

The behaviour consist on passing an object, then the individual with the object jumps away, then joins its mate, which 'receives' the object, then the behaviour is repeated and the object passed backwards and forwards repeatedly.

The individual on the left has the gift now.

The individual on the right has it now. Note the raised crests.

Here a Waxwing shows interest in the bright red, shiny buds of the lime tree.

And here, another individual holds some buds in its bill.

I found a description of the behaviour, based on captive individuals and illustrated with photos, which shows that the display is also accompanied from fluffed rump and belly feathers, raised crest and lowered tail, the latest something not very obvious in my photos. The male appears to initiate the behaviour, obtaining the object, and sidling to the female, presenting it. If successful she will accept the object and reciprocate, after jumping away, then close. It is difficult to sex Waxwings, males apparently have longer crests and a more clearly delimited black chin patch.

This is a clip of the behaviour in the Cedar Waxwing, there seems to be a lack of recordings for the Bohemian Waxwing, although the description and my observations fits both species sharing this wonderful display.

More Information

Meaden, F. M. & Harrison, C. J. O. Courtship display in the Waxwing. British Birds 58, 206–208 (1965)