Nocturnal Raptorwatching

As time permits, I’ve been reading Don Scott’s The Hen Harrier: In the Shadow of the Slemish, a very accessible book about the author’s studies of Hen Harrier Circus cyaneus in Northern Ireland.  While many experts no longer consider the eurasian Hen Harrier to be conspecific with our Northern Harrier C. hudsonius (most published sources on this side of the moat still regard it a subspecies of C. cyaneus, but see: Simmons 2000), I think the book would be enjoyed by most North American readers.  While the author often comes back to the topic of harrier pairs tree nesting in Sitka spruce Picea sitchensis stands in County Antrim, which is remarkable in itself, I found myself intrigued by the supporting evidence he offered that Hen Harrier might also hunt nocturnally.  The owl-like “facial disk” most harrier species are known for suddenly seems to take on a literal significance.

 

It’s not news to many of you that many “diurnal” raptor species have been observed migrating well after nightfall.  Osprey, in particular, are renowned for making nocturnal journeys even over the Gulf of Mexico.  Northern Harrier and Peregrine Falcon are also known to be nocturnal transients with some regularity.  And, drawing from my own experience, an evening “moonwatching” party with colleagues overseas last September proved particularly fruitful when we observed a Common Kestrel Falco tinnunculus and a Montagu’s/Pallid Harrier(*1) flutter purposefully southbound somewhere between us and a nearly full moon.  We were astonished.  In any case, it’s probably not surprising that the nocturnal habits of many of our diurnal raptor species are not particularly well-studied, and I can’t help but feel that the nocturnal ecology even in our own backyards is almost as much a frontier for field ornithology in some respects as any exotic locale in the world.  (*1: It is not always possible to reliably separate Montagu’s Harrier C.  pygargus and Pallid Harrier C. macrourus in the field.  Even in broad daylight.)

Partly inspired by my experience overseas, and to try to work with (rather than against) a sleeping rhythm “disorder” I’ve had for much of my life, I decided to see how I could leverage my nocturnal proclivities and enjoy birdwatching at times of day when most people are tucked in their beds, drooling into a pillow.  This really isn’t as insane as it probably sounds.  Apart from owls, songbirds migrate predominantly at night, and the nightjars and many seabird species are known to be far livelier when the sun is far below the horizon than when it is above it.  Granted, you can’t use many of the same strategies for watching/counting birds at night that you can in daytime, but there’s still an awful lot you can do!  A neat first step into the realm of nocturnal birdwatching is to leverage the pioneering work in bioacoustics done by the Cornell Lab of Ornithology and build yourself a simple microphone in a re-purposed flowerpot, using it to listen to the call “signatures” of migrating songbirds.  During peak periods, this can be a great deal of fun; and it can also be very humbling, as you soon realize how many birds are flying over your head that you can’t easily put a name to (zeep?).  But put up a pot of tea and give it a spin, listening to the microphone "live" using a pair of headphones while relaxing in bed or your favorite easy-chair.  It’s a surprisingly nice way to “kill” an evening!

My second-hand Baigish 6 NV binocular.  It's lighter than it looks!

But for me, the vintage Russian military GEN2 nightvision unit that arrived in the mail two weeks ago might be the real "game changer."  Nightvision units (sometimes erroneously called “starlight scopes," and not to be confused with thermal imagers) are highly sensitive optical instruments designed to greatly amplify low levels of ambient lighting, enabling you to effectively “see in the dark.”  Looking through an old nightvision (NV) binocular is not like looking through a good daytime binocular.  If you’ve ever seen Gulf War-era news footage of Baghad airstrikes at night (a grim recall, sorry about that!), then you already have a pretty good idea of what to expect: the view through these is grainy, starkly monochromatic with a tendency toward oversaturation, and virtually absent of color apart from a green cast.  NV technology has advanced a lot in twenty years, but for someone new to nocturnal birding with not a lot of discretionary income for these kinds of purchases, even a Soviet-era design opens up an entirely new world!  While animals still have the firm advantage at night, any NV unit kicks wildlife observation up a few notches: surveying a pond at night, you can see sleeping ducks, swimming muskrats, and you stand a good chance of detecting whatever else might be asleep or poking about near the water's edge.  If you know a couple common roosting areas for vultures in daytime, this is a good way to find out how many might be staying the night.  If you’re visiting local grassland preserves (as I plan to be doing this week) you now have the capability to check whether the wintering Northern Harrier reported earlier in the day are hunting nocturnally as you make your rounds.  (I'll definitely report back should I observe this!)  There are a lot of possibilities, although if it isn't apparent by now, NV is no panacea; it has very definite strengths and weaknesses.

I’ll also mention that when I go birdwatching in the evening, I now usually bring my NV unit and my normal daytime 7X binocular.  The reason is that most daytime binoculars are not only superior to NV units in terms of magnification, field of view, resolution, and (most obviously) color rendition, but they still “capture” more light than the naked eye and therefore often yield better views in the dark than you might expect.  Using the two binoculars in turns can be surprisingly effective: use your daytime glass to take in everything that you are able to see of your surroundings, then use the NV unit to fill in the remaining “dark spaces” that you couldn’t resolve with your day glass.  With snow on the ground, when under bright moonlight, or under overcast skies reflecting light pollution from a nearby town (or any combination of these three!), the utility of having both glasses only improves.

In closing, a good day of raptorwatching doesn't have to end.  At all.  In fact, with a good NV glass, when you decide to stop watching raptors is now entirely up to you (or at least up to your internal clock).  I suspect the real "trick" behind nocturnal raptorwatching (and nocturnal birdwatching, generally) is simply breaking out of diurnal thinking that tends to preclude curiosity about nocturnal bird behavior.  Where feasible, try to borrow methodology and utilize technological advances from other disciplines.  If nothing else, you now have even more excuse to make mischief all hours of the day.

Good Hawkwatching,
Arthur

Literature Cited

Scott D.  2010.  The Hen Harrier: In the Shadow of the Slemish.  Whittles Publishing.

Simmons R.  2000.  Harriers of the World: Their Behaviour and Ecology.  Oxford University Press.