• We ended the summer season this week (July 28 - August 1st) with a total of 1500 birds banded, making summer 2004 a record setting season for Powdermill Nature Reserve (previous high was 1327 in 1993).  This accomplishment was greatly influenced by July's total of 1101 birds, 76 birds more than the previous all time July record high of 1025 birds.  American Redstarts continued to dominate our catch, however, Hooded Warbler pushed out Gray Catbird for the second place spot.  Mike Comley, Randi Gerrish, Annie Lindsay, Cokie Lindsay, Trish Miller, and Felicity Newell all helped with banding this week.

• We banded a hatching year (HY) male Canada Warbler (left) on the first day of the week.  Unlike the CAWA banded last week whose sex we did not feel confident in determining (i.e., its plumage was female-like while its wing length suggested male), the sex of this week's bird was unambiguous (i.e., its plumage traits--the blackish, rather than grayish necklace, and wing length of 63.5 mm, both were in agreement with its being a male).

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• As we have pointed out many times before, in species like the CAWA in which immature males do not acquire a plumage in their first fall that is anywhere near as bright as an adult male, the two age-sex classes most easily confused in fall on the appearance of overall plumage alone are HY males and AHY females.  AHY males in these species frequently are just about as bright in their fall plumage as in spring and HY females are at the very drab end of the plumage gradient for the species (it is the immature females which comprise the so-called "confusing fall warblers").   The importance of getting the age right for correctly assigning sex also applies in the case of Kentucky Warbler, as discussed below.

• On Wednesday, July 28th, we banded the HY male Kentucky Warbler pictured below.  As with the CAWA pictured above, this young male KEWA closely resembles an adult female in overall plumage (i.e., brighter than an immature female but not as bright as an adult male), so correctly sexing the bird depended on correctly ageing it.  What distinguished this as an HY KEWA was the very fresh plumage and presence of a distinct molt limit in the alula (the small proximal feather of the three-feathered alula, what we call the alula covert, is molted during the incomplete first prebasic molt, while the two larger alula feathers are retained from the juvenal plumage).

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An adult KEWA likely would not have completed its prebasic molt of wing and tail feathers by this point in the season and, therefore, would have worn wing feathers, or it would actively be molting flight feathers, feathers that are not replaced by HY birds in their first fall.  If an adult had, in fact, completed its molt by this time, its plumage would be fresh, however, because it had replaced all the feathers of its wing, it would not have a molt limit.  As we move further into the fall season, i.e., as increasing numbers of adults finish their complete prebasic molt, we will increasingly use skulling (i.e., careful examination of the degree of pneumatization of the skull, as seen by parting the feathers on the crown of the head and looking through the thin transparent skin overlying the skull) to corroborate our impressions of birds' ages based on apparent molt limits or lack thereof.

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• The story behind our recent recapture of the motley looking Louisiana Watertrhush pictured below is a long story that simply can't be made too short without losing interesting information!  So, here goes...

• For being the earliest of all eastern warbler fall migrants (records of migrants through Florida as early as June 9th), the LOWA pictured above (and below) certainly is one of the latest molting waterthrushes we have ever seen at Powdermill.   In fact, by the end of July, LOWAs ordinarily are all but gone from Powdermill, having already completed their "fall" molt.

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Caught in our nets on Wednesday, July 28, this previously banded (in April 2003) tailess adult (ASY) male Louisiana Waterthrush had yet to drop its outermost primary or its five middle secondaries (see photo below).  With a total molt score of just 40 (out of a possible 90) on its right wing, it was not yet halfway through its prebasic molt. --The total molt score is the sum of the individual molt scores for all 18 flight feathers, with the old, unmolted feathers being scored "0" and molting primaries and secondaries scored "1" (just dropped or in pin) to "5" (freshly molted and fully grown)--
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In the very well-studied population of LOWAs around Powdermill, adults typically have completed their prebasic molt (i.e., have achieved a total molt score of 90) by the end of July.  Given the species' typical molt rate of about 2.2 molt score points per day, the bird pictured below would not be expected to complete its molt until about August 20th, or three weeks later than normal.  Based on our studies, such late molting birds almost always have experienced delayed onset of molt due to late renesting or (very, very rarely in LOWAs) to double brooding.  And, even with delayed molt onset, such late nesting birds (unlike earlier nesting birds) usually end up overlapping their molt to some degree with parental care associated with their late nesting attempts.  We have observed later nesting LOWAs initiating their molt while still caring for older nestlings or recently fledged young.
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The LOWA pictured above and below was caught (not yet having even begun its molt) in the same net with a recently fledged, stub-tailed juvenal back on July 3rd.  Median fledging date for LOWAs at Powdermill is June 4, so this bird either had had one or more earlier failed nesting attempts (we have observed LOWAs make as many as four attempts in the same season), or else is one of the very few (out of several hundred nesting pairs studied in the last nine years) to have had two successful broods in the same season.   In fact, its late hatched offspring appears twice on the pictorial highlights page from the first half of July:  first when it was originally caught on July 3 and shown in comparison with a juvenal Ovenbird; second, when it was caught a week later (on July 11th), still in full juvenal plumage, in side-by-side comparison with a much earlier hatched HY LOWA that already had nearly completed its prebasic molt (as most young LOWAs have at Powdermill by the beginning of July).
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We'll get a little ahead of ourselves and tell you that this same adult was recaptured again on August 4, when its molt had advanced by another 20 molt score points (giving a calculated molt rate somewhat higher than the average 2.2 points/day).  At this rate, it still will not have completed its molt until just after the middle of August, by which date some adult LOWAs (and their offspring) from our Powdermill population may already have arrived on their Central American wintering grounds!  Clearly, the inevitable delays in molt and migration associated with late nesting in the LOWA are a significant cost that largely negates any selective advantage of producing a second brood of young.  This, in turn, goes a long way toward explaining the evident rarity of double brooding as a life history strategy in this species.  Thinking back on how much more we know from having banded (and recaptured) this one adult LOWA and its one fledgling, the immense value of banding for the scientific study of birds is immediately apparent!

 

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• Friday, July 30, our highlight for the day wasn't a bird but a wonderful group of teachers from Mexico who visited the station for a banding demo.  In a trip funded by PPG Industries and Bayer Corporation, and arranged as part of a "Wings of Wonder" project of the Wildlife Habitat Council, eight teachers and administrators from schools in San Juan del Rio spent two days at Powdermill learning about ways that we study the birds whose annual migrations link Pennsylvania and their region of central Mexico.

 

 
 
 

The photo below shows the visiting group flanked by Powdermill banders Bob Mulvihill (back left), Bob Leberman (back right), and Adrienne Leppold (holding a Northern Parula at bottom right), and Powdermill's Director, Dr. David Smith (far right).  In the center of the group, in the black t-shirt, is Marcia Maslonek, Director of the Tri-State office of the Wildlife Habitat Council, who arranged the trip as part of that officie's Three Rivers Habitat Partnership.

• Below, nine year old Matthew Medrano, carefully holds (then releases) a just banded Red-eyed Vireo.

 

 

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• Finally, on the last two days of the week, we banded our final three new species for the summer season, an HY female Black-throated Blue Warbler (top photo) and HY female Golden-winged and Blue-winged warblers (together in bottom photo).

• The week of July 20th - July 25th continued to be busy with two out of five days netting more than 100 birds. 43 Gray Catbirds came in second to the 96 American Redstarts banded this week.  As mentioned last week, amazingly, the bulk of these birds are not "true" migrants but simply hatching (HY)  year birds from local areas that have begun dispersing out of their natal territories while molting and preparing for migration.  The main migration passage of redstarts through Powdermill really doesn't start for another month!

 

 
 
 
 
 

As the season progresses and we get busier and busier, we become increasingly grateful for our string of volunteers and interns who help each week.  Mike Comley, Randi Gerrish, Jim Gruber, Annie Lindsay, Trish Miller, Ian Moffatt, Felicity Newell, and Paul Sweet all helped with banding this week, THANK YOU!

• On the first new day of the week we caught the first of three new species banded for the summer season, this adult (ASY) female Worm-eating Warbler.  This species' long term summer average at Powdermill is less than one, so it was a welcome sight in our nets (a second WEWA, a HY of unknown sex, was banded on the 21st).

