Any day now the skies over Eastern Ontario will begin to ring with the calls of Red-shouldered Hawks (Buteo lineaus). This vocal hawk is one of the most commonly encountered raptors on the Frontenac Arch. It’s also one of the few forest raptors that have been subject to long term monitoring in Eastern Ontario. Beginning in 1991 the Red-shouldered Hawk and Spring Woodpecker Survey has been conducted each year along Opinicon Road in an effort to keep track of Red-shouldered Hawk numbers. In this post I summarize the results of 20 years of counting Red-shouldered Hawks along Opinicon Road. The counts were completed by Ron Weir and others. Thanks to Ron for providing me with the survey data.
The results of the Red-shouldered Hawk surveys show that there has been a significant increase in Red-shouldered Hawk numbers since 1991 (P=0.0013). The lowest count was 5 birds in 1992. The highest count was 27 birds in 2003. The mean count is 17.05 birds. Red-shouldered Hawk numbers across their Ontario range appear to be steady or increasing and the data from Opinicon Road matches this trend.
QUBS is situated in what is currently the heart Red-shouldered Hawk abundance in the province (Cadman et al 2007). The largely intact forests that cover our part of the Frontenac Arch provide habitat for these sylvan raptors and are likely the reason for the high numbers recorded here. Red-shouldered Hawks may have been far more abundant than they are today all across Ontario prior to the conversion of forests to farmlands (Weir 2008). The species continued to decline in the mid 1900’s. In 1983 the Red-shouldered Hawk was designated a species of concern in Canada, due to the large declines in populations associated with forest clearing. In 2006 it was reclassified as not at risk. Today the most commonly observed hawk in the region is the Red-tailed Hawk (B. jamaicensis). It prefers large tracts of farmland or other open terrain. It has probably replaced the Red-shouldered Hawk throughout much of southern Ontario as a direct result of habitat alteration. However, at QUBS Red-shouldered Hawks remain more numerous than Red-tailed Hawks on most of our tracts.
Cadman, M.D., Sutherland, D.A., Beck, G.G., Lepage, D. and Couturier, A.R. (editors). 2007. Atlas of the Breeding Birds of Ontario, 2001-2005. Bird Studies Canada, Environment Canada, Ontario Field Ornithologists, Ontario Ministry of Natural Resources and Ontario Nature.
Weir, R.D. 2008. Birds of the Kingston Region 2nd edition, Quarry Press, Kingston.
For August and September, 2010, I helped a student, Amy McMullin, conduct experiments in the ‘field’ at Round Lake. We measured the physical parameters (i.e. temperature, oxygen, light), sampled the zooplankton and ran experiments with live critters (Daphnia) in bottles at different depths. Our study species was D. pulicaria (a water flea, left figure), a key component in many lake food webs where they consume tiny plants, the phytoplankton, and in turn, Daphnia are food for insect larvae (such as the Phantom midge) and for larval or juvenile fish. The top predator at Round Lake seemed to be a pair of loons residing at the lake over the summer and their single offspring (young with their mother, below right).
Round Lake is appropriately named for its circular shape. The steep sides plunge down to a maximum depth of 30 meters. The more gradual shore on the SE side is where we launch the boat. One of the interesting features of this lake is the low oxygen in the bottom waters (i.e. 0.26 -0.10 mg/L from 15 m & below, Aug. 31/10). As we were setting out and retrieving the Daphnia from jars in the water at 15 and 20 meters, I kept finding lovely dark pinkish-red clusters of cells in the water from the 20 m depth (Amy worked on the 15 m samples). At first I wondered why there were red algae at a depth of 20 meters since we had measured the amount of light and it was extremely low! I realized that it was not an algae after seeing an article on ‘Bahamas Blue Holes’ in National Geographic (August, 2010). The articles’ description of diving through a zone of pink stained water (a layer of purple sulfur bacteria), made a strong impression. As it turned out, the purple sulfur bacteria are inhabitants of freshwater environments as well as saltwater. After examining some of the pinkish-red stuff under the microscope, the cells were easily identified as the purple sulfur bacteria, Amoebobacter (Pfennig and Trüper, 1989). Even though the individual round cells are only 2-3 microns across, the colony is held together by wispy strands of mucus and so the bacteria are very easy to see with your eye.
What do the purple sulfur bacteria need to persist? Like plants, they photosynthesize, but they use bacteriochlorophyll and carotenoids to capture light energy at wavelengths quite different from the ones used by algae (Pfennig and Trüper, 1989). In addition, the purple sulfurs can photosynthesize at light levels 500 times lower than that available in the water’s surface layers on a sunny summer’s day. They are not as efficient at photosynthesis as the phytoplankton but they also grow in darkness and can adjust their buoyancy depending on their needs (Overmann and Pfennig, 1992). In summary, the purple sulfur bacteria need sulfide compounds, have species specific ranges in temperature, need low oxygen or no oxygen for growth, and, have a wide range of salinity tolerances. As mentioned, purple sulfurs grow in high salinity as in the Bahamas, salty lakes (Mahoney Lake, B.C.), or, in fresher water such as Round Lake. Not surprisingly, the purple sulfur bacteria are thought to have arisen a long time ago (1.6 billion years before present; see Brocks and Schaeffer, 2008) when there was not a lot of oxygen in the oceans and the cyanobacteria were just getting started. Daphnia, on the other hand, have been around since “at least the Permian” (299 – 251 million years ago; Taylor et al., 1999).
