Vancouver Avian Research Centre

.....Research - Conservation - Education
Fall (September - October 2014)

Although fall 2014 was spectacular for us for the number of birds banded and species diversity  with a number of new species banded for the station, pride of place in the blog has to go to our Northern Saw-whet Owl monitoring, which, following two previous years in which not a single owl was banded, produced 41 owls and a foreign retrap!

The Saw-whet Owl is one of the smallest owls in North America and is only 7-8 inches from bill to tail although its wingspan of 18-22 inches makes it appear larger in flight. Its small size allows banders to capture them with the same mist net techniques used for passerines.

They are nocturnal owls, hunting mainly at dusk and dawn and roosting in dense conifers during the day relying on the foliage cover and their plumage for camouflage. We have always thought that the mixed coniferous-deciduous wooded edge habitat at the banding station where we operate our 'playback' nets should provide ideal habitat for them and the large vole population at the Farm should provide a plentiful food supply so we were hugely disappointed when our previous monitoring efforts were unsuccessful.

This year turned out to be very different!

Northern Saw-whet Owls begin migrating as deciduous foliage nears peak colour, utilizing habitats along their migration routes that are similar to their breeding habitats, and ends approximately 1 month after leaf fall, thus migration begins during mid-September north of 45 degrees north latitude.

Monitoring is conducted from dusk until dawn (if you can stay awake that long!) using an array of nets with an audio lure placed at the junction of the central nets with net checks conducted each hour during the night. This means many hours of sitting around in the cold and dark trying to keep warm and telling jokes and mindless stories to stave of the boredom! (You actually find a lot out about people when you're owling with them!)

But as the following photographs show it's all worth it when net rounds produce owls!

And following a unanimous vote by all staff and volunteers we can categorically say that Northern Saw-whet Owls are by far the cutest birds on the planet!

Each bird is placed in to a soft straitjacket (above) while they are being processed - this ensures careful handling and allows us to carefully check heavily feathered legs; to be certain that the right band size is used and to feel both legs to verify that the owl is not already banded.

Unlike passerines the structure of the toes is different in owls as the outer front toe (digit 4) on each foot can be swiveled to face the rear (a configuration termed Zygodactyl). When in flight, 3 toes (digits 2, 3 and 4) face forward, and one (digit 1) backwards but when perched, or clutching prey, the outer toe (digit 4) swivels to face the rear.

The combination of this toe configuration, needle sharp claws and nobbly protuberances on the underside of the feet all help owls to grip prey.

Hearing, of course, ranks high in its importance to birds and their survival.  The ear openings of most birds are hidden under feathers and only visible on a bird in the hand.
Owls' hearing is particularly acute because many hunt by sound alone.  They have, therefore, many unique adaptations.  The ears on many owls, for one, are asymmetrically arranged on the sides of the head, that is, one is usually higher on the head than the other and they are often shaped differently, this helping to locate prey and calculate its exact location.
Also, in front of the ear on both sides of all owls, is a movable skin fold that no other group of birds has.  Its purpose, to reflect and concentrate sound waves coming from behind.

Another adaptation for silent hunting at night are the comb like serrations on the leading edge of the primaries (red arrow) which distribute air rushing over the wing into small vortices, thereby reducing turbulence and noise.

Ageing and sexing Northern Saw-whet Owls is relatively easy. Hatch year (HY) birds do not replace remiges (primaries and secondaries) in their preformative molt and therefore, as in the bird above, all primaries and secondaries are a uniform shade of brown.

This is even easier to see under Ultraviolet light, as the porphyrin in the feathers glows pink across the entire underside of the wing.

A second year (SY) bird replaces the outer primaries and inner secondaries after its first breeding season. These replaced feathers contrast visibly with the retained inner primaries and outer secondaries and again, the new feathers glow pink while the older feathers are washed out and bluish under ultraviolet light.

After second year (ASY) birds show a pattern of mixed new, one-year old and two-year old feathers. 

Third year (TY) birds like the bird below show an increasingly fragmented pattern with 3 distinct generations of feathers and after third year (ATY) and fourth year (4Y) birds show complex patterns in which 4 generations of feathers can possibly be identified.

As female Northern Saw-whet owls are generally heavier and have longer wings than males, sexing birds is also relatively easy using a combination of body mass and wing chord to determine sex.

And if ageing and sexing owls doesn't really interest you, then just enjoy these stunning little birds for the miracles of nature they are!

So Northern Saw-whets took center stage but they weren't the only stars of the show this fall as we banded a number of rare and/or uncommon species including several which were firsts for the station.

This hatch year (HY) male American Redstart was not only new for the station but also a first record for Colony Farm.

