Today I’d like to focus on passerine birds again, and this time on a group that I don’t think I’ve ever blogged about before: the certhioids. Scrap that. This article ended up being devoted entirely to just one lineage within Certhioidea: the nuthatches, or sittids (properly Sittidae). We start with the image above, taken in an English woodland here in Southampton, showing a Eurasian or Common or Wood nuthatch Sitta europaea. The Eurasian nuthatch is a mid-sized member of the nuthatch family, and by far the most widespread: it occurs from western Europe all the way east to Japan, also inhabiting parts of Morocco, various parts of the Middle East, and then eastern China, North and South Korea, and Taiwan.

As is the norm for birds that have ranges this extensive, a large number of ‘subspecies’ have been named. About 22 are currently recognised, grouped into three 'subspecies groups' (the 'caesia group', 'europaea group' and 'sinensis group'). As is also 'the norm' for polytypic assemblages of this sort, some of those 'subspecies' look (and sound) ‘distinct enough’ to quality as species in their own right, most notably the Siberian nuthatch S. e. arctica/S. arctica. Many European populations - those belonging to the 'caesia group' - have white cheeks and throats but are otherwise buff underneath and reddish around the vent. Meanwhile, races from Scandinavia and many parts of Asia (members of both the 'europaea group' and 'sinensis group') have far more white on their bellies and flanks, while other 'sinensis group' populations are extensively orange-buff ventrally and lack white almost entirely. [Adjacent photo by Pawel Kunźiar/Jojo].

The distribution of the Eurasian nuthatch in the UK is quite interesting in that it’s almost wholly absent from Scotland and is missing completely from Ireland. It has been spreading north over the past several decades, however, and first bred in Scotland in 1989 (Enokksson 1993). It’s thought that this spread is related to its increased use of bird tables. As is obvious given the fact that the bird has failed to even cross the Irish Sea, the Eurasian nuthatch is a very sedentary bird. Individuals move little during their lifetimes, pairs stick to the same territory year-round, and there appears to be no exchange between the birds of Britain and those of continental Europe. The Siberian nuthatch, however, is known to move westwards as far as Finland during severe winters.

S. europaea is one of about 28 Sitta species, the members of which occur across Europe, Asia, northern Africa and North America. Some authors have suggested that Sitta should be split up into four genera (Dickinson 2006). However, the taxa suggested to be deserving of their own genera (oddballs like the Beautiful nuthatch S. formosa and Blue nuthatch S. azurea) are – based on their position within a recent phylogeny (Pasquet et al. 2014) – deeply nested within Sittidae so, if they were given their own genera, a new taxonomy for the entire group would need to be devised. Of course, there are lots of old generic names that would be resurrected if that were to happen: Leptositta Buturlin, 1916 for the White-cheeked nuthatch S. leucopsis, Poecilositta Buturlin, 1916 for the Blue nuthatch, Cyanositta Buturlin, 1916 for the Velvet-fronted nuthatch S. frontalis and kin, Rupisitta Buturlin, 1907 for the rock nuthatches, and so on. [Adjacent photos by Jimfbleak, Snowmanradio and Devonpike.]

In western Europe, S. europaea is a familiar denizen of deciduous and mixed woodland but it’s more strongly associated with coniferous forests in northern Europe and Asia. In fact, many nuthatches are associated with conifers. Several species – the so-called rock nuthatches – frequent environments where large expanses of bare rock are important. Given the fact that rock nuthatches are, again, nested within the nuthatch radiation (Pasquet et al. 2014), it has to be assumed that the lineage concerned made the transition from tree-climbing to rock-climbing at some point in their history. As someone interested in form-function correlation and how claw morphology correlates with lifestyle (or doesn’t) (Birn-Jeffery et al. 2012), I wonder if the species concerned differ in claw morphology from other nuthatches. So far as I can tell this hasn’t been studied. Nuthatches have, incidentally, occasionally been used as examplar ‘tree-climbing birds’ in studies of claw curvature (e.g., Glen & Bennett 2007, Dececchi & Larsson 2012).

“Like a miniature woodpecker”

Nuthatches are something like miniature woodpeckers – well, passerines that convergently mimic woodpeckers, anyway. Nuthatches are, in fact, strikingly woodpecker-like in those details of cranial musculature associated with shock-absorption (Spring 1965) (specifically, the protractor muscles that attach to the interorbital septum are gigantic). They climb with their very robust legs and feet: they don’t have a specialised prop-like tail, as do woodpeckers and trunk-climbing passerines like woodcreepers and treecreepers. Amazingly, they actually move via short hops even when climbing on vertical substrates (Fujita et al. 2008) and are famously adept at ‘head downwards’ climbing. Nuthatches have a well-known habit of storing nuts, seeds and even snails and insects in cache sites that include cracks in tree bark, hollows beneath stones on the ground, or cavities in trees, soil or rock piles.

