Vancouver Avian Research Centre

.....Research - Conservation - Education

June - The transition from spring to the summer season was heralded at the end of May with the capture of our first hatch year birds of 2011 when we banded a number of fledgling House Finches. They were aged as hatch year (HY) birds as although they were in full juvenal plumage they were capable of sustained flight and could well have fledged anywhere in the surrounding area.

Conversely this fledgling House Finch was one of five aged local (L) because their juvenal plumage was not yet fully developed, they were incapable of sustained flight, and they were still being cared for by adults.

We always give banding priority to dependent young like this and/or to adults (especially females) that may be caring for young or incubating eggs. Not only do we band and process these birds first upon returning to the banding Pagoda from making our net rounds, but we return them to the site of capture as soon as possible after processing.

This is especially the case with retrapped females with edematous brood patches (see below) where we will often record the band number at the net and release them on the spot after extraction. 

The breeding season is a particularly advantageous time for banders because sex-specific physiological changes in many species can allow otherwise unknown sex birds to be designated as either male or female.

As most birders and banders know, many species are sexually dimorphic meaning we can sex the bird based on characteristics such as plumage coloration and/or size. However many species are sexually monomorphic meaning both females and males look exactly alike and these species can only be sexed in the hand in spring and summer when they show breeding characteristics i.e. a cloacal protuberance (CP) or a brood patch (BP).

In many monomorphic species, the male's cloaca becomes enlarged and bulbous during the breeding season, the base narrow and tip swollen (as in the photo below left), the purpose being to store sperm and aid with copulation. This is called a cloacal protuberance, or CP. The swelling of a male's cloaca develops gradually and is not always as obvious as this fully developed CP on a male Song Sparrow but can be identified with experience.

Female passerines on the other hand conduct most if not all of the incubation and develop brood patches (BP). At this time they will lose the feathers on the breast and belly to facilitate direct skin contact and maximum heat transfer to the eggs for incubation.

The photo below right shows a fully developed brood patch with wrinkled and highly vascularized skin. The development of the brood patch progresses in stages similar to the development of the cloacal protuberance of the male, the feathers of the breast and belly are first shed and the blood vessels under the skin increase in size and number until the brood patch is edematous (i.e. highly vascularized and swollen) such as in the photo below right of a female Purple Finch with a fully developed brood patch.

The result of all this breeding activity is of course baby birds and we couldn't resist the opportunity to show a couple  more photos of birds in juvenal plumage (Dark-eyed Junco below left and American Robin below right) both scoring 10s on the cuteness scale!

Last month we looked at two similar Empids in the hand, Dusky and Hammond's Flycatchers - this month we were tested with another one! Our common Empid is Willow Flycatcher (photo below right) which breed in large numbers in the park, their distinctive "fitz-bew" songs resonating seemingly from every bush - the bird below left had us puzzled and our immediate thought was Alder Flycatcher!

Willow (WIFL) and Alder (ALFL) Flycatchers together form 'Traill's' Flycatcher, our largest Empid, are virtually identical and were actually considered the same species until the 1970's. ALFL breeds across northern BC and WIFL across southern BC without significant hybridization, both species breeding in wet thickets and shrubby areas such as we have at Colony Farm.

Looking at the two birds below there were a number of subtle differences which had us leaning towards ALFL. The first was the much lighter lores of the possible ALFL compared to the WIFL without conspicuous light-coloured lores. The second was the dorsal plumage being somewhat greenish above compared to WIFL which is greyer above. The third was the wing bars and tertial edgings of the presumed ALFL which were slightly broader and brighter than the WIFL and there was definitely a sense of more of an eyering which is lacking on WIFL. One thing that didn't agree was crown spotting which in the ALFL should be larger and more distinct although adult crowns are more spotted than first year birds and males more than females.
Finally notice the size of the bill on the possible ALFL - although this is not a factor to separate ALFL from WIFL the bill was absolutely huge and reminded us more of the bill proportions on a Tropical Kingbird rather than an Empid!

We looked at wing morphology and determined that primary 6 (P6 below left) was not emarginated (i.e. there was no indentation on the outer web) which at least ruled out it being any other Empid as Traill's (WIFL/ALFL) are the only Empids where P6 is not emarginated!
The bird was aged as an after hatch year (AHY) of unknown sex.

The wing (below right) showed the classic 'eccentric' pattern of incomplete molt in Tyrant Flycatchers with replaced and retained remiges (primaries and secondaries) this bird clearly showing the difference in rachis (shaft) colour between the retained two innermost primaries (PP1&2) and the replaced outer primaries and inner secondaries. But as much is not known of the molting patterns of this species this replacement pattern could be from the preformative, prebasic or prealternate molts.

We took our other biometric measurements, banded the bird with a size '0' band which is the size for both ALFL and WIFL and recorded species as 'Traill's' Flycatcher with notes as to the likelihood of this silent Empid being an Alder Flycatcher!

Another Empid banded this month was this Pacific-slope Flycatcher (photo below left). Although the Latin name for PSFL is Empidonax difficilis they are probably the least difficult Empid to identify in the hand as the gray leg colour (photo below right) is unique, other Empids having black or blackish legs.

We band a number of Brown-headed Cowbirds each year and are always surprised when visitors give them such a bad rap sometimes saying things like “Don’t you euthanize them?”

We don’t! And actually we think they’re pretty neat birds and try to educate people that the problem with Cowbirds is humans!
 
Originally birds of the open grasslands following cattle herds in search of seeds and disturbed insects Cowbirds evolved to become brood parasites, laying their eggs in the nests of other birds and abandoning their young to foster parents as they continued their nomadic lifestyles.

In the course of a single nesting season, a female cowbird like this one (photo below left) may produce as many as 40 eggs over as many or more days. The challenge for her is she has to find as many nests of potential host species at just the right stage of laying in order for just a few of her offspring to have the chance to survive to independence. This is actually about the same number of young that many cowbird host species themselves will raise in a single season by tending just one or two nests containing four or five eggs each!

The challenge is when cowbird nesting success almost completely eclipses the nesting success of its host species particularly in small forest fragments surrounded by agricultural landscapes. Some of these fragments are large enough to attract forest nesting host species such as Thrushes and in these areas the hosts experience exceptionally heavy cowbird parasitism pressure due to the fact that a very large population of cowbirds is supported by the ever expanding surrounding agricultural landscape. This can cause what is known as a "population sink" meaning the host species may effectively raise only cowbird young but again, the irrefutable negative impact of cowbirds on some host species in such areas is symptomatic of the continuing conversion of forest to agricultural and other land uses by human beings!

Cowbirds are sexually dimorphic, females having pale grey body plumage and brown heads and males having bright glossy black body plumage and rich brown heads. Males do develop cloacal protuberances (CP) but females do not of course develop brood patches.

Females are also considerably smaller than males with shorter wing chords (the length of the unflattened wing) and in fact take a smaller band size.

Cowbirds are members of the Icteridae family and can have complete first and adult prebasic molts although the first prebasic molt is rarely complete with a number of underwing coverts normally retained. The photo on the right shows the left underwing coverts of a second year (SY) male, the red arrow pointing to the darkly pigmented and glossy black replaced coverts.
Although replaced underwing coverts are easy to see on males as in this photo, the contrast between retained and replaced feathers on females is much more difficult to detect and due to this some are impossible to age.

Another first banded species for us was this stunning after hatch year (AHY) male Northern Harrier made all the more unusual as it showed up in one of our woodland nets. We often see NOHAs hunting over the open fields of Colony Farm where there is a large Townsend's vole population but their slow, flapping flight near the ground and keen eyesight makes it easy for them to avoid our nets in these more open areas.

Unlike other raptors Northern Harriers rely on hearing as well as vision to capture prey. The facial disk is much like that of owls, the stiff feathers helping to transmit sound to the ear openings to locate prey.

 

Cedar Waxwings flooded back in to the park this month filling the air with their electric, high-pitched trills as they fly around devouring the ripening Elderberry fruit.
CEDWs are one of our favourite birds and definitely one of the best posers!
The name 'waxwing' comes from the waxy red secretions found on the tips of the flight feathers (primaries, secondaries and retrices). These red waxy appendages are usually restricted to the secondaries, giving a usual maximum of nine wax tips per wing (seven wax tips is by far the commonest number). Rarely, some retrices (tail feathers) will also have the tips of their shafts red.  More rarely still, small red wax tips can be seen on one to a few inner primary wing feathers. Our record was one bird with an impressive grand total of 36 waxy appendages!
The exact function of these tips is not known, but they are age related as is the extent of yellow on the tips of the retrices.
The number and length of waxy tips together with the extent and glossiness of the black patch at the base of the chin allows us to determine sex, the black being brownish black and much less extensive on females and extensive glossy black on males.

This is not only helpful to banders but is also helpful to birders particularly those participating in citizen science projects like the Breeding Bird Atlas as CEDWs can be identified not only to species but also to age and sex using this information. We'll leave it to you to try this out by ageing AND sexing the bird above left (answer is at the end of the blog!)

Cedar Waxwings are true frugivores which specialize in eating fruit and they can survive on fruit alone for several months. We've noticed that when CEDWs first arrive back and the Elderberry fruit isn't ripe they develop hardened, sticky resign at the base of their bills and on their foreheads (photo above right) which the birds are unable to clean off their bills and feathers. Sometimes this hardens to such an extent that feathers are shed, probably due to scratching as the birds try to dislodge the irritating substance and creating extensive bare patches at the base of their bills.

Our Hummingbird monitoring continued in June both at Colony Farm and on Vancouver's north shore. We band both Rufous (RUHU) and Anna's (ANHU) Hummingbirds here in Vancouver and we never cease to be amazed by these tiny birds.

ANHUs are year round and overwinter in Vancouver whereas RUHUs breed as far north as Alaska and overwinter in Mexico. ANHUs are larger than RUHUs, this after hatch year (AHY) female (photos below right) weighing in at 4.3 grams and the after hatch year (AHY) male RUHU (photos below left) weighing in at a mighty 3.3 grams - that's not much more than a Canadian penny which makes their long migrations seem even more impossible with those tiny wings beating at 80 beats per second and hearts beating at something like 1,200 beats per minute in flight!


 

Hummingbirds are Apodiformes which comes from the Greek meaning 'no feet'. They do of course have feet but they are too far back on their bodies to enable them to walk which makes for great photo opportunities with visitors who can marvel at a Hummingbird sitting on their open palm before taking to the air again.

We make the bands for Hummingbirds ourselves from thin sheets of stamped aluminum provided by the federal Bird Banding Laboratory, carefully cutting, filing and forming the bands to the correct size. The finished band is not much larger than the tip of a retractable pencil (photo right) and special pliers are used to attach them to the birds tarsus.

Ageing Hummingbirds is relatively easy as all species can be aged for the first 5 to 9 months after fledging by the extent of grooves called corrugations along the lateral portions of the upper mandible.

When Hummingbirds are born the bill is soft and these deep grooves are easily seen under magnification (photo below left) whereas adult bills are smooth, hard and shiny along the entire length of the upper mandible (photo below right).

This beautiful after second year (ASY) female Evening Grosbeak turned up at our feeders during the month. Although Evening Grosbeaks breed in BC they are  uncommon in the lower mainland and our previous captures have all been in the very early spring. With no evidence of a brood patch and a fat score of 3 (out of a possible maximum of 5) she was almost certainly a transient and after a few days gorging on our sunflower seeds left the banding area and wasn't seen again.

 

Purple Finches (PUFI) breed in large numbers in the park and can be separated from House Finches (HOFI) by looking closely at the culmen (the ridge of the bill from the base of the feathers to the tip) which is straighter in PUFIs and more decurved in HOFIs.
PUFIs have delayed plumage maturation meaning males do not attain their full purple plumage and become what Peterson described as the "sparrow dipped in raspberry juice" until their definitive adult prebasic molt following the breeding season in their second year.
Visitors often say they only have females at their feeders but because of this these birds could actually be either females or young males.
Ageing of this bird was therefore very easy! (answer at the end of the blog!)

PUFIs are also facultative (as opposed to obligate) migrants meaning they may or may not migrate depending not on ambient temperatures but on whether enough food is available on their breeding grounds in a given winter. We know this to be true as we band them during the winter at our nearby Burnaby Lake winter banding station where we operate feeders throughout the winter months.

Another Tyrant Flycatcher showed up this month and had one of our volunteers confused who called it a Willow when he brought it back to the banding Pagoda.

Like Willow Flycatcher P6 is not emarginated and there is no eyering on this flycatcher but the dark vest is very different from any Empid as are the smudged undertail coverts. This flycatcher has a very long primary projection and the bill is much longer, the underside being 1/2 to 3/4 dark versus pale on Willow as illustrated in the photo at the beginning of this month's blog.
 
Finally the wing tips of this flycatcher reach to the tips of the undertail coverts (photo below right), on Traill's they are much shorter making this bird a definitive Western Wood-Pewee.

We had another first for the season and couldn't leave this month's blog without a photo of Colony Farm's iconic bird, this absolutely stunning after second year (ASY) male Lazuli Bunting which was a particular treat for John Hague a visiting birder from Yorkshire, England who spent the morning with us and got to see some of Vancouver's birds up close and personal before leaving on his travels around the province. As a Londoner I took a bit of an exception to him calling all English southerners 'softies' and to the fact he supports Sheffield Wednesday football team but apart from that he was really quite a decent bloke! Happy travels and birding John!

Many thanks to Mark Habdas, Kerry Kenwood, Carol Matthews, Dev Manky, Jason Jones, Saskia Wischnewski, Ian Thomas, Greg Schultz, Debbie Wheeler, Celia Chui, Sarah Gray, Eric Demers, Chris and Marguerite Sans, Marianne Dawson and Gabriel Jamie visiting bander from Cambridge University England for their help with banding this month.

ANSWERS:

1. The CEDW above is an adult (After Second Year) male based on the number of waxy appendages, extensive yellow on the retrices and extensive, glossy black base to the chin!

2. The PUFI above is an adult (After Second Year) male

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