• In the summer, we expect the feathers of adult birds (both SY's and ASY's) to be somewhat to very worn--especially on the wing--and HY birds to have very fresh, unworn feathers.  Beginning about this time of the summer season, however, adults of some species (here at Powdermill, including American Redstarts and Yellow Warblers) begin showing up in our nets having completed or nearly completed their prebasic (fall) molt and, therefore, also have a fresh, unworn wing plumage.  At a quick glance, the first freshly molted adults caught might be confused as HY birds, given that degree of wing wear, or the presence of actively molting flight feathers, has served to separate the two age classes readily up to this point in time.

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Notwithstanding the above-stated general principle, the wing plumage of the ASY female WEWA banded this week was neither worn nor freshly molted.  Still with an old B.P., and not yet having even begun her prebasic molt, this female's wing feathers, which molted in almost a year ago, were astonishingly unworn!  Only a few outer lesser and median coverts show obvious wear.

• Last week we posted a comparison photo of male and female HY Black-and-white Warblers, and we mentioned that neither HY nor AHY males have black throats in the fall.  The photos below illustrate this.  The bird on the left is a second year (SY) male banded this spring in full breeding/alternate plumage.  The bird on the right is a second year (SY) male banded this week (aged by the molt limit still visible among its as yet unmolted alular feathers).  It was actively molting into winter/basic plumage, already having replaced the black throat patch.  The molting SY male on the right differs in plumage from the HY male pictured last week by the presence of a dark cheek patch (still molting in).

• All but seven (84%) of our 43 catbirds banded this week were HY birds.  So, when we had the odd round where we caught an adult and juvenile together, we took the opportunity to photograph them together.  Recently, we have been pointing out the difference in structure of juvenal vs. adult feathers,  and this photo shows that even when the plumage color and pattern of adults and young is not very different, the loose structure of juvenal feathers (bird on the right) is distinctive.   Also, the classic "baby" gape in the HY bird is still very evident.  This yellow fleshy part of the bill on the corners of the mouth serves as a directive mark for the adults upon returning with food to the nest or, as in the case below, a fledgling.  This fleshy gape will soon disappear as the bird ages and its "soft parts" fully develop.

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• Throughout the last week we have been hearing a lot of Eastern Screech Owls calling near the banding headquarters, so we were inspired to try to call them into the nets a few nights this week.  Our first night was a success with the capture of this squinty-eyed HY bird netted on the last net round before we closed our nets for the night.

• Our second night of owl banding wasn't quite as successful as the first, but on closing the nets after the last round, we found a very different (but not totally unexpected) nocturnal creature--a hoary bat (Lasiurus cinereus)!  The largest bat in eastern North America, this species is easily identified not only by its large size, but also by its distinctive "hoary" appearance (chocolate brown fur frosted with white) above and yellow-furred underwings.  Hoary bats typically are very aggressive in the hand and this one was no exception!  In general, captures of bats in mist nets at Powdermill, even when the nets are being operated at dusk and after dark for owls, are very infrequent, and this was only the second hoary bat we've caught in more than twenty years.

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• To conclude, a couple final warbler highlights from Saturday, July 24th:  an HY male Cerulean Warbler (top photo) and an HY Northern Waterthrush (bottom photo).

• The NOWA was not a new species for our summer (June-July) banding season.  Our two previous "summer" NOWAs were banded on June 1st and June 6th.  While the breeding range of the species extends as far south as the Appalachian Mountains of West Virginia (including northern Pennsylvania and the Allegheny Mountains to the east of Powdermill), none of our "summer" NOWAs are breeding birds.   June banded NOWAs are among our very last spring migrants, and the HY bird banded this week (with a maximum fat load) was among the very first unequivocal fall migrants.  So, the period of time separating the spring and fall migration periods for songbirds at Powdermill is surprisingly brief (about six weeks).

• Click here for the gallery of Powdermill Nature Reserves "baby" pictures from fledgling birds banded over the past two months.  Note:  You will have to use your browser back button to return to this page from the links above.

Last Updated on 8/07/04
By Robert S. Mulvihill