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

Woodpigeons and Holly

 There is a mature holly on a street in my way to work. It's leaves don't have any thorns and it is a very lush female specimen. A few weeks ago it was an impressive sight, laden with bright berries. All through October and November, it has been visited by Woodpigeons, balancing precariously and gorging themselves on the berries.

Planes and goldfinches

This morning coming into work I heard the unmistakable chirps of squabbling goldfinches. There was a large flock feeding on a line of plane trees. While I climbed the stairs I thought delightedly that the window in our lab overlooks the trees, so I could have a level view of the feeding goldfinches. There they were, hanging from the bauble-like seed balls or balancing from the thin stems holding them. London plane trees (Platanus x acerifolia) is an important food resource for goldfinches, as it provides seeds during the autumn months into the winter. The photos didn't come brilliant - I blame the dirty windows - but I think the one on top captures the atmosphere of the feeding flock. I count seven, how many can you see?

More information

Sachslehner, L. M. (1998): The significance of Plane-trees Platanus x hispanica M. as a food resource for Goldfinches Carduelis carduelis L. in Vienna. Egretta 41: 90-101.

Beach Rooks

The last couple of times I've been at Hornsea beach I've been surprised by the gang - sounds more appropriate than the collective names of "building" or "clamor" - of rooks. They feel at ease cruising the beach up or down on the sand, gliding over the waves or over the promenade wall in search of morsels of food. They look like rooks that tried to be a seagull and they quite liked it. I love how incongruous they look with the blue backdrop of the sea, but also how the behaviour of this particular group of individuals illustrate how resourceful corvids are.

Eats shoots and leaves and buds and flowers

A woodpigeon feasting on cherry flowers. I have seen them in the last few weeks eating cotoneaster berries and poplar buds (or catkins, hard to say). Come May, they will take advantage of Horse Chestnut flowers too. The one below has stretched all she could to strip bare two inflorescences, they are quite tricky to reach, but woodpigeons are not scared to stretch their necks and almost hanging upside down to reach the best bits!

The bumblebee tit

Today I watched a pair of Blue Tits paying a lot of attention to the inflorescences of Mahonia in the local park, coming back to them again and again. What were they doing? If you hear nectar feeding in birds you would most likely think on hummingbirds and the tropics. However, several bird groups feed regularly on nectar in addition to hummingbirds, honeyeaters and sunbirds. In Australia, birds are actually the main flower pollinators. Although nectar feeding behaviour in Europe is far less widespread, it does happen. In 1985, Hugh Ford reviewed the handful of studies suggesting or indicating nectarivory in European birds (see table below).

 Most of the species were warblers, with the Chiffchaff and the Black-cap the most cited ones. Warblers winter in southern Europe or Africa, where there is a larger proportion of bird-pollinated flowers and where nectar feeding in birds, is more widespread. They are also known to exploit nectar while migrating, as a quick way to gain energy. The bird species that most commonly feeds on nectar in northern Europe, however, is - you guessed it - the versatile Blue Tit. Blue Tits seen on flowers are often thought to be foraging for insects, or feeding on parts of the plant, such as petals. However, Blue tits have been recorded feeding on a range of flowers, both introduced garden varieties and native ones: Gooseberries, Flowering currants, and the Fritillary Imperial Crown. What is more, Fitzpatrick, studying suburban blue tits, found that nectar can make a substantial part of Blue tit diet in early spring. Feeding on flowering currant inflorescences, Blue tits chose the most productive flowers, those with a darker pink rim. They used two strategies to get at the nectar: pecking the corolla out to reach the nectaries, or perforating a hole on the side of the flower - bumblebee style - to reach the nectar directly, as the flowers are too narrow for them to insert their beaks, and therefore cause quite a deal of flower destruction. Coal Tits were also observed feeding on the Flowering Currants, but they inserted their more slender beak into the flower and thus did not destroy the flower in the process of feeding.
   The Fritillary imperial crown is an impressive red or yellow flowered bulb in which a whorl of wide, flowers hang from a stout bare stem. It originates from Asia but is widely planted in the UK. Búrquez, showed that Blue tits not only collect nectar from these flowers, but they also act as are efficient pollinators of the plant.

  Blue tits in native habitats are often seen feeding on willow blossom, so nectar feeding seems to be another of the wide variety of opportunistic behaviours used by this tit to use resources.