Vagrant birds are exciting for birders and banders alike but they also have scientific value. Long term data sets may provide evidence for historic changes in population sizes and understanding the patterns of such occurrences is important in increasing our knowledge of dispersal of species. These long range dispersal events may also be critical for the survival of many species in the face of the anthropogenic climate changes we are seeing.

The preformative molt in American Redstart includes all medium and greater coverts and greater alula covert (A1), the molt limits shown with red arrows below between the outer greater covert and inner primary covert and between the greater alula covert (A1) and lower main alula feather (A2). Notice the contrast between the fresher replaced greater coverts and washed out, lightly pigmented and more abraded primary coverts and lower alula feathers.

Tail shape is helpful in ageing many species being tapered and more abraded on retained juvenal feathers in first year birds (HY/SY) and broad and truncate with a corner to the inner web and relatively fresh in adults (AHY/ASY). The outer retrices (R4-R6) generally show the greatest age specific differences.

As mentioned in previous blogs, the fact that tail feathers are frequently lost and replaced between normal molts tail feather shape must be used with great caution by banders, and only with other supporting characters (e.g., molt limits), when determining the ages of birds in hand.

The tail of the bird above is showing very tapered rectrices and young males like this bird show an extensive yellow patch on R3 (red arrow) which is reduced or lacking in young females.

Another first for the station was this hatch year (HY) Clay-colored Sparrow, a rare transient for us here on the coast.

The preformative molt in Clay-colored Sparrow usually includes all median and greater coverts, but this bird had replaced only median coverts (red arrow) but not greater coverts. Notice also the narrow, tapered and abraded retained primary coverts and alula contrasting with the darker centred replaced median coverts.

Although sometimes central rectrices can be replaced in the preformative molt, the tail of this bird was showing all retained, tapered and relatively abraded rectrices.

Another example of rare transients are the regular occurrences of Northern Waterthrush each fall in the park. This rare transient in the Vancouver area is becoming an expected capture for us at this time of the year and the 2014 season saw multiple captures.

Northern Waterthrushes are not thrushes of course but one of the larger, terrestrial wood warblers which spend most of their time walking on the ground.

Ageing Northern Waterthrushes in the summer and fall is relatively easy as juveniles typically have narrow rusty tips to the tertials (red arrows) and narrow, more tapered rectrices.

White-throated Sparrows were also unusually abundant during the 2014 fall season with multiple captures and sightings on some days.

The high insect, seed and fruit production in the park in the fall provides an ideal environment for migrant birds to deposit fat to fuel the energy demands of long distance migrations. Although White-throated Sparrows eat mainly seeds of grasses and weeds this bird had been fattening on the ample supply of elderberry fruit in the park.

And completing other firsts for the station was one of two Belted Kingfishers.

We talked above about the configuration of toes in owls, in kingfishers, the third and fourth toes are partly fused, an arrangement that is termed syndactyl and likely an adaptation for holding slippery fish and shoveling earth to dig burrows.
 

A sure sign that winter is on it's way and that our main banding season has finished for another year is the arrival of the first Northern Shrikes in the park.

Northern Shrikes breed much further north in the taiga and tundra and some overwinter in the park. Hatch year (HY) birds like this one are more brownish overall than adults with prominent molt limits in the greater coverts (red arrow) and have distinct barring on the chest and less distinct face masks.

Northern Shrikes which although such stunning birds are probably our most aggressive species in the hand with lethally hooked bills easily capable of drawing blood. Even Ivand who had no qualms scaling 50 foot ladders to help catch Cliff Swallows in the summer decided to don the gloves for this one!

So, that's it for another season for VARC at Colony Farm with record banding effort, record numbers of birds banded and record numbers of visitors to the station.

2015 is already shaping up to be an exiting year with the launch of the World Bird Research portal and the hosting of the Western Bird Banding Association (WBBA) conference  and we look forward to welcoming banders. ringers and other visitors.

A special thank you to Debbie Wheeler for the extraordinary amount of time and effort she has put in to VARC this year both at and away from the station. This included attending just about every banding session, repairing nets, making hundreds of hummingbird bands, entering data and for all the amazing photography including the images above. Thanks so much for all of your hard work Deb - I don't know what we would have done without you!

And finally. as always none of the work we do would be possible without the help of so many people which now seemingly includes a cast of thousands between all of the Friends of VARC, our sponsors and donors, visitors, workshop participants and of course all of the VARC volunteers who sacrifice their weekends and set alarms for unearthly hours during the summer months mostly on their weekends off to help with banding operations - again thank you all!

See you all in spring 2015 - Happy winter banding, ringing and birding wherever you are in the world!

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