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Tetrapod Zoology

Tetrapod Zoology

Amphibians, reptiles, birds and mammals - living and extinct

Blue tits: passerines seen from the peripheries (part II)

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Preening Eurasian blue tit doing weird stuff with its wing: a bird that I photographed in April 2014. Photo by Darren Naish.

Today I want to talk more about passerines, and I know that this will make you happy. In particular: TITS!! Tits of several species are ubiquitous here in Europe. The two that are most frequently encountered here in southern England are the Great tit Parus major and Eurasian blue tit Cynanistes caeruleus. This article was originally about both species but it became over-long so I’ve ended up splitting it in two.

Oh yeah: again, the ‘from the peripheries’ idea alluded to in the title relates to the fact that western Europe has to be considered a far-flung outpost of the Passerine Empire (see the previous article for clarification). Read on for more about that.

As (just about) every bird-fan knows, all tits excepting the Yellow-browed tit Sylviparus modestus and Sultan tit Melanochlora sultanea were – until recently – grouped together in a large genus termed Parus, conventionally divided into the ten ‘subgenera’ Poecile, Periparus, Pardaliparus, Lophophanes, Melaniparus, Parus, Machlolophus, Cyanistes, Sittiparus and Baeolophus.

The best place to go when wanting to find out about the tits of the world.

But, as more data has come in, people have become increasingly unhappy with the idea that the species concerned should really be lumped into the one mega-genus, and the idea that those 'subgenera' should be stand-alone ‘genera’ has become popular (Gill et al. 2005, Gosler & Clement 2007, Johansson et al. 2013)... albeit not universally accepted among specialists (Päckert & Martens 2008). Decisions like this are always subjective, to a degree. However, in this particular case justification for the idea comes from the fact that morphologically aberrant tits that – in traditional taxonomy – would definitely warrant their own ‘genera’ are known to be deeply nested within ‘Parus’ of tradition. I’m referring to Pseudopodoces humilis, the Tibetan groundpecker: a tit so weird that it was long misclassified as a small ground-jay (and known as the Tibetan ground-jay). Not only is it a member of Paridae, it’s especially close to the Great tit and its relatives, the definitive Parus tits (James et al. 2003) (this has been covered briefly on Tet Zoo before: see links below).

Eurasian blue tit in typical foraging pose. Photo by Darren Naish.

The way the tit family is distributed indicates that eastern and tropical Asia was the main centre of its diversification, with molecular clock data suggesting that most divergences within Paridae happened in Asia during the Middle Miocene (Päckert et al. 2007, see also Johansson et al. 2013). At least two crossings into North America occurred during the Pliocene or Late Miocene; movements west into Europe and Africa happened at about the same time (Gill et al. 2005, Päckert et al. 2007). The taxa that belong to the blue tit complex (see below) diversified during the Pliocene, with the Mediterranean region being the apparent ‘centre’ of their evolution (Päckert et al. 2007). Again, western Europe is a ‘fringe’ region in biogeographical terms – but an important one for migrants that breed further south or east given the ridiculous amount of daylight it receives in summer.

Anyway, we’re here to talk specifically about the Eurasian blue tit. This is a small, garden-frequenting, woodland-dwelling tit, typically about 12 cm long and 11 g, and generally short-tailed and with a unique combination of black horizontal eyestripe, white cheek patches, blue crown and yellow breast. The sexes look similar but with practise you can distinguish the duller-blue females from the brighter males. It can occur at very high densities when conditions are right (as in, two pairs per hectare) and produces one of the largest clutches of any passerine: 7-12 eggs per clutch are about average, and 15 or 16 eggs are not uncommon. The record number is 22.

Diagrams (traced from photos) showing pollinating behaviour in Eurasian blue tits: image from Burquez (1989).

Blue tits of all sorts are typically insectivorous predators that eat huge numbers of caterpillars, aphids, micromoths and other small insects. They also eat seeds and buds, but I’m especially interested in the fact that they also seemingly serve an important role as pollinators. If you watch them often enough, you’ll see them reaching into flowers and emerging with pollen stuck to their faces. However, visiting flowers (and foraging from, or within, them) isn’t the same thing as pollinating them, and the apparent role of Eurasian blue tits as pollinators (especifically of introduced Fritillaria imperialis lilies planted in England) wasn’t brought to attention until 1985 (Ford 1985).