In Round Lake Daphnia pulicaria are found throughout the water column. Some individuals are found in the low oxygen water, why are they there at all? We noticed that some live specimens have an obvious red coloration that has been noted by other researchers and studied in Daphnia. Like their predator found in Round Lake, the phantom midge Chaoborus flavicans, Daphnia produces hemoglobin in their bodies when they have been under low oxygen stress. It is their interesting adaptative plasticity and their suitability for lab experiments, which make Daphnia a good organism for studying energy budgets in Bill Nelson’s lab at Queen’s.
There are many unanswered questions about the plankton community and the physical features of Round Lake. I had hoped to determine whether the lake had ‘turned over’ in the fall (i.e. early December), as is characteristic of many lakes, so it was necessary to sample the lake in the winter. The weather was finally favorable Feb. 24th , the depth of the snow had shrunk and the air temperature was close to 0◦C. The ATV didn’t make it very far on the trail and so I want to mention that my son, Linden’s, effort in dragging most of the sampling equipment to the lake and back was greatly appreciated. Mark Conboy (Operations Manager at the Biological Station) had loaned us an ice auger and axe to cut a hole in the ice which was ~18 inches thick as Mark had said to expect. Much to my excitement the temperature of the water in Round Lake was warmest in the bottom 20 to 29 meters. The oxygen also abruptly changed from >3 mg/L in the upper 19 meters; to a low range of 0.56 – 0.43 mg/L in the bottom 9 meters. The temperature profile indicated that the ‘densest’ (4◦C ) cool water in the upper layers, did not mix with the bottom waters (max. 4.7◦C); maintaining the low oxygen environment for the bacterial community. It also suggests that the nutrients at the deep depths are not completely brought back into the water column with a fall or spring ‘turn over’ depriving the phytoplankton of a high nutrient supply. The zooplankton appeared healthy, plump and many were red with hemoglobin in the February samples.
Brocks, J.J., and Schaeffer, P., 2008. Okenane, a biomarker for purple sulfur bacteria (Chromatiacea) and other new carotenoid derivatives from the 1640 Ma Barney Creek Formation. Geochima et Cosmochimica Acta 72: 1396-1414.
Overmann, J. and Pfennig, N. 1992. Buoyancy regulation and aggregate formation in Amoebobacter purpureus from Mahoney Lake. Microbiology Ecology 101: 67-79.
Pfennig,N. and Trüper,H.G. 1989. Anoxygenic phototrophic bacteria. In: Bergey’s manual of systematic bacteriology, Vol 3 (Staley, J.T., Bryant, M.P., Pfennig,N. and Holt, J.G. Eds.) pp.1635-1709. Williams and Wilkins, Baltimore,M.D.
Taylor, D.J., Crease,T.J. and Brown, W.M. 1999. Phylogenetic evidence for a single long-lived clade of crustacean cyclic parthenogens and its implications for the evolution of sex. Proc. R. Soc. London B, 266: 791-797.
It’s no secret that QUBS is a great place for birds and birders alike. Enthusiastic birders visit Opinicon Road every spring to search for species that are at the northern edge of their breeding ranges such as Yellow-billed Cuckoo (Coccyzus americanus), Red-bellied Woodpecker (Melanerpes carolinus), Blue-gray Gnatcatcher (Polioptila caerulea), Yellow-throated Vireo (Vireo flavifrons),
Golden-winged Warbler (Vermivora chrysoptera), Prairie Warbler (Dendroica discolor), Cerulean Warbler (D. cerulea), and Louisiana Waterthrush (Parkesia motacilla). QUBS has also been a hub of avian research for decades, especially for species like Tree Swallow (Tachycineta bicolor), Black-capped Chickadee (Poecile atricapillus), Golden-winged Warbler, Yellow Warbler (D. petechia), Cerulean Warbler, American Redstart (Setophaga ruticilla) and Red-winged Blackbird (Agelaius phoeniceus).
Though the breeding season provides the best birding and is the busiest research season, occasionally interesting and unusual birds show up at QUBS in the winter. This year we’ve had our fair share of notable species including an unseasonable Winter Wren (Troglodytes hiemalis) and a juvenile Golden Eagle (Aquila chrysaetos). But the bird that has attracted the most attention is a Hornemann’s Hoary Redpoll (Carduelis h. hornemanni) which has been visiting bird feeders at QUBS Point on an almost daily basis since February 9, 2011. This 14 g songbird has brought birders from as far away as Pennsylvania, Connecticut, Washington DC and New Jersey. To understand why a Hornemann’s Hoary Redpoll should be so popular among birders it’s necessary to know a thing or two about redpoll taxonomy and natural history.
Redpolls are small finches that breed in the high arctic and subarctic and spend the winter mainly south of the tundra throughout North America and Eurasia. There are two species redpolls in North America, both of which breed in low numbers in northern Ontario and winter in southern Ontario in most years. Redpolls are irruptive during the non-breeding season, which means that in some winters there are lots of redpolls and other winters there are few or none in Eastern Ontario. Annual fluctuations in redpoll numbers are usually correlated with fluctuations in the abundance of food sources, typically birch (Betula spp.) seeds. When seed crops are poor in the boreal forest, redpolls wander south in search of other foods including fodder from birdfeeders.
Whenever redpolls are present, Common Redpoll (C. flammea) is the most abundant species, while Hoary Redpolls (C. hornemanni) are far rarer, so they attract quite a lot of attention from birders when they appear. Both of the redpoll species are comprised of two subspecies (in North America). There is the Southern Common Redpoll (C. f. flammea) and the Greater Common Redpoll (C. f. rostrