At the end of April, the arrival of migrant Blackcaps is marked by their beautiful fluty song. Males arrive a few days earlier than females and settle in their breeding territories. I heard the first one in the park on the 19th of April. Blackcaps usually sing from cover in trees and bushes, and the rapidly sprouting leaves will make it more difficult to spot them singing as the spring avances. Today I found a female in the territory where the male had been singing. She was very busy in a tall Sycamore tree, Acer pseudoplatanus, picking aphids from under the leaves, stretching and balancing on the fine branches. The male wasn't far, singing and feeding on aphids like her.
The female feeding.
Note the two aphids on the main veins of the leaf near the male's bill and...
Some birds make nests from scratch, building them from twigs, branches, spider's webs, lichens or mud. Others need a hole to nest on, and they will use natural holes or those drilled by other birds. This post is about two such 'nest snatchers' I've watched recently. In the last few days, I've noticed starlings moving a lot of back and forth between an Ash and the grass lawns in my local park. Yesterday, they were actually using last year's Great Spotted Woodpecker's nest. Woodpeckers have a reputation for feeding on the chicks of hole nesting birds, but they also might be providing them with the nest hole in the first place.
A photo from last year (24th June), with a chick almost ready to fledge calling to its parent (on the right branch)
Yesterday, a Starling getting in the hole
The other nest snatching event happened just in front of my house. There's been an owl box in the Lime tree in front of the house for over 15 years. It was well used, the hooting and gurgling noises of the Tawny Owls from the nest very obvious in the night. A few years ago the bottom of the nest fell off, and the sky was visible from the ground. On Valentine's day the next year the owls called from the nest, probably inspecting it, but it was deemed useless and we stayed owl-less for a few years. This year, Stock Doves showed a lot of interest in the owl house (top shot taken 9th April). They stuffed the box with branches, and miraculously, the branches stayed, the box had been repaired!
The repaired nest, branches sticking out at the bottom.
The booming call of the Stock Doves greeted me in the mornings as I left for work. Until one night we heard a Tawny Own hooting. The owl was actually sitting atop the nest, calling, then flew off low over the roofs. The owls have been calling regularly since, and I guess they have taken possession of the owl box and evicted the Stock Doves.
Tawny Owl watching us from the nest box (20th April).
The finished Carrion Crows nests are very obvious atop the still bare trees. There are several breeding territories I cross on my way to work. Some of these seem to have used the same nest they built last year, others have built another one nearby, the older one still standing strong. If you are lucky you can get a glimpse of the incubating female's head or tail sticking out of the nest. The top shot, I took earlier today, shows that one of the campus pair have decorated their nest with white packaging material. Their nest, on a not very tall alder, is very visible. Only female crows get brood patches during the nesting season: two bare and highly vascularised areas on the chest, which are in direct contact with the eggs and make incubation more efficient. These patches are covered with the feathers surrounding them, which the female fluffs open before sitting on the eggs. The male doesn't get brood patches, and doesn't incubate. During this time, the male feeds the female, and sometimes stands guard near the nest, as this poor photo shows. The female's tail sticking out of the nest on the left and the male sitting on the right. During the breeding period, the male is very protective of the nest area, and these days I see them mobbing Herring Gulls and Sparrowhawks that come near the nest.
There are two territory holding male Goldcrests in my local park. Each appears centred on a large cypress. This morning, over the traffic noise, I head their incredibly high pitched, not very loud song, which appears to come from a tiny violin.
I searched for it a bit halfheartedly, as this cypress is massive, but the Goldcrest just moved onto a smaller one. It fed, as Goldcrest do, in a rush, never stopping, but it did stop for a moment to utter his song and I managed to capture it.
This is a sonogram from the wonderful website Xenocanto of a Goldcrest song:
The pair of Magpies must be around the egg laying stage. Only the female Magpie incubates, while her partner must feed her during this time. Females start begging for food to her partner around the time that they lay their first egg, noisily, wings flapping and uttering what has been described as the 'clear call'. The success of a pair of Magpies depends on how good the male is at keeping his mate well fed. A hungry female is more likely to take breaks from incubation, leaving the eggs exposed to predators (most likely Carrion Crows, according to T.R. Birkhead, the archenemy of Magpies).
Yesterday afternoon, I heard this peculiar Magpie call repeatedly from the garden. The pair of Magpies were at a birch tree and one of them (the one on the top, likely the female), flapped her opened wings, chasing and begging to the other, quite indifferent, individual, likely to be the male. I took a video of this behaviour you can watch below (you might need to turn the volume up to hear the call).
The other day I watched a Collared Dove attacking a Woodpigeon. I was a bit puzzled by this bit of seemingly random aggression, as the Woodpigeon was on its way to drink.
The following day in the same spot, a Collared Dove sat on a branch, quite low and I thought that the Collared Dove's puzzling behaviour might have to do with it's nest being nearby.
This morning I thought that the Collared Dove was sitting in the same spot, but when I approached I noticed the fuzzy fluff and less pink plumage of a fledgling. Completely unafraid of me, it looked curious as I took its portrait.
This is the 3rd pigeon species that I have seen fledglings this year, the first one was a Feral Pigeon, then a Woodpigeon last week. Not wasting any time!
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.
Toshitaka, S. N., Wheatcroft, D. & Griesser, M. Experimental evidence for compositional syntax in bird calls. Nature Communications (2016). doi:10.1038/ncomms10986