Great tits feeding on horse-chestnut leaf miner

In a walk around the local park, a pair of Great Tits called my attention. They were calling and foraging in a horse chestnut. I watched how dexterously they grabbed the large leaves with their bills, pulled them towards them, and held them with one foot while feeding (top shot). They were looking for larvae or pupae of the horse chestnut leaf miner, Cameraria ohridella, a micromoth that has expanded its range throughout Europe from its native Balkans. The moth's larvae feed inside the leaves of the horse chestnut, leaving them speckled. Blue tits also feed on this leaf-miner (as do Marsh Tits), and I've seen them feeding on them before, but as they are lighter than Great Tits, they are able to just hang from the leaves themselves.

A short clip demonstrating this behaviour.

More information
Grabenweger, G., Kehrli, P., Schlick‐Steiner, B., Steiner, F., Stolz, M., & Bacher, S. (2005). Predator complex of the horse chestnut leafminer Cameraria ohridella: identification and impact assessment. Journal of Applied Entomology, 129(7), 353-362.

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

Great tit holding seed

A Great tit holds a seed that just fetched from a bird table. Tits in general are dextrous birds, and often manipulate seeds or fruits before consumption. There are many passerine birds that hold food with their feet, from a total of 20 families in a revision on the topic by George Clark. Other examples include Carrion Crow, Rook, Siskin, Goldfinch and Crossbill.

More information

Clark, G. A. (1973). Holding food with the feet in passerines. Bird-Banding, 91-99. here.

Singing Great Tit

This Great Tit was singing enthusiastically from a tree today. I whistled its 'tea-cher' song and, curious, it came out more in the open, showing its black chest band, head high.

Birds and sycamore aphids

Sycamore aphids, Drepanosiphum platanoidis, are Sycamore specialists - and cover your car with honeydew if you happen to park underneath. All adults are winged and sit evenly spaced under leaves. In the spring, sycamores come alive with the calls of hungry Blue Tit fledglings demanding food. It is an easy job for the adults to pick the aphids from under the leaves to feed the chicks (above). Although many leaves have fallen now, there are still some in the sycamores, peppered with the black spots of, Rhytisma acerinum, the tar spot fungus, and some aphids are still in them. In the last few weeks I have seen Great Tits and Chaffinches feeding on them. Today, I watched a chaffinch hovering under the leaves picking the aphids, a most beautiful sight, which unfortunately couldn't catch on my camera.

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