More information
Ford, H. (1985). Nectarivory and Pollination by Birds in Southern Australia and Europe Oikos, 44 (1) DOI: 10.2307/3544053

Búrquez, A. (1989). Blue Tits, Parus caeruleus, as Pollinators of the Crown Imperial, Fritillaria imperialis, in Britain Oikos, 55 (3) DOI: 10.2307/3565592

Fitzpatrick, S. (1994). Nectar-feeding by suburban Blue Tits: contribution to the diet in spring Bird Study, 41 (2), 136-145 DOI: 10.1080/00063659409477210

One, two, three...ten long-tailed tits

This time of year, the shrill 'see,see,see' contact calls of Long-tailed tit flocks, coming from all directions from the tree canopy. These fluffy, tiny birds have a fascinating breeding system - facultative co-operative breeding - by which individuals may help rear up offspring of others depending of the circumstances. Their breeding season is rather short, and they are only able to rear a single brood per season. In the spring, all individuals pair up and attempt breeding, if breeding fails early enough - mostly due to predation - , they attempt nesting again.

A predated nest of long-tailed tit on the 25th of April this year, the intact nest is a ball with the outside made of a delicately shell of pieces of lichen attached with spider webs, the inside is a down and feather filling. It can take the pair up to three weeks to put together.

In contrast, if a brood is lost late in the season, individuals may turn to help other nest owners raise their brood, bringing food for their offspring, and actually increasing the fledging rate. Who do long-tailed tits help? The theory of kin-selection predicts that individuals should help their relatives for cooperative breeding to persist. Do long-tailed tits do this? How good are they discriminating their kin? Is the amount of help correlated with the degree of kinship? Prof. Ben Hatchwell, from the University of Sheffield, has been studying a population of long-tailed tits for over 14 years, and his research has provided wonderfully detailed insights on the reproductive behaviour of the long-tailed tit. Apparently long-tailed tits are able to recognize their kin through their contact calls. In a new study by Prof. Hatchwell's group, kin relationships between most individuals in a valley near Sheffield (U.K.) were assessed using pedigrees and genetic markers. Then they followed the nesting attempts - on real, amazingly cryptic nests, not in nest boxes! - and estimated provisioning rates by the different carers. This way they were able to document the relationships between helpers and the individuals they helped.

The first interesting result, is that social ties are very good predictors of paternity in this species, there were no instances of cukoldry. Pairs were monogamous for each breeding season. This meant that pedrigree data was a very good predictor of genetic relationships.
  In many other cooperative breeders helpers often provision their siblings - that is, they are previous years offspring that delay they reproduction to help their parents raise another brood. In the case of the long-tailed tit, helping another nest is dependent on an own nesting failure, and there is a lot of diversity. Individuals can help their offspring, one or both parents, aunts and even a case of an individual helping a grandparent!. Most of the cases, however, involved individuals helping their siblings rear their nieces and nephews. This is possibly related to the high 'divorce' rates in long-tailed tits. Pairs are monogamous during a particular breeding season, but mortality is high (50% from one season to the next) and individuals often switch partners, therefore, the chances of a individual helping their parents is reduced. Also, siblings often disperse together to new territories so there is more opportunities to help a sibling than any other relative. In conclusion, most cases of help were to relatives, supporting kin-selection theory. However, things are often more complex than that: 23% of the helpers actually helped unrelated individuals. When the researchers looked at this in detail they saw that they were unrelated, but not unknown. Individuals helped other individuals with which they had social ties: previous year's partners - no hard feelings! or they helped in nests where another 'ex' was also helping. Maybe there is an element of reciprocity there. These results could make you think that long-tailed tits help guys they know, and the fact that they often help kin is just but the consequence that they tend to know their siblings socially, but it is more interesting than that.
Another, key prediction of kin selection theory: helpers should invest more the more related they are to the individuals they help (that is, helping is a cost and they should adjust the costs to the benefits). With their data of provisioning rates, they could indeed confirm that this is true: helpers provisioning rates increased with the relationship to the nestlings they fed.
Therefore long-tailed tits do recognise kin and preferentially assist them, providing support for the role of kin selection in the evolution of their breeding behaviour.
At the end of the breeding season, family groups come together in flocks, that will joining other tits and small birds and wander around the canopies throughout the winter.


More information
Nam, K., Simeoni, M., Sharp, S., & Hatchwell, B. (2010). Kinship affects investment by helpers in a cooperatively breeding bird Proceedings of the Royal Society B: Biological Sciences, 277 (1698), 3299-3306 DOI: 10.1098/rspb.2010.0737