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

Goldfinches and dandelions

You don't need to get out much to enjoy wildlife. Literally, sometimes surprising things happen right at your doorstep. This morning I had to stop short of opening my front door as I realised a pair of goldfinches were standing next to it. One of them was grabbing a couple of dandelion heads - that had probably tumbled over with its weight - and feeding on the unripe seeds. This went on for quite a while. The photographs were taken through glass.

Goldfinches are specialist on small seeds, they benefit greatly from flocking when foraging as they need a lot of effort to obtain enough biomass from tiny seeds that have to be prepared and swallowed one by one and they can devote less time to scanning for predators when they are in a flock.

Gluck investigated these effects on Goldfinches feeding in orchards in Germany during the breeding season. He recorded Goldfinches feeding on milky ripe seeds from 20 plant species. Of these, most of his observations were on five species: Dactylis glomerata (Gramineae), Knautia arvensis (Dipsacaeeae), Senecio vulgaris, Taraxacum officinale and Tragopogon

pratensis (Compositae). The following graph illustrates the relationship between the number of dandelion seeds ingested per minute and flock size in Goldfinches, showing that even in small flocks of 5 birds each bird can almost double their seed intake per minute.

I am a big fan of dandelions and today's sighting is going to make me do even less weeding around the garden.

More information

Erich Glück (1986) Flock size and habitat-dependent food and energy intake of foraging Goldfinches. Oecologia, 71:149-155.

Worms, quick, quick!

Blackbird fledglings are out and about. Their urging 'quick, quick' calls to their parent to bring food make them easy to track. If the female is not ready to lay a second clutch, the pair of Blackbirds will divide the care of the brood amongst for up to ten days after the young leave the nest. If the female has already started laying, then the male takes care of the whole brood, running back and fro in search of food for his demanding young. This behaviour is a trade-off: the male taking charge allows shorter intervals between broods - and therefore higher chances that more chicks are produced in a season - but the more young he is feeding, the lower the chances they will all reach independence.
Yesterday, a male sang while it flew toward his charge, like he didn't want to waste a minute - a stressed, multitasking parent. Then, landing nearby, caught a large earthworm and banged it against the ground several times while the fledgling called insistently. The male offered the worm to the young, and he swallowed it voraciously.

Gradually the young will learn to catch prey or find food by themselves, and by 2-3 weeks after leaving the nest they will reach full independence.

More information:
PHILLIP J. EDWARDS (1985) Brood division and transition to independence in Blackbirds Turdus merula. Ibis, 127: 42-59. here.

Nest Calling Woodpigeons

Woodpigeon pairs are already formed and nest building is underway. For quite a while I have become accustomed to an unusual song of the Woodpigeon. It starts like it is going to deliver the usual five-syllable song, but instead it stalls and it only delivers two long notes, 'coo, coooo' with the second note dragging on - it reminds me or a revving motorbike. After a minute or so, the two notes are repeated, and it can go on like that for quite a while. I have heard it mostly when the pigeon is concealed from view (inside a cypress) and in one occasion I saw it delivered by a pigeon sitting on its nest. A pair of Woodpigeons have made a nest on a fork in a large weeping willow and the pigeon in the photo was calling in such a way. This call has been named 'the nest calling' and is uttered by the male showing the female a nesting site. According to Murton and Isaakson:

Nest calling is a submissive display, mainly shown by the male and is used to attract the female to the nest or potential nest site. Caressing can occur at the same time as nest calling or away from the nest, and possibly evolved from the food begging movements of the nestling. It usually precedes courtship feeding. On the physical level the display is used to stimulate ovulation in the female, so that when used for long periods in the absence of courtship feeding it appears as a ritualized display.

And according to Cramp:

From early January, and often soon after the pair is definitely formed, the male begins to mark suitable nest sites by Nest Calling. He crouches on the proposed site (which may be a bare fork or branch, or an old nest) and makes short, sharp, downward pecking motions, 

accompanied by the special nest call—a deep, double note, `coo, coo'.

The male may `nest-call' at several sites, and I imagine that the female normally makes the final choice, for the nest is by no means always built on the site where her mate has `nest-called' most persistently. The first nests are seen normally towards the end of March, and the majority start to sit in April.

More information:
Cramp, S.(1958) 'Territorial and other Behaviour of the Woodpigeon', Bird Study, 5: 55-66.here.
Murton, R.K., A. J. Isaacson (1962) The functional basis of some behaviour in the Woodpigeon Columba palumbus. Ibis: 104: 503-521. here.

Eight things I didn't know about swifts

The first Swifts are back! These extremely aerial birds spend just three months of each year with us, from early May to early August - their breeding season - but their continuous flight and noisy chases makes them obvious and fascinating birds to watch. They eat, sleep and mate and collect their nest materials on the wing. I recently read "Swifts on a Tower" by David Lack. A very informative and entertaining book, it is based on the observations of David and Elizabeth Lack and their students. They observed nesting swifts on modified nesting holes in the tower of the Oxford University Museum of Natural History, a building of fame due to being the place where the famous debate on evolution took place between Samuel Wilferforce and Thomas Henry Huxley seven months after the publication of the Origin of Species.

Museum of Natural History (Oxford) the central tower ventilation shafts (10 on each side) are the entrances to the Swift nests. Photo by Michael Reeve, licensed under Creative Commons, from Wikipedia.

Based on this book and more recent research I have compiled this list of facts that I didn't know about swifts.

1. Their young can survive up to 21 days (!!!) with no food. Their growth patterns match the weather so that they stop growing during cold, wet or windy weather. The length of time they take to leave their nests depends as well on the weather, the earliest leave at 5 weeks, the latest at 8 weeks.
2. Eggs can get cold (i.e. left by the adults without incubation) for at least two days and survive.
3. Swifts - and possibly other bee-eating insects - can distinguish drones from bees and drones are the ones they eat, avoiding getting stung by workers.
4. Swifts fight for their nests cavities by grasping each other's claws. The winner is the individual that can get on his back, so that it can push the other out of the nest.
5. Adult healthy swifts can indeed take off from the ground. It is the recently fledged individuals in not so good condition that can't (they leave the nest early and their wings are not fully grown.
6. Once fledged, young swifts are completely independent and receive no further parental care. They return to their summer grounds to breed when they are 3-4 years of age.
7. The young join non-reproducing birds to sleep on the wing high up on the sky.
8. Swifts are the fastest birds during self-powered flight (the peregrine "free-falls" using gravity to accelerate) reaching over 110 km/h in their 'screaming parties'. More info here.

More information:

For an informative article by the 'guardians of the tower' see here.

Henningsson, Per, Johansson, L. Christoffer, Hedenström, Anders (2010) How swift are swifts Apus apus? Journal of Avian Biology, 41: 94-98. Here.

Check the fantastic photos of swifts on flight by Jean-Francois Cornuet here.