Towards UV birding (1 Viewer)

[opisska]

About a half a year ago we had a discussion (in a random thread about Costa Rica birds) about UV photography/observation. I have not yet photographed a bird in UV, but today we have at least proven the concept that we have a near-UV sensitive device in the form of an astronomical CCD camera with the Johnson U filter. We have just patched up what we had in hand, so the result is not very user-friendly - I guess it would be hard to find a bird willing to sit put for the 20 minutes needed to adjust and focus it - but on the other hand with a Newtonian reflector, we had absolutely no absorbing elements, so we got the maximum possible light output. The CCD camera is generally useless for daytime photos because it doesn't really do less than 0.1 s exposures (you can set them, but it doesn't physically move that fast), but in U, even with the reflector setup, there is almost too little light at the 0.1 s.

By taking a photo of my wife's legs with patterns drawn on them with sunscreen, we have proven that we are actually getting some near-UV (and that the filter is actually U, we were not sure). On a test photo in B filter, there is a hint of the patterns, but sufficiently dim. In V,R and I it's all overexposed even when covering the aperture to super small sizes. Other illustrations show the setup - we could not focus to less than roughly 50 meters, so the studio was large. The camera takes about 50W (with cooling, that we could probably have turned off), so it needs a bit of a solar power plant to be used for extended times.

 

[Ted Y.]

Can birds see in UV spectrum?

 

[opisska]

Can birds see in UV spectrum?

Yes. Some species are reportedly quite colorful in UV and as far as I know it serves a purpose as other see that.

 

[THE_FERN]

E g. Kestrels can see UV-reflecting trails of voles' urine iirc

 

[jurek]

Any follow up about birds?

A good trial could be to chat with a local natural history museum curator and photo a number of bird skins, especially birds which are dull to human eye. Actually, the curator could write a cool scientific paper about it.

I am a bit pessimistic here, because I read that UV color in birds enhances color patterns which are already bright or glossy to human eye. So e.g. a male Bluetit and a male Starling have UV-reflecting patches. But never heard that a drab brown tinamou or a warbler will suddenly shine brightly in the forest if one can detect UV.

Curiously, on a recent trip a particular, slightly shiny grey stretching t-shirt scared birds in the rainforest understory. Maybe it was reflecting UV?

 

[Will K]

There’s a David Attenborough programme where they film the blue tit with a UV camera. It’s from The Life of Birds, but I can’t remember which episode it is.

 

[Lerxst]

Any follow up about birds?

A good trial could be to chat with a local natural history museum curator and photo a number of bird skins, especially birds which are dull to human eye. Actually, the curator could write a cool scientific paper about it.

I am a bit pessimistic here, because I read that UV color in birds enhances color patterns which are already bright or glossy to human eye. So e.g. a male Bluetit and a male Starling have UV-reflecting patches. But never heard that a drab brown tinamou or a warbler will suddenly shine brightly in the forest if one can detect UV.

Curiously, on a recent trip a particular, slightly shiny grey stretching t-shirt scared birds in the rainforest understory. Maybe it was reflecting UV?

This study found almost 92% of seemingly non-dimorphic species sampled could be discriminated based on the wider spectral sensitivity of avian vision compared to human. No detail on just how striking this might all look if we were to augment our vision, though.

Avian Visual Perspective on Plumage Coloration Confirms Rarity of Sexually Monochromatic North American Passerines

Abstract. Male and female birds can exhibit striking differences in morphology (dimorphism), including exaggerated plumage structures, size differences, and fea

academic.oup.com

 

[Richard D]

Curiously, on a recent trip a particular, slightly shiny grey stretching t-shirt scared birds in the rainforest understory. Maybe it was reflecting UV?

It's quite likely - I dimly remember seeing a demonstration of how some clothing wildlife watchers were using to not stand out, reflected so much UV it could have been as 'here I am' rather than camoflage.

 

[opisska]

This is harder to bring into something practical then it seemed. The demonstration worked fine, but making a setup that would be practical got kinda stuck.

 

[Richard D]

This is harder to bring into something practical then it seemed. The demonstration worked fine, but making a setup that would be practical got kinda stuck.

Recording into the infrared spectrum is relatively straightforward - UV is a lot harder!

 

[THE_FERN]

I thought many digital SLRs had filters in front of the sensors to prevent UV registering. So you just remove the filter..?

 

[KenM]

E g. Kestrels can see UV-reflecting trails of voles' urine iirc

….During the 1950’s over the midlands, a commercial pilot observed a Kestrel hovering at c11,000’….doing just that apparently.😮

 

[Will K]

I guess you can spend a fortune on binoculars with the best glass and every gadget on the market and still not come close to the viewing power of birds themselves. Science still has a long way to go.

 

[Richard D]

I thought many digital SLRs had filters in front of the sensors to prevent UV registering. So you just remove the filter..?

I don't know about UV, but I had a Lumix GM1 cheaply converted for IR with the removal of the filter.

 

[opisska]

I thought many digital SLRs had filters in front of the sensors to prevent UV registering. So you just remove the filter..?

"Just" removing the filter actually needs quite a bit of skill (and basically totals the camera anyway). The next problem is though the lens, most lenses are very bad at transmitting in UV. I have a couple of lenses measured in lab, the fall-off is very steep around 370 nm usually. That's why something mirror-based would be better, most still have lens correctors - the photos in the first post are made through a Newtonian telescope, mirrors only but getting that at a short enough focal length is tricky.