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Bohemian selectively feeding on the stamens of Silver Maple Winnie Poon

Introduction cast 2007-2008 (Pittaway 2007). At the In the winter 2007-2008, Ontario expe - same time, a massive crop failure of the rienced its largest winter finch irruption native Mountain Ash ( Sorbus decora ), in the last ten years. Many boreal finches also occurred across much of northern irrupted well south of their normal Ontario. Mountain Ash berries normally ranges, following the largest coniferous provide an important winter food for and deciduous tree seed crop failure in a Bohemian Waxwings ( Bombycilla garru - decade across the boreal forests in much lus ) across boreal regions of Canada, but of Ontario and western Quebec. This the 2007 crop failure evidently precipi - event unfolded exactly as forecasted by tated another irruption of this species Ron Pittaway in his Winter Finch Fore- across eastern North America.

Figure 1. Location where the Bohemian Waxwings were seen feeding; the flowering Silver Maple is nearest the picnic table. Alden Road, Markham, York , 8 April 2008. Photo: Winnie Poon

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This irruption turned out to be the Markham, York Regional Municipality. largest ever recorded in the Greater The waxwings were reported to be feed - Toronto Area (GTA) and adjacent south - ing on “fallen shoots”, and also “newly ern Ontario (Poon 2008). It lasted from opened shoots” on the trees. Intrigued by approximately mid-October 2007 to the this report and being curious as to what third week of April 2008. It was very the “shoots” would look like, Roy Smith extensive in terms of numbers, geo - and I arrived on site on 5 April for a clos - graphic area covered and duration. With - er look. in the GTA, it surpassed the previous There were already six other birders record of 1999-2000, and even the influx enjoying the bird activities when we of 1958-1959, which Gunn (1959) des - arrived at 1420 h. The location was the cribed as “the largest of the century”. front lawn of a small industrial building But the most notable feature of the on the southeast corner (Mactec Canada 2007-2008 irruption was the returning – 555 Alden Road) (Figure 1). Close to wave of waxwings in spring, that resulted the front door of the building was a 7 – 8 in an unprecedented number of April m tall Silver Maple ( Acer saccharinum ) in records for the GTA, especially within full blossom. There were two other small - the City of Toronto. The number of er maple trees about 10m north, but both records in the database of the Toronto had wilting blossoms. Around the north - Ornithological Club reached 48, whereas east corner, at the back of the side yard, only eight previous years had April was a row of four very thin Highbush records, and then only 1 to 3 each. It is Cranberry ( Viburnum opulus ) bushes acknowledged that the database may be that were devoid of berries, except for incomplete for some earlier years. It was some fallen ones on the lawn beneath. during this returning wave that the Most of the winter snow had melted, apparently rarely seen feeding behaviour leaving about 5% of patchy snow cover of Bohemian Waxwings eating the sta - on the lawns, and exposing the fallen mens of a Silver Maple tree ( Acer sacchar - fruits as noted. Lining the sides of the inum ) was recorded. lawn were 6 small, bare ash trees. Also, across Alden Road were seven other simi - Circumstances lar maples in bloom. On 3 April 2008, Siegmar Bodach posted We counted at least 38 Bohemian to ONTBIRDS (the listserve of the Waxwings, but no Cedar Waxwings. The Ontario Field Ornithologists) that a majority were feeding actively on the one flock of about 35 Bohemian Waxwings Silver Maple at the front door, but not on and 9 Cedar Waxwings ( Bombycilla the other maples in the area. Sometimes a cedrorum ) had been seen near the inter - group would perch on one of the smaller section of Alden Road and Hood Road in bare ash trees, perceivably resting after a

ONTARIO DECEMBER 2008 167 good meal, while several times these that the birds might be after the pollen birds flew down to a manhole cover near - instead. I investigated further using my by and drank from melt water that had telescope, concentrating on one feeding collected there (Figure 2). At times, a few . The bird appeared to be pluck - birds would split off and fly to the High - ing off and eating only the stamens, leav - bush Cranberry bushes, dropping to the ing the small red petals intact on the ground to eat the remaining fallen fruits. flowers that it was feeding on. It required All the birders were about 8-10m much concentration and time to see the from the maple tree and waxwings which bird swiftly plucking off the stamens, were pecking incessantly at what app- even with the help of a scope at close dis - eared to be clusters of tiny reddish buds tance. At this point, I digiscoped many on the branches. Using binoculars, I photographs of a feeding bird, including could see that the birds were not pluck - two series of continuous burst mode ing off and consuming the buds, but photos. Afterwards, by examining one of instead were just dipping their bills into these series frame by frame, I was able to the buds. I examined closely a clump of confirm that the bird was eating only the these buds in my hand, and was surprised stamens (filaments and anthers), while to find that from each tiny bud (flower) the outer parts of the flowers remained were many long and thin filaments (sta - untouched from the first frame to the last mens) with richly laden yellow pollen (Figure 4). These photos provide materi - pods at the tips (anthers) (Figure 3). al evidence of the Each clump was a mass of newly consuming stamens from a Silver Maple opened maple flowers and I suspected tree in spring.

