Green Backed Rufous Hummingbirds

25 07 2020
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Rufous Hummingbird – Luke Tiller

Rufous vs Allen’s Hummingbird is an age old ID conundrum here in Southern California. While Allen’s Hummingbird are resident year round in Los Angeles, Rufous are just passing migrants whose breeding range barely dips into the very far north of the state. Though they have been seen outside the following window, migrant Rufous are mainly an ID issue for local birders between the first week of February and the end of May and the last week of June through the third week of September. Beyond those times it’s probably relatively safe to assume you are looking at an Allen’s Hummingbird unless you have direct evidence to the contrary.

I think it’s safe to say that if you asked most local birders they’d know that it’s very difficult to identify Rufous and Allen’s Hummingbirds in the field unless you are looking at adult male birds. The common theory goes that most female and juvenile birds are best left unidentified to species during the aforementioned window, but that if you are looking at adult males the orange backed birds are probably Rufous and the green backed ones probably Allen’s.

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Allen’s Hummingbird – Luke Tiller

Though of course I’ve known that around ten percent of adult male Rufous Hummingbirds can be green backed I think I’ve somewhat lazily presumed that one in ten is a low enough percentage that you’re probably fairly safe assuming any green backed adult male Rufous/Allen’s here in Altadena is an Allen’s even during this migration period.

This spring however (2020) was an excellent one for finding Rufous Hummingbirds at one’s feeders. I think cool temps and rain in February and March had stunted blooms and left birds more dependent on feeder set-ups. For some reason our yard has never been that popular with adult male Allen’s Hummingbirds, so when I suddenly started seeing a fair few green backed adult male Rufous/Allen’s coming to the feeders I started getting curious about their true identities.

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Feeder Hummingbirds – Luke Tiller

The only way to truly separate these two species are by looking at individual tail feathers. This is essentially impossible to do without a camera as you need spread views of their tails. I therefore set myself the task of photographing a few of these green backed birds in order to uncover their identities.

Though the outer two tail feathers (retrices four and five) on adult male Rufous Hummingbirds are wider than adult male Allen’s Hummingbirds, the most obvious identifier is retrix two (the tail feather to the right or left of the two central tail feathers) which has a distinct notch on its inner edge, creating a distinctly shaped feather different to the smoothly tapered retrix two (R2) of an Allen’s Hummingbird.

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Allen’s vs Rufous Hummingbird Tail Pattern – Luke Tiller

To my surprise when I started taking spread tail photos of these green backed birds I discovered that many of them were in fact Rufous Hummingbirds. In fact at my feeders I had more green backed Rufous Hummingbirds than I had actual Allen’s Hummingbirds.

To illustrate the point, here are the tail patterns of these two green backed birds in the photo above. First the right hand bird that’s perched in the shot. Following that is a blow up of the above feeder photo. Again showing the distinct tail notch of an adult male Rufous Hummingbird. This bird is even more extensively green backed than the one on the right.

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Rufous Hummingbird with notched R2 – Luke Tiller

After taking these two photographs I’m now convinced that I need to be much more careful about how I enter data into eBird, even when it comes to identifying the supposedly more easily identifiable adult male Rufous/Allen’s Hummingbirds. Every year there are Rufous Hummingbirds that show up outside the typical window, but I think Kimball Garrett’s challenge of photographing an adult male Rufous in midwinter has yet to find a claimant for that prize.

Young male and female birds of all ages are even harder to identify. If you want to do some research into identifying Rufous and Allen’s Hummingbirds, check out Sheri Williamson’s excellent blog post (here). I highly recommend her hummingbird field guide too (here).

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Blow up of above photo. Note notched R2 of Rufous Hummingbird – Luke Tiller


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