Blue tits are probably only part of a suite of Old World passerines that visit flowers to rob nectar: leaf warblers (discussed in the previous Tet Zoo passerine article) are among the others. What’s fascinating from a historical, evolutionary perspective is the suggestion that some of these birds might originally have been ‘flower-birds’ that formerly took advantage of specialised European plants that became extinct following the Pleistocene glaciations (Búrquez 1989). In the European region, such so-called ornithophilous plants are only present today on the Canary Islands. This puts a new spin on the idea – previously discussed in my article about the 'ghosts' of extinct birds – that ornithophilous plants present across Eurasia might indicate co-evolution with extinct hummingbirds, since it could mean that ornithophilous flowers co-evolved with known, extant Eurasian taxa like leaf warblers, not with hypothesised extinct hummingbirds.

Blue tit visiting flower blossum, presumably for nectar. Note the pollen stuck to the feathering close to the base of its bill. Photo by Darren Naish.

As is so often the case with widespread passerines, the Eurasian blue tit is polytypic – that is, there are several different forms, traditionally regarded as ‘subspecies’. A set of taxa that occur across northern Africa and on the different Canary Islands have conventionally been regarded as C. caeruleus 'subspecies' but they're increasingly regarded as belonging to a distinct species: the African blue tit C. teneriffae. Furthermore, there are suggestions that C. teneriffae is a species complex and that further splitting is needed. Much debate has ensued (e.g., Kvist 2006, Sangster 2005, Kvist et al. 2005). I'm lucky enough to have seen African blue tits on several occasions - much as I'd like to talk about them right now, it'll have to wait to another time. I never planned to write this much about blue tits in the first place anyway, gah! Until next time...

More passerines soon. For previous Tet Zoo articles on passerines, see...

Refs - -

Búrquez, A. 1989. Blue tits, Parus caeruleus, as pollinators of the crown imperial, Fritillaria imperialis, in Britain. Oikos 55, 335-340.

Ford, H. A. 1985. Nectarivory and pollination by birds in southern Australia and Europe. Oikos 44, 127-131.

Gill, F. B., Slikas, B. & Sheldon, F. H. 2005. Phylogeny of Titmice (Paridae): II. Species relationships based on sequences of the mitochondrial cytochrome-b gene. Auk 122, 121-143.

Gosler, A. G. & Clement, P. 2007. Family Paridae (Tits and Chickadees). In Del Hoyo, J., Elliott, A. & Christie, D. A. (eds) Handbook of the Birds of the World. Lynx Edicions, Barcelona, pp. 662-744.

James, H. F., Ericson, P. G. P., Slikas, B., Lei, F.-M., Gill, F. B. & Olson, S. L. 2003. Pseudopodoces humilis, a misclassified terrestrial tit (Paridae) of the Tibetan Plateau: evolutionary consequences of shifting adaptive zones. Ibis 145, 185-202.

Johansson, U. S., Ekman, J., Bowie, R. C. K., Halvarsson, P., Ohlson, J. I., Price, T. D. & Ericson, P. G. P. 2013. A complete multilocus species phylogeny of the tits and chickadees (Aves: Paridae), Molecular Phylogenetics and Evolution 69, 852-860.

Kvist, L. 2006. Response to “Taxonomic status of ‘phylogroups’ in the Parus teneriffae complex (Aves)” by George Sangster. Molecular Phylogenetics and Evolution 38, 290.

- ., Broggi, J., Illera, J. C. & Koivula, K. 2005. Colonisation and diversificiation of the blue tits (Parus caeruleus teneriffae-group) in the Canary Islands. Molecular Phylogenetics and Evolution 34, 501-511.

Päckert, M. & Martens, J. 2008. Taxonomic pitfalls in tits - comments on the Paridae chapter of the Handbook of the Birds of the World. Ibis 150, 829-831.

- ., Martens, J., Tietze, D. T., Dietzen, C., Wink, M. & Kvist, L. 2007. Calibration of a molecular clock in tits (Paridae)—Do nucleotide substitution rates of mitochondrial genes deviate from the 2% rule? Molecular Phylogenetics and Evolution 44, 1-14.

Sangster, G. 2005. The taxonomic status of ‘phylogroups’ in the Parus teneriffae complex (Aves): Comments on the paper by Kvist et al. (2005). Molecular Phylogenetics and Evolution 38, 288-289.

The views expressed are those of the author and are not necessarily those of Scientific American.

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