I’ve found several nut storage sites over the years and have always assumed that they were created by Great spotted woodpeckers Dendrocopos major. Am I right, or could they have been created by nuthatches? One of them was right next to a nuthatch’s regular singing spot (compelling circumstantial evidence), and... look at the photo below showing the Red-breasted nuthatch inspecting a small hole in a tree. Having mentioned woodpeckers, I should say that certain woodpecker and nuthatch species are mortal enemies, competing for the same nest cavities, and reacting aggressively to one another at feeding and nesting sites. The Great spotted woodpecker is also an apparently significant predator of nuthatch nestlings. Nuthatches use mud to reduce the size of the nest entrance, and this helps prevent woodpeckers from entering – and other predators like martens and squirrels, of course (Wesołowski & Rowiński 2004).

Incidentally, the fact that some woodpeckers and nuthatches are so similar in generalities of lifestyle and appearance raises interesting questions about their evolution and history of co-occurrence. Shouldn’t the presence of one of these groups have ‘prevented’ the evolution of the other? Evidently this didn’t happen, so it is that there’s enough ‘ecospace’ for everyone? Or are they mostly avoiding competition in some important way? Well, some studies have found a surprising amount of overlap in bill size, foraging ecology and diet between sympatric nuthatch and woodpecker species (Willson 1971). This wouldn’t happen if these were species invented for a speculative evolution project, ha ha (I kid, I kid).

Nuthatch facts: tool use, colonial nesting, ‘new’ species

As always with groups of animals, there are various interesting ecological and behavioural snippets that tend to get mentioned in every bit of relevant literature, and I’d be letting the side down if I didn’t mention them again. One interesting thing about nuthatches is that several of them are (relatively speaking) only recently discovered. The Corsican nuthatch S. whiteheadi – wholly endemic to Corsica – was discovered in 1883, quite a big deal for a bird endemic to Europe, and the Algerian or Kabylie nuthatch S. ledanti caused an ornithological sensation when discovered in 1975. Since its discovery, additional populations have been discovered (one in 1989 and two more in 1990), but all are in close proximity in north-eastern Algeria.

Also worth noting is that the Western rock nuthatch S. neumayer (of eastern Europe and the Middle East) and Eastern rock nuthatch S. tephronata (of the Middle East and central Asia) were only reliably distinguished in the places where they overlap in the 1920s. Since then, there’s been substantial interest in the idea that these two avoid competing via the evolution of distinct bill shapes and sizes – that is, that character displacement or competitive exclusion is in effect (Vaurie 1951). However, those different bill shapes might be nothing to do with displacement or competition at all but, rather, be reflective of a size cline present across the populations concerned (Grant 1972).

Ten additional ‘new’ nuthatches named during the 20th century from Iraq (S. kurdistanica Ticehurst, 1923), Azerbaijan (S. armeniaca Vorob’ev, 1934), Afghanistan (S. subcaeruleus Meinertzhagen, 1938) and Iran (including S. obscura Zarudnyj & Loudon, 1905 and S. plumbea Koelz, 1950) – this list is far from complete! – are now regarded as junior synonyms of either S. neumayer or S. tephronata (Mlíkovský 2007). There’s also the mystery concerning the Long-billed nuthatch S. longirostris – a species based on 18th century paintings produced in Calcutta and suggested variously to depict an extinct tropical Asian species or rock nuthatches from the Zagros Mountains.

The tiny, endemic ranges of some of the species mentioned here are typical for quite a few nuthatches. They seem to be relicts, clinging to small patches of coniferous woodland (often at altitude) and hemmed in by habitat loss. Not all nuthatches are like this though. The Red-breasted nuthatch S. canadensis is an irrupting species that occurs across much of North America, undertakes regular migrations and has even crossed the Atlantic on occasion. An individual that landed in Norfolk, England, in 1989 – and resulted in a mass invasion of twitchers – lived there for about seven months before disappearing in May 1990 (Aley & Aley 1995). [Adjacent photo by Walter Siegmund.]

The North American Brown-headed nuthatch S. pusilla is of special interest in being a regular tool-user. It uses a scale pulled from pine bark as a foraging tool allowing the removal of additional bark, sometimes carrying the tool with it as it moves from tree to tree. Also interesting is the colonial roosting habit of the highly social Pygmy nuthatch S. pygmaea: as many as 167 have been recorded packed together in the same tree cavity (Sydeman & Güntert 1983).