Figure 2. Nine Bohemian Waxwings drinking from meltwater on manhole cover at Markham, York , 5 April 2008. Photo: Winnie Poon

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Discussion In winter, Bohemian Waxwings are pri - marily berry and fruit-eaters, utilizing a wide variety of fruits for their winter sur - vival. In Ontario, some of these fruits are Mountain Ash, crab-apple ( sp .), buckthorn ( Rhamnus sp .) , ( Juni - perus sp .), bittersweet ( Celastrus sp. ), dogwood ( sp. ), and Highbush Cranberry. When available, Bohemian Waxwings may also feed on protein-rich (Witmer 2002) and tree buds, including American Elm ( Ulmus ameri - cana ) and ash ( Fraxinus sp.) (Pittaway 1990), as well as maple ( Acer sp.) (Elder 2002).

Figure 4. Bohemian Waxwing feeding on the maple tree, note that the bird has three anthers in its bill and that most of the stamens have been nipped off the flowers directly in front of it. Markham, York , 5 April 2008. Photo: Winnie Poon

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Figure 3. Clusters of blooming Silver Maple flower. Each flower had at least 14 -15 stamens with extremely long filaments. The anthers were large and reddish-yellow in color when fresh. Markham, York, 8 April 2008. Photo: Winnie Poon

During spring, the waxwings may also may have been observed before. Bent feed on sap drips from maple and birch (1950) quoted Swarth (1922) that (Betula sp.) trees (Bent 1950). However, Bohemian Waxwings “...were seen feed - for North Am er ica, there seems to be no ing on insects and also on berries and published record of Bohemian Wax - other vegetable matter”. Although this wings selectively consuming flower sta - quote may be suggestive, there is no spe - mens, despite the possibility that this cific mention of this species consuming

VOLUME 26 NUMBER 3 170 flower parts in Bent's account. Witmer apple, pear, cherry, oak, maple and ash, (2002) also quoted from Bent (1950) and it doubtless eats stamens of many that the Bohemian Waxwing “often feeds other varieties”. But for Bohemian Wax- on flowers of trees and shrubs in spring”. wing, Barrows only noted that “...this It is possible that Witmer drew the above bird feeds mainly on the same berries, quote from Bent’s account of the Cedar seeds and fruits as the Cedar-bird...”. Waxwing, since it is commonly accepted More recent studies on the Cedar that the two North American species of Waxwing found that flowers, including waxwings share similar dietary and feed - stamens, comprised only 4% of the ing habits. Undoubtedly, Bohemian annual diet, but in May, when fruits are Waxwings have often been seen eating scarce, they could amount to 44% of the the same foods as Cedar Waxwings, and diet (Witmer 1996). Flower petals may it seems logical to assume that the results provide sugars, while pollen on stamens of certain studies of Cedar Waxwings can provides protein. Consumption of plant be extrapolated to Bohemian Waxwings species that do not have showy petals or as well. nectar rewards ( Acer , oaks — Quercus , Bent’s account of the and poplars — Populus ) indicated that contains a number of statements with the waxwings were partly motivated to regard to flower consumption; including consume pollen. Witmer also observed the following: that Cedar Waxwings ate the staminate I “The only other vegetable food of cat kins of Eastern Cottonwoods ( Populus importance in the diet of the Cedar- deltoides ) in combination with Highbush bird is flowers” Cranberry in spring, this observation I “At New Orleans...about Feb.1, when subsequently led to his conclusion that it arrives to feed on the fruit of hack - this diet-mixing behaviour was a strate - berry and Japan privet, and the flow - gic choice for the waxwings at that time ers of the elm. It later feeds on the of year. blossoms of the pecan...” The inter-relationships between the I There are several records of cedarbirds fruiting ecology of Highbush Cranberry, eating the petals of apple blossoms. and the food requirements of Cedar As for Cedar Waxwing specifically Waxwings, were carefully unravelled by consuming flower stamens, one early Witmer (1994 , 1996, 1998, 2001). report (Barrows 1912), states that “Dur - Starting with field observations, he noted ing spring and early summer the Cedar- that Highbush Cranberries tended to be bird appears to be very fond of blossoms, ignored by most bird species during the and especially of the stamens, of many late fall and early winter, and only eaten trees, particularly fruit trees. We have by Cedar Waxwings in late winter and seen it frequently eating the stamens of spring, when alternative fruit resources

