Powdermill Banding Fall 2005

Fall 2005

Past Pictorial Highlights
October 4-9

(Guest-authored by visiting British ringer,
Dr. David Norman)

We banded 715 birds of 54 species this week, nearly half of the total coming on Sunday 9 October when the day's banding total of 349 was the 16th biggest day in the 45-year history of Powdermill, compensating for the one-and-a-half days washed out with heavy rain. The rain, although disrupting the banding program, was much-needed as this is only the second time in 45 years that some of Powdermill's ponds have dried out.

Top species this week was Magnolia Warbler, with 59 banded, followed by Gray Catbird and American Goldfinch (52 each), Common Yellowthroat (48) and Ruby-crowned Kinglet (43). Eighteen species of wood warbler (209 birds banded) was exceptional for early October. Other notable totals included 31 Eastern Phoebes and 38 Indigo Buntings. Three new species (actually, two species and a recognisable subspecies) for the fall brought this season's species total (from August) to 100.

This week we thank our volunteers, Pam Ferkett, Brian Jones, Randi Gerrish, Carroll Labarthe, Hanna Mounce, Matt Shumar, and Molly McDermott for their help with the banding and recording.

Apart from enjoying the pleasant atmosphere amongst friendly people, and the glorious fall colors of the Pennsylvanian landscape the main reason that I keep returning to Powdermill is – of course – for the birds, especially their diversity. Coming from a small island (Great Britain) with a limited avifauna, I find the species diversity at Powdermill amazing, bringing many challenges in identification, ageing and sexing. Powdermill, lying 400 miles inland, also receives a relatively high proportion of adult (after-hatching-year) birds, probably close to the true proportion in the population as a whole, rather than the excess of inexperienced hatch-year individuals found at most migration stations at the coast. This well-known ‘coastal effect’ means that some sites see very few adult birds, and some banders working exclusively at coastal stations perhaps do not develop the familiarity with adult plumages that can be seen at Powdermill. Having such a variety of species and ages is good for training banders’ skills in examining plumage, as at last week’s Bander Development Workshop, especially as we get to the end of the ‘skulling season’ when the ossification of many hatch-year birds’ skulls is complete.

Black-throated Blue Warbler males are a good place to start. After hatch year birds have bright blue coverts, alula, and darker wings.

In their first fall prebasic moult, hatch year birds almost always moult all of their lesser, median and greater coverts, and the carpal covert, and also A1, the alula covert, giving an obvious moult limit between the blue-fringed A1 and the green-fringed A2 and A3, the middle and large feathers of the alula. In Powdermill shorthand, this is known as ‘an A1 moult limit’, this being the most commonly adopted pattern for many birds including all of the wood-warblers. The dull quality of the unmoulted primary coverts is also obvious. In workshop discussions I have described the Black-throated Blue Warbler example as ‘Moult limits for Dummies’, taking the name from the famous series of books, because male BTBWs must be amongst the easiest of all species in which to see the difference between the two generations of feathers.

Some Gray-cheeked Thrushes are often almost as easy to age, but here the typical moult limit is within the greater coverts (gcs), many HY birds retaining most of their gcs, as with this bird which has 8 old gcs.

But the retained greater coverts of some Catharus thrushes – perhaps as many as 50% of birds – do not have the light-spotted tips that make an individual like this so easy to determine.

Magnolia Warbler AHY males have black uppertail coverts, and this individual is also easily identified as a male by the black streaks on the flanks, broader than the width of the tarsus, a rule of thumb pointed out more than 40 years ago by Chandler S. Robbins in his famous paper ‘Ageing and Sexing of Wood Warblers (Parulidae) in Fall’ (EBBA News 27: 199-215 (1964)). This should not be the only criterion for sexing, of course, but the breadth of the flank-streaks is very easily noticed during the banding operation. This rule of thumb is also helpful, but not infallible, for sexing Yellow-rumped (Myrtle) Warblers. In most species, wing length can also be helpful in sexing, but there is more overlap in Magnolia Warblers than most species (Relationships among body mass, fat, wing length, age, and sex for 170 species of birds banded at Powdermill Nature Reserve, by Robert S. Mulvihill, Robert C. Leberman and Adrienne J. Leppold, Eastern Bird Banding Association Monograph No. 1, March 2004).

Another technique for ageing some species is to use the tail shape: in my experience, British ringers tend to rely too much on tails for ageing, but American banders probably use them too little! The tail shape can be helpful in ageing Ruby-crowned Kinglets, especially as some of them finish skull pneumatization earlier than many other species, and their moult limit can be difficult to see. Few AHYs have rectrices as obviously broad and truncate as this:

Even so, we have to beware of using the tail shape as the only characteristic for ageing: it is possible that some individuals lose their whole tail accidentally, in which case the newly grown tail would have the ‘adult’ shape. Also, in Britain, where their close relative the Goldcrest Regulus regulus is resident on some of my ringing sites so I have examples of known-age birds ringed two or more years before, many birds do not attain a broad ‘adult-like’ tail. Anyone who wants to know more about the similarities and differences between Ruby-crowned Kinglet, Golden-crowned Kinglet, Firecrest and Goldcrest can see a photo-essay at http://www.merseysiderg.org.uk/, on the ‘bird in the hand’ page for 15 December 2003.

