Herring Gull pair long call duetting

You have probably seen Gibbon pairs duetting in nature documentaries or videos. It is a territory display that shows how the pair is well bonded, and the turn-taking of the duetting is amazingly precise, the pair alternating calls to produce a single 'song' that advertises their presence and ownership of a territory. But you don't need to travel to distant tropical jungles to witness pairs duetting animals. Herring Gulls do it all the time. Because their long call is so familiar we tend not to pay much attention to it, but I was made to stop a couple of days ago when a pair landed on a chimney stack opposite my house (above). One of the pair seemed intent on long calling, and started to call, followed each time by its partner. Long calls become commonplace during the breeding season, when pairs defend territories or food, as it appears to have an aggressive function. Here is a sonogram of it. The gull starts calling with the neck pointing down, the calls well spaced, then the calling becomes faster in a staccato and the gull stretches its neck and points up and then the call dies in intensity. In 'The Herring Gull world, Tinbergen describes the call, saying that 'The voice of the herring gull is wonderfully melodious’‘There are few sounds as evocative, as stirring as the profound, plaintive beauty of their calls.' However, he missed the fact that it often occurs in pairs, there the pair message is not to each other, but to other gulls. The duetting has also been described in other gulls, like in the Western Gull.

A pair of Herring Gulls with their two young duet on a roof in Filey.

Often, one of the pair starts the call, and the other joins in and they end the long call together, necks stretched, bills pointing up.
Why do gulls long call? They seem to do it when they have asserted their ownership of something (food, for example) or finish a squabble, or sometimes the whole Herring Gull colony calls and pairs joins together. I'm surprised I've found so little about this amazing behaviour other than anecdotal references to it, but this is a wonderful photo of a pair duetting.

More information

An article on long calls in various gull species. Earbirding.

Mute Swan acoustic communication

I've said it before, Mute Swans are not really mute, they have a repertoire of calls and sounds. They also use movements of their head and neck to communicate. There is a quick head bowing movement, and a courting movement in which the feathers at the top half of the neck are ruffled, while those at the bottom are not, while the swan bows his head alternatively to left and right; and the aggressive 'busking stance' of the territorial male. In this post I focus on sound communication. I have trawled through Xenocanto, an encyclopaedic website with thousands of bird calls, to compile the following selection of Mute Swan sounds. I was prompted to write the post after listening to an odd distant call, which I didn't recognise to start with, and I was surprised to find out that it was a mute swan's. I heard the call again today, young swans calling to a swan flying overhead. It is not straightforward to distill the 'meaning' of a call, but the context can helps.

1. Snort

A short grunt or snort, often uttered when the swans are relaxed, and appears as a contact call while feeding, between members of a family, but also a greeting call. A lone young swan snorted when I walked by a lake near him.

2. Begging call

A soft repeated whistle typical call of young. Mute Swans don't 'feed' their young by putting food in their bills, but they help the young to obtain their food by paddling with their feet to  disturb the sediments or by pulling underwater plants. Even fully grown immature swans carry on whistling.

  3. Wing-beat Sound

This loud sound produced by the mute swan's wing-beats is really eery, especially when it takes you unawares until you realise that is coming from a swan. It carries very well and appears to replace the trumpeting contact calls of other swans.

4. Hissing

An aggressive sound, usually uttered by the female she has small young and a danger (human, dog) approaches. The bill is open and the swan adopts an upright stance towards the danger source.

5. Contact all

A two-note contact call reminiscent of other swan's flight call. I heard this call when a pair was separated, maybe during landing (one ended up in the river, the other one in a lake). Also when a Mute Swan flew over a family, the juveniles used this distance call.

6. Courtship calls

A range of snorts and grunts during courtship.

 Have I missed any? Let me know in the comments.

The bristle head crows

Carrion Crows have a complex social structure. Territory-owning Carrion Crows remain paired year round, often flying and feeding together or not far from one another. They remain near their nest during the breeding season, although they may range wider outside this period. Birds that don't hold a territory form part of a loose flock that roosts communally, usually in large trees. Both male and female of a pair participate in territory defence, keeping other crows (or potential predators) away from the nest. Males have a more prominent role: if a male loses his mate he is able to defend the territory until he remates, but a female losing his mate will also lose her territory, as she would rapidly be evicted by other pair.
In one of my local parks there is a very high density of Crows. There are several territories, but the park is also the main ranging area of the non-breeding flock (where there is also a winter roost). There are a lot of interactions going on, but without ringed birds, it is hard to make sense of what is actually happening. Yesterday, I observed several interesting interactions. First, a Black-headed gull appeared most annoyed with a Carrion Crow and mobbed it repeatedly, dive-bombing on it when the crow tried to stop on an aerial. The crow did not vocalise and deftly avoided the gull attacks. Later, I heard the rattling call of a crow and watched a chase between two crows, one of them calling with the call I usually associate to mobbing a raptor. Crows, it appears, can use this vocalisation to fend off conspecifics.
 Finally, I watched a Crow it an amazing display: its head feathers raised, bill pointing down, looking really at its best. After taking a few photos, I realised it's partner was walking nearby using the same posture. Today I learned about this display in 'The Crows' by Franklin Coombs. It is called the 'Bristle head' display. It is a territory-owner display, used in territory boundaries to signal their occupancy, and also aimed at intruders within the territory. Both members of the pair display while they walk about. There is no vocalisation. Territory intrusions mostly occur during the spring, but there is also a peak in October-November.
 I can only presume that this pair of crows are a pair ot territory owning breeders. They do look in great shape!