An interesting question is whether the birds cling to the sides of the cavity in such huddles, or whether they actually stand on top of one another. I favour the latter explanation as this is what nuthatches will do in captivity; it also appears impossible that they could fit into the cavities concerned unless they were literally packed against, and on top of, one another. Do birds ever suffocate or get crushed in such mass huddles? Knorr (1957) reported cases where, respectively, 9 and 13 dead Pygmy nuthatches were found together in the same roosting holes. These probably represent individuals that were crushed to death while packed in the cavity (though maybe some died for other reasons). You might have heard about similar roosting huddles reported for Eurasian wrens Troglodytes troglodytes. In one case, 63 birds were sleeping together in the same one nestbox.

The bit at the end about burning frustration

The aim of this article was to discuss nuthatches (and other sittids: the Salpornis spotted-creepers) within the context of the relevant passerine clade as a whole (Certhioidea), and to cover wallcreepers and treecreepers as well. Oh well, next time. Suffice to say for now that phylogeny indicates that Asia was the place where most of nuthatch evolution occurred (Pasquet et al. 2014). Also seems that I really need to get hold of Erik Matthysen’s 1998 book The Nuthatches. Hey, it's my birthday soon... though I am kinda running out of book-space.

More passerines here in time. For previous Tet Zoo articles on passerines, see...

Refs - -

Aley, J. & Aley, R. 1995. Red-breasted nuthatch in Norfolk: new to Britain and Ireland. British Birds 883: 150-153.

Birn-Jeffery, A. V., Miller, C. E., Naish, D., Rayfield, E. J., Hone, D. W. E. 2012. Pedal claw curvature in birds, lizards and Mesozoic dinosaurs – complicated categories and compensating for mass-specific and phylogenetic control. PLoS ONE 7(12): e50555. doi:10.1371/journal.pone.0050555

Dececchi, T. A. & Larsson, H.C. E. 2011. Assessing arboreal adaptations of bird antecedents: testing the ecological setting of the origin of the avian flight stroke. PLoS ONE 6(8): e22292. e22292. doi:10.1371/journal.pone.0022292

Dickinson, E. C. 2006. Systematic notes on Asian birds. 62. A preliminary review of the Sittidae. Zoologische Mededelingen Leiden 80-5 (14), 225-240.

Enokksson, B. 1993. Nuthatch Sitta europaea. In Gibbons, D. W., Reid, J. B. & Chapman, R. A. (eds) The New Atlas of Breeding Birds. T & A D Poyser, London, pp. 376-377.

Fujita, M., Kawakami, K., Moriguchi, S. & Higuchi, H. 2008. Locomotion of the Eurasian nuthatch on vertical and horizontal substrates. Journal of Zoology 274, 357-366.

Glen, C. L. & Bennett, M. B. 2007. Foraging modes of Mesozoic birds and non-avian theropods. Current Biology 17, 911-912.

Grant, P. R. 1975. The classical case of character displacement. Evolutionary Biology 8, 237-337.

Knorr, O. A. 1957. Communal roosting of the Pygmy nuthatch. Condor 59, 398.

Mlíkovský, J. 2007. Type specimens and type localities of Rock Nuthatches of the Sitta neumayer species complex (Aves: Sittidae). Journal of the National Museum (Prague), Natural History Series 176, 91-115.

Pasquet, E., Barker, F. K., Martens, J., Tillier, A., Cruaud, C. & Cibois, A. 2014. Evolution within the nuthatches (Sittidae: Aves, Passeriformes): molecular phylogeny, biogeography, and ecological perspectives. Journal für Ornithology 155, 755-765.

Spring, L. W. 1965. Climbing and pecking adaptations in some North American woodpeckers. Condor 67, 457-488.

Sydeman, W. J. & Güntert, M. 1983. Winter communal roosting in the Pygmy nuthatch. Paper presented at Snag Habitat Management Symposium. Northern Arizona University, Flagstaff, Arizona, June 7-9, 1983, pp. 121-124.

Vaurie, C. 1951. Adaptive differences between two sympatric species of nuthatches (Sitta). Proceedings of the International Ornithological Congress 10, 163-166.

Wesołowski, T. & Rowiński, P. 2004. Breeding behaviour of Nuthatch Sitta europaea in relation to natural hole attributes in a primeval forest: Capsule Nuthatches used holes with strong walls, typically in live trees with entrances reduced by plastering, and ‘oversized’ interiors filled with bark flakes. Bird Study 51, 143-155.

Willson, M. F. 1971. A note on foraging overlap in winter birds of deciduous woods. Condor 73, 480-481.