A good supply of adult birds also in many cases allows a thorough study of the process of full prebasic moult. This is one of the main things on which I am working, to produce, with Bob Mulvihill, an analysis of the timing and duration of moult in about fifty of the species recorded in moult at Powdermill. Birds in heavy moult tend not to fly far, certainly not on long migratory journeys, but adult warblers are often caught at Powdermill Nature Reserve as they are coming to the end of their full moult, such as this Black-throated Green Warbler, banded on 25 September 2005 when the last of its moulting feathers – the innermost secondaries and outermost primaries – were still growing.

Many of the long-distance migrants, such as wood-warblers, tend to moult to a rather predictable schedule, owing to their time-pressures of having to fit in a full moult between when they finish caring for their fledgling young and when they set off on their migratory flights. On the other hand, species with a long breeding season, in which some individuals may have two or more breeding attempts, can have a much more extensive moulting period. A good example is the American Goldfinch, and two females caught on 9 October showed extreme differences.

The lower bird in this photograph is moulting about five weeks later than the upper bird, presumably because she has raised an extra brood. The lower bird had only just started moult, its new innermost primary feather having emerged from its sheath perhaps the day before and barely visible, with all other remiges ‘old’, grown in 2004. The other bird, at the top of this photograph, already has all of her new primaries (p1-p5) fully grown, with the outer primaries all growing, and the only ‘old’ remiges left are the innermost secondaries (s4-s6), which will be replaced in the next week or so. All of its lesser, median and greater coverts have already been replaced. Comparing the two birds, the two generations of feathers show large differences in color, mainly from bleaching, and wear, especially of the lighter-colored parts of each feather: this is why most birds need to moult annually.

A more extensive discussion of the variety of moult in American Goldfinches will be provided on a future Powdermill banding website.

For some species, occasionally a bird in heavy moult can look so odd that it is almost unrecognisable. One such example, caught on 5 October 2005, provides this week’s mystery photo.

This bird is an adult (after-hatching-year) Hermit Thrush, a female with a brood patch now feathering over, who also must have had a late brood. Moult made its identification more difficult because of the absence of its longest primary feather, precluding an accurate measurement of wing length, and especially by the complete absence of its tail, just starting to grow but with the feathers not sufficiently emerged from their pins for the rusty color to be seen.

Not surprisingly, some of the birds caught this week were hatch-year birds that appeared to be the products of late breeding attempts. Hatch-year Red-eyed Vireos usually moult all of their greater coverts, but one banded on 9 October had retained five juvenile greater coverts, presumably having fledged late and being unable to undertake the usual extensive first pre-basic moult.

An Indigo Bunting on 9 October was mostly still in juvenal plumage, presumably a very late-hatched bird, and was moulting only a few median coverts. The parents of a bird like this will only recently have started their own full prebasic moult, or could even be delaying it until the winter quarters, as we speculated about a couple of very worn female INBUs in last week's update.

No Powdermill webpage update would be complete without the traditional photo gallery of new species for the fall, and other highlights, of which there were many this week.

This year’s first White-crowned Sparrow was banded on 4 October, a hatch-year bird:

I was pleased on 5 October when we finally caught some real thrushes – American Robins, Turdus migratorius. Some readers will know that all of the north-west European thrushes are big birds of the Turdus genus, not those tiny Catharus birds masquerading under the title ‘thrush’!

The ‘Yellow’ Palm Warbler caught on 6 October was the first at PNR since 16 April 2003, and the first in fall since 7 October 2000.

Whilst the plumage of this hatch-year female might not look convincingly ‘Yellow’ to all observers, we have interesting confirmatory evidence of the race of this bird from another of the Powdermill Avian Research Center’s programs. Mike Lanzone and his team in the bioacoustics lab are recording the ‘chip’ calls made by warblers captured for banding, and their response to playback of calls of their conspecifics and of other species. This ‘Yellow’ Palm Warbler did indeed respond to recordings of Yellow Palm Warblers, and not to those of Western Palm Warblers. Now, there's an identification technique that doesn't feature in the banders' manuals!

This Yellow Palm Warbler is shown in the next image for comparison with a hatching year female Western Palm Warbler featured on the Powdermill bird banding webpage for 18 September 2002.

This HY Northern Parula banded on 6 October taxed our ability to decide upon its sex (being intermediate in wing length and some plumage criteria), with opinion tending towards female, but eventually it was left as ‘U’ (undetermined).

This bird exhibited very little white in its outer tail feathers, indeed invisible in many views.

Not a new species for the fall, following last week’s featured bird, caught on 1 October, but another Orange-crowned Warbler on 6 October left us in no doubt about his sex, especially when helped to splay his crown feathers.