This is a still from a video, which shows both members of the pair with their 'bristle heads'.

A side view of the displaying crow. 

This photo is a bit overexposed, but it shows the details and metallic iridescence of the crow really well.

Great Tit grammar

Winter is tough for small birds. The bare trees and the need to spend more time finding food to compensate for higher energy demands in cold weather means that they might be more exposed to a range of predators. They often join other birds in mixed flocks which might afford them more protection, as more eyes keep an eye for Sparrowhawks or cats. Birds have another card up their wings: alarm calls. Alarm calls can be very diverse and research has shown that they can be specific to each predator: responding appropriately is crucial, therefore alarm calls have meaning: flying away might be good if a cat is about, but staying still or hiding in a bush might be a better response to an aerial predator. Tits are highly vocal and have a broad repertoire of calls, which they repeat in different combinations. Some calls are used to beckon other tits when food is found, others to mob predators, yet others as contact calls. They are also very responsive and inquisitive and will approach to you if you imitate them.
 A research team from Japan, Germany and Sweden, led by Toshitaka Suzuki, has been investigating communication in Japanese Great Tits, Parus minor, a close relative of the European species that used to be considered a subspecies (the photo above is of the European Great Tit). Using playback experiments of natural and artificially manipulated calls they show that Great Tits responded very differently to different calls. One call, which they named D call (also called the 'jar' call), is used by birds that are alone, and their partner is more likely to join them after hearing the call, a 'come and join me' call. When researchers played this call on a loudspeaker, great tits approached the loudspeaker. Another call, ABC calls, also called 'chicka calls' are used in an anti-predator context, and playback calls elicit scanning behaviour like the tits are looking for potential danger, 'watch out'. Often tits combine different calls are combined in different sequences, as we combine words in a sentence, for example they add their D call to the ABC call, e.g. ABC-D: upon hearing this, the birds watch left and right as it searching for a predator in their surroundings, but they also approach the loudspeaker, so that both calls combine the separate meanings into a 'sentence', which is used in a mobbing context.
This video shows the sounds separate and in combination, and illustrate how similar the Japanese Great tit calls are to European great tits.
 The researchers wondered if the order of the call matters, that is, there is syntax in the vocalisations. If order is important, then the birds should respond to the ABC-D but not to an artificially generated D-ABC call. They played both calls to 34 wild Japanese Great Tits individually in the winter and counted the number of scans and if the birds approached the loudspeakers. These were their results:

Responses of Japanese great tits to playbacks of ABC–D and D–ABC calls (a) Number of horizontal scans made by tits in 90 s (b) Percentage of trials in which tits approached within 2 m of the loudspeaker. From Suzuki et al 2016. This Creative Commons Attribution 4.0 International License.
The birds scanned and approached the loudspeaker much more when the natural ABC-D call was used, strongly suggesting that the meaning of the vocalisation is lost when the natural order is altered, and that, indeed, birds use grammar. The combination of calls in the context of grammar enriches the possibilities of meaning of a limited number of calls, making bird language much more fascinating and complex that we could have anticipated.

More information
Toshitaka, S. N., Wheatcroft, D. & Griesser, M. Experimental evidence for compositional syntax in bird calls. Nature Communications (2016). doi:10.1038/ncomms10986

Canada geese head tossing

The Canada geese with a broken wing is now in the company of his partner in the park, who didn't leave with the flock in early March to their breeding grounds. He managed to retain two other individuals for a while - maybe offspring from previous years, as Canada Geese have long term family ties - but they ended up leaving. This morning, somebody started feeding the birds on an end of the pond, and I saw the pair of Canada swimming towards the feeding point. Broken Wing was leading his partner. He kept tossing his head every few seconds, and after a few tries I managed to capture the behaviour (above). It felt like a 'hurry up, follow me!' beckoning to female. Indeed, Canada Geese often communicate using head movements. I have covered the pre-flight head tossing, which is accompanied by much calling. When on land, and during the flightless phase of chick rearing during the moulting period, head-tossing by itself indicates readiness to walk or swim and is used especially when they are very motivated to move. Head tossing is very conspicuous due to the white cheek patch, and this is often directed to family members. Individuals head-toss when stationary, appearing to signal to other family members to follow them, including females to young goslings, and the signal is continued during movement. The direction at which the head is tossed is also informative, indicating the direction of movement. Even young goslings - who don't have the white patch - start head tossing in the first day after hatching, signalling their intention to move to other foraging patch. In a situation of threat, e.g. when a predator is located, this visual signalling allows parents to quietly direct their goslings to cover, avoiding attracting unwanted attention by acoustic signals.

