Nectar feeding Blackcap

Yesterday I heard a male Blackcap singing on my way to work. Although it was high on a tree, luckily, I had a small pair of binoculars with me and I found him on a Sycamore in bloom. While I watched it, the Blackcap alternated singing and clearly drinking from the Sycamore flowers, in one occasion clinging upside down from a branch like a tit to reach them. It is well documented that several European birds, especially warblers, regularly drink nectar (I have posted on Blue Tits feeding on Mahonia nectar before in this blog). I could only take some distant shots of this behaviour, and when I got back, I did some research on the nectar feeding habits of the Blackcap.
 The Blackcap is actually one of the most nectarivorous European warblers. Nectar feeding in warblers is most common during spring migration, and has been documented in many stopover sites. Blackcaps often have stained faces due to their flower feeding habits (you can see some examples here and here. This can result on the formation of a 'pollen horn' a matted mass of nectar, pollen and feathers around their bills. Given that their long, thin bill leaves flowers intact after feeding, that they visit many flowers and the presence of pollen on their faces indicating regular contact with the flower's anthers, it is not surprising that Blackcaps can also act as pollinators.
 Experiments on birds trapped during migration indicates that migrating warblers seem to prefer nectar to mealworms when both are offered simultaneously. Nectar feeding is not a last food resort for emaciated birds, but a valuable source of easily digested carbohydrates when birds have reduced digestive systems and high energy demands.
 Blackcaps feed on nectar from a large diversity of flowers, both native and introduced. From the references below, I have compiled the following list of visited plants, which also includes some Mediterranean plants that they encounter during migration, and the Sycamore too. I note the native status in the UK.

1. Goat Willow, Salix capraea. Native.
2. Sycamore, Acer pseudoplatanus. Native.
3. Oregon Grape. Mahonia sp. Ornamental.
4. Citrus trees, Citrus. Mediterranean.
5. Hawthorn. Native
6. Damsons. Here. Native.
7. Almond blossom. here. Mediterranean.
8. Scrophularia. Here. Four large flowered species. Mediterranean, Canaries.
9. Aloe arborescens This female has so much orange pollen on its chest that almost looks like a robin. South African plant widely introduced in the Mediterranean.
10. Anagyris foetida. The only documented native European plant that is exclusively pollinated by birds. Mediterranean.
11. Giant fennel Ferula communis. Mediterranean.
12. Brassica oleracea-group.

More information

Ortega-Olivencia, A., Rodríguez-Riaño, T., Valtueña, F., López, J., & Devesa, J. (2005). First confirmation of a native bird-pollinated plant in Europe Oikos, 110 (3), 578-590 DOI: 10.1111/j.0030-1299.2005.13877.x

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

Schwilch, R., Mantovani, R., Spina, F., & Jenni, L. (2001). Nectar consumption of warblers after long-distance flights during spring migration Ibis, 143 (1), 24-32 DOI: 10.1111/j.1474-919X.2001.tb04166.x

Jacopo G.Cecere, Costanza Matricardi, Beatrice Frank, Simona Imperio, Fernando Spina, Gabriel Gargallo, Christos Barboutis & Luigi Boitani. (2010). Nectar exploitation by songbirds at Mediterranean stopover sites. Ardeola, 57(1), 143-157.

Ortega-Olivencia, A., Rodriguez-Riano, T., Perez-Bote, J., Lopez, J., Mayo, C., Valtuena, F., & Navarro-Perez, M. (2011). Insects, birds and lizards as pollinators of the largest-flowered Scrophularia of Europe and Macaronesia Annals of Botany, 109 (1), 153-167 DOI: 10.1093/aob/mcr255

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