Unlike last week’s individual believed to be of the western race Vermivora celata orestera, this Orange-crowned Warbler appeared to be of the nominate V. c. celata race.

October Northern Waterthrushes are not that common, and seem to have become rarer over the years. We have to go back 14 years, to 1991, to find one banded on a later date than this hatch-year bird, 9 October.

Male Blackpoll Warblers look completely different in fall from their black-and-white breeding plumage. A hatch-year male caught on 9 October, however, had quite a few black feathers on its crown and throat, hinting at the stripes that he will grow in his pre-alternate moult in South America, leaving no-one doubting the aptness of its scientific name of Dendroica striata.

After this glorious week, with the capture of the Yellow Palm Warbler, the set of the likely fall warblers was almost complete for 2005, but we were still ‘pining’ for Dendroica pinus! Then, on Sunday 9 October, a Pine Warbler made it into one of the nets, three years to the day after the last one banded at Powdermill, on 9 October 2002. They are not such a scarce bird, of course, but the habitat on the reserve is not particularly suitable and they seldom are caught here, making Pine Warbler a ‘good get’ in the local jargon. The photos below rather nicely show the unstreaked back that helps to distinguish this species from basic-plumaged Blackpoll and Bay-breasted Warblers with which they sometimes are confused.

The conditions at Powdermill Nature Reserve are obviously to the liking of some birds, which stay to fatten up for their forthcoming long migratory journey. This is nicely illustrated by two adult male Connecticut Warblers recaptured during the week that showed substantial weight gain. One had been caught five times in 11 days, going from 13.6g to 17.9g, and the other six times in 19 days, rising also from 13.6g to a 'supersized' 18.9g. Just after this period, on 11 October (just in time for this writing), he was caught again, tipping the scales at 19.0g! But, 24 days after his first capture, why has he not gone?

Indeed, a remarkable feature of the day's catch on Sunday 9 October was the excellent energetic condition of the nearly all of the birds handled. Out of our total of 382 banded and recaptured birds, more than half (210) were recorded as having the maximum fat deposit of "3" on our scale of 0-3; only 57 birds were scored with "0" fat. This suggests that the majority of birds caught had not arrived at Powdermill after a long night's migration, but rather had been in the area feeding and fattening for at least a few days. It is difficult to know for sure, because we did not band at all on Friday due to rain, and had a very late start on Saturday for the same reason.

Many of these birds made us wish that we had a greater range of fat scores available. Bob Leberman settled on a 0-3 scale in 1961, when fat scoring of any kind was a rarity, and this system has stood the test of time at Powdermill. The normal European system is to use a nine-point scale, from 0 to 8, and adoption of this scheme for North America was recommended recently (Erica H. Dunn, Recommendations for Fat Scoring, North American Bird Bander 28: 58-63 (2003)). After much debate, this scheme was adopted ten years ago for the European-African Songbird Migration Network funded by the European Science Foundation (ESF) and chaired by Professor Franz Bairlein. The following chart is taken from the Manual of Field Methods for that project, with the gray stippled areas representing deposits of fat, on a schematic bird viewed in profile and looking straight down on its underside.

A Blackpoll Warbler banded on 9 October illustrates the point:

In this ungainly and unusual photo, the bird’s head is to the top, and its abdominal feathers have been wetted to make them temporarily stay parted; the yellow areas are the subcutaneous fat and the red is the remaining part of the abdomen not (yet) covered with fat. This bird, a hatch-year male weighing 19.0g, was carrying about 8g of fat and would be scored close to a 7 on the ‘ESF’ scale. There has only been one heavier Blackpoll Warbler at Powdermill out of the 320 handled in the last ten years.

Crowning a great week, all agreed that Sunday 9 October 2005 was one of the very best banding days ever in the 45-year history of the Powdermill banding program! This verdict was shared by Bob Leberman and Bob Mulvihill, and they should know, because one of the ‘Powdermill Bobs’ has been here for every big day – and many not-so-big – in that time. Not only was the overall number of birds very high (our 16th highest daily total ever), but the species diversity was exceptional for October (15 species of wood warbler alone!): 43 species newly banded, and a further six species amongst the recaptures, making 49 species handled in the day. Among these was the late HY female Prairie Warbler pictured above. Only four PRAWs have been banded on a later October date than this, the latest being 19 October 1978.

Finally on Sunday evening, just when we were winding down and feeling that things could not be any better, we received the excellent news that Annie Lindsay had passed the North American Banding Council certification course held this weekend at Braddock Bay Bird Observatory. Annie has been a volunteer, then intern, at Powdermill for several years, and is now the third Powdermill staff member to have achieved NABC certification in the last couple of years, helping to maintain the high standards of banding here.

What a week! And what a great banding site! I feel privileged to be playing a small part in the work of the Powdermill Avian Research Center. I especially thank Bob and Adrienne for the opportunity to ‘guest-author’ their website before I return home to my own efforts on http://www.merseysiderg.org.uk/.

< HOME >
Return to Past Pictorial Highlights

Last Updated on 10/11/05
By David Norman