More information

Jeffrey M. Black and James H. Barrow, Jr. (1985) Visual signalling in Canada geese for the coordination of family units. Wildfowl, 36, 35-41. Available here.

The scary bright eyes of the Jackdaw

Jackdaws breed in loose colonies, and unusually for corvids, in cavities in trees, cliffs or buildings. There is often very strong competition for nest sites, and the pair will defend their nest fiercely against conspecifics. Jackdaws are also unusual for having very contrasting, almost white irides. In a recent paper, Gabrielle Davidson and her colleagues from Cambridge and Exeter Universities tested the hypothesis that the bright, contrasting eyes of the Jackdaw serve as a strong warning signal when adults are occupying a nest, warning intruders not to come in.
 They set up 80 identical nest boxes in woodland areas in Madingley (Cambridgeshire) during the pre-breeding season (February-April), when Jackdaws prospect potential breeding sites. The nest boxes had two perches, one at the base and the other just by the entrance. They fitted the inside of the entrances of the nest boxes with a circular printout, visible from the outside. Each nest box was randomly assigned one of four types of printout: a dark circle (control) a dark circle with white 'eyes'  of the same dimensions of a Jackdaw (eyes only), a printout of a face-on photo of a Jackdaw with eyes retouched to increase the brightness (bright eyes), and the same printout but with dark eyes (dark eyes). They used remote video cameras to record Jackdaw visits to the nests, and the time they spent sitting on the nest itself and the perches.
 The results were striking. Jackdaws alighted on the nest box significantly less when the bright eye print was in the nest entrance. In addition, they spent very little proportion of their visit time on the perch closest to the entrance both in the eye only and bright eye treatments. The visiting Jackdaws actually entered the nest box in two occasions, one in the control and another one in the dark eye treatment.

This experiment shows that eye colour can be important in communication with conspeficics. The pale eyes are a warning signal to prospecting Jackdaws that a nest is occupied, and they avoid approaching the nest entrance once they are on the nest box. This reaction to an occupied nest reduces intraspecific conflict, as it might save them from a fight and potential injury. Davidson et al speculate that the 'eye fear' response of Jackdaws might be more general, and they might react in the same way to sparrowhawk eyes, for example, as it is known that they are sensitive even to eye gaze in humans - they will delay their approach to food if a human is looking at them.

More information
Davidson GL, Clayton NS, & Thornton A (2014). Salient eyes deter conspecific nest intruders in wild jackdaws (Corvus monedula). Biology letters, 10 (2) PMID: 24501271

Tail flicking Moorhens

The contrasting white feathers at the sides of Moorhen tails are very obvious, especially when they flick their tails up and down, often fanned. As this one run away from me this morning I wondered what is this flicking for? An aggressive signal to other moorhens had been proposed as a hypothesis. However, observations carried out by Fernando Alvarez suggested a more intriguing reason. When a patrolling Marsh Harrier - a common predator - approached a moorhen, the rate of tail flicking increased as the moorhen dashed towards cover. In addition, the more vigilant the bird, or the further away from cover, the higher the tail-flicking rate was. These and other results suggested that tail flicking is not a signal to other moorhens, but a signal of alertness to the potential predator: 'I can see you!' This might deter the predator from chasing that alert individual and try catch a less vigilant one unawares.
 More experiments by Alvarez and colleagues suggested that moorhens in better physical condition showed higher flicking rates when foraging: healthier individuals flick their tails faster, which indicates that the signal is actually telling the predator: 'I can see you and I am fast so you can't catch me!
So both prey and predator would benefit from this honest signal of body conditions and alertness, as a chase, which would be wasteful in energy for the prey and likely to be unsuccessful for the predator, is avoided.

flicking away from me

she is definitely seen me!

she looks quite alert, but maybe then realised I pose no danger

UPDATE 3/10/2013

I took this video today of the tail flicking behaviour in the park moorhens

More information

Fernando Alvarez (1993). Alertness signalling in two rail species Animal Behaviour, 46, 1229-1231 DOI: 10.1006/anbe.1993.1315

Fernando Alvarez, Cristina Sánchez, & Santiago Angulo (2006). Relationships between tail-flicking,morphology, and body condition in Moorhens Journal of Field Ornithology, 77, 1-6 DOI: 10.1111/j.1557-9263.2006.00001.x

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