The Common Buzzard Buteo buteo and the Red-tailed Hawk Buteo jamaicensis are both their respective regions’ commonest ‘buteos’ and are obviously closely-related, but - in theory - they should never meet: B. buteo breeds (in various forms) right across Eurasia while B. jamaicensis is equally widespread but is found across the other side of the Atlantic. What though if - some would say ‘when’ - one or the other wanders well outside their normal ranges and turns up in front of birders in the ‘wrong’ part of the world?

I’ve been fortunate enough to have seen literally hundreds of both species - I’ve seen Red-taileds all over North America and the Common Buzzard breeds near to where I live and I see one every time I go birding - but I’m still not sure I could definitely correctly identify an anomolous vagrant. ‘Typically’ plumaged birds are different from each other in that - as the name suggests - Red-taileds have more or less unmarked red tails (as adults anyway) and Common Buzzards don’t - their’s are barred. (Having said that the vulpinus or ‘Steppe’ form of Common Buzzard often shows a pale, reddish tail but that’s outside the scope of this short post…)

Common Buzzard, Wiltshire, UK. October 2008.

Red-tailed Hawk, Panoche Valley, California. January 2007

Bearing in mind that these birds are immensely variable across their whole ranges, and that even breeding pairs are often dissimilarly coloured anyway, it’s not really possible to say that the two birds above are really ‘typical’ - or indeed that any vagrants would be adults and look like these strongly-marked individuals. I think they’d be extremely difficult to identify in poor views or if seen in less than ideal weather conditions.

If plumage is not a totally reliable way of separating the two species, how do the average measurements compare? The Common Buzzard is supposedly slightly smaller and shorter-winged than the Red-tailed, but look at how the figures given in eg two leading bird books and on the internet overlap:

• Common Buzzard:
  Length 46 - 58 cm, wingspan 110 - 132 cm. (Collins Bird Guide)
  Length 50 - 57 cm, wingspan 113 -128 cm. (http://www.bbc.co.uk/nature/wildfacts/factfiles/241.shtml)
  Length n/a, wingspan 100 - 130 cm. (http://www.wildlifebritain.com/commonbuzzard.php)
• Red-tailed Hawk:
  Length 48 cm, wingspan 124 cm (North American Bird Guide - David Sibley)
  Length 43-64 cm, wingspan 120 - 150 cm (http://www.pauldfrost.co.uk/redtail.html)
  Length 56 cm, wingspan 142 cm (http://www.desertusa.com/aug96/du_hawk.html)

Factor in that female raptors are larger than males, adults larger than immatures, wingspans vary when the birds are moulting or re-growing the primaries and the situation becomes even trickier.

Red-tailed Hawk, Panoche Valley, California. January 2007

Another ID feature that’s often mentioned is that Red-taileds have a very distinctive wing shape, with a more significant secondary bulge (see photo above) and a narrow, longer fingered hand than Common Buzzard. In excellent views (and with comparative experience) the ‘bulge’ is generally a good ID pointer: in both the photos above the Red-tailed Hawk’s wing is more ‘bulging’, and I’ve other photos which show the same effect. How about though if we see the birds in gliding or flapping flight rather than soaring?

Common Buzzard, Wiltshire, UK. October 2008.

Red-tailed Hawk, Panoche Valley, California. January 2007

You’d have to be a very brave birder indeed to suddenly shout out that you’d just seen a vagrant ….. (fill in the gap depending on where you live)!

So how can you 100% separate both species if they’re not seen in absolutely ideal conditions? I’ve no absolutely certain ideas to be honest, and I’d welcome any comments from any birders who’ve really studied the differences between the two species and could definitely separate extra-limital birds in the field. Maybe one answer is that I should start really studying them in the future…especially if I get as clear views as I was able to get here in the UK this morning on a rare day that the sun was shining and (for once) a Common Buzzard decided to fly right over my head…

Common Buzzard, Wiltshire, UK. October 2008.