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Figure 5. Dessicated V. opulus fruits can persist until late spring. Toronto , 22 May 2004. Photo: Winnie Poon would be at minimum levels. Other presented samples of early winter fruits species virtually ignored it. One might (preserved by freezing), and late winter assume that these Highbush Cranberry ones to caged Cedar Waxwings, he found fruits are generally unpalatable to birds, that his experimental birds preferred the or perhaps contain insufficient energy or early winte r fruit over the aged fruit . protein to be ‘worth eating’, but Witmer By the natural process of ageing and found that the aged fruit in late winter dessication, late winter or aged fruits did contain enough simple sugars to (Figure 5) contain higher concentrations meet the birds’ energy needs, albeit defi - of secondary compounds that help pre - cient in nitrogen content. When Witmer serve them against microbial and fungal

VOLUME 26 NUMBER 3 172 attack. Among the four classes of second - series of experiments using caged Cedar ary compounds: alkaloids, cyanogenic Waxwings tested with various combina - glucosides, terpenes, and phenolics, the tions of aged Highbush Cranberry fruits latter two especially will produce strong and the staminate catkins of P. deltoides . organic acids if metabolized. Thus, the The results showed that the birds pre - physiological challenge in consuming ferred and sought out a mixed diet of Highbush Cranberries is that they con - both types. He went on to establish tain a phenolic compound (chlorogenic experimentally that Cedar Waxwings fed acid) that renders the fruits extremely on catkins alone did not obtain sufficient acidic (ph 2.8 – 3.0). In addition, the energy to maintain their body mass. Sim - osmotic load of simple sugars in dessicat - ilarly, birds fed on aged V. opulus fruits ed persistent fruits likely creates a need alone did not thrive and started to lose for supplemental water as well (Studier et body mass; in fact, results suggested that al. 1988), and waxwings often need to secondary compounds in the fruit exac - drink water or eat snow to meet the erbated nitrogen losses in the birds. Evi - demand for water. dently, waxwings need supplementary Witmer observed that Cedar Wax - nitrogen (from pollen) in order to cope wings often ate the staminate catkins in with the aged fruit. Furthermore, Cedar early spring. But during most of the year, Waxwings seem to be more efficient at they are one of the most obligate frugi - digesting the protein contained in P. del - vores found in North America, and can toides pollen, with a relative value of 89% easily survive for long periods on sugary quoted, versus a value of <50% for pro - fruits alone. So why would they need tein digestion obtained in most studies of supplemental protein at this time? Wit - other birds (Witmer 2001). It is beyond mer guessed, correctly as it turned out, the scope of this paper to discuss the sci - that the waxwings required the protein entific evidence in great detail here, but content from the pollen in these catkins readers can refer to Witmer (1994, 1996, to balance their bodily ph during the 1998, 2001, 2002) and other sources early spring period, when food is in quoted therein. short supply. To counteract the acidity in Witmer concluded that “...The asso - metabolizing Highbush Cranberry ciation of waxwings and V. opulus appears fruits, nitrogen (amino acids) is required to be a result of the distinctive dietary in the physiological mechanism for acid habits of waxwings and the extreme buffering, producing bicarbonate and persistence of these fruits”. He went on ammonium in the process. Eventually, to note that “The nutritional key that bicarbonate is respired off as carbon diox - enables waxwings to feed on these ener - ide, and ammonium is excreted in the gy-rich, but unpalatable, fruits is the urine. He supported this hypothesis by a sudden appearance of a complimentary

ONTARIO BIRDS DECEMBER 2008 173 protein source with the springtime useful tool in birding made it easier to emergence of staminate flowers.” (Wit - obtain good photographs. mer 2001). There must be a relatively narrow As a result, the fruits of Highbush window of opportunity in April and Cranberry survive, mostly uneaten, until early May in northeast North America, early spring, when they become available when newly opening flowers of various to wandering flocks of wax wings, and tree species provide the supplemental the plant achieves potential long-dis - protein that wandering flocks of tance dispersal of its seeds. waxwings require in order to process the persistent dessicated, but well preserved Conclusion and chemically laden fruits of V. opulus . In view of the above information, it Presumably, other frugivores such as became clear that the feeding behaviour ( Turdus migratorius ) are of the Bohemian Waxwings observed on unable to handle this and so seldom eat 5 April 2008 was exactly analogous to these fruits. Witmer may not have had the mutualistic relationship between an opportunity to study Bohemian Highbush Cranberry ( V. opulus ) and Waxwings under the same circum - Cedar Waxwings proposed by Witmer. stances, but the observation recorded in It seems that Bohemian Waxwings are Markham on 5 April 2008 suggests that almost certainly subjected to the same given the right conditions, their feeding physiological stresses and requirements behaviour may be exactly analogous. as Cedar Waxwings when consuming Cedar Waxwings are great wanderers, V. opulus fruits in spring. The rare and Bohemian Waxwings even more so oppor tunity to observe this feeding during their irregular irruptions. Hence, behaviour of Bohemian Waxwing was from the plant’s perspective, to be des - probably ena bled by four factors. Firstly, cended upon by a flock of Bohemian the 2007-2008 irruption lasted longer Waxwings would be the equivalent of than in most previous years, allowing the hitting the seed dispersal jackpot! waxwings to linger well into April. Sec - ondly, because they stayed later than Acknowledgements ‘normal’, the presence of some birds Firstly, my sincere thanks to all the observers coincided with the flowering of Silver who reported their Bohemian Waxwing sight - Maple trees. Thirdly, site conditions pro - ings on ONTBIRDS and elsewhere, which vided three key components — available raised awareness and a great deal of interest in the last irruption. Thanks to Roy Smith for his Highbush Cranberries, freshly emerged valuable inputs and edits of earlier drafts. My stamens, and water from the melting special appreciation goes to the editors of snow, in close proximity. Lastly, the Ontario Birds for a final review of this article. recent development of digiscoping as a

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Literature Cited Witmer, M.C. 1994. Contrasting digestive strategies of fruit-eating birds. Ph.D. disserta - Barrows, W.B. 1912. Michigan Bird Life. tion, Cornell University, Ithaca, New York. Michigan Agricultural College Special Bulletin. East Lansing, Michigan. Witmer, M.C. 1996. Annual diet of Cedar Waxwing based on U.S. Biological Survey Bent, A.C. 1950. Bohemian Waxwing, records (1885-1950) compared to diet of pp.62-79 and Cedar Waxwing, pp. 79-102. American Robin: contrasts in dietary patterns Life Histories of North American , and natural history. Auk 113:414-430. Shrikes, Vireos, and their Allies. Dover Publications, Inc., New York Witmer, M.C. 1998. Ecological and evolu - tionary implications of energy and protein Elder, D.H. 2002. Feeding Behaviour of requirements of avian frugivores eating sugary Bohemian Waxwings. Ontario Birds 20:19- diets. Physiological and Biochemical Zoology 20. 71:599-610. Gunn, W.W.H. 1959. Ontario-western Witmer, M.C. 2001. Nutritional interactions New York Region. Audubon Field Notes and fruit removal: Cedar Waxwing consump - 13:289-292. tion of Viburnum opulus fruits in spring. Pittaway, R.J. 1990. Bohemian Waxwings Ecology 82:3120-3130. eating tree buds. Ontario Birds 8:75-76. Witmer, M. C. 2002. Bohemian Waxwing Pittaway, R. J. 2007. Online. Winter Finch (Bombycilla garrulus ). In The Birds of North Forecast 2007-2008. Accessed 15 September America, No. 714 (A. Poole and F. Gill, Eds.). 2008. < http://www.ofo.ca/reportsandarti - The Birds of North America, Inc., cles/winterfinches.php>. Philadelphia, Pennsylvania. Poon, W. 2008. The Bohemian Waxwing Irruption 2007-2008. Toronto Birds 2:72-78. Winnie Poon , 1002 – 20 Harding Boulevard Studier, E.H., E.J. Szuch, T.M. Tompkins , West, Richmond Hill, Ontario L4C 9S4 and V.W. Cope . 1988. Nutritional budgets in free flying birds: Cedar Waxwings ( Bombycilla cedrorum ) feeding on Washington hawthorn fruit ( phaenopyrum ). Comparative Biochemistry and Physiology 89A:471-474. Swarth, H.S. 1922. Birds and mammals of the Stikine River region of northern British Columbia and southeastern Alaska. Universi - ty of California Publications in Zoology 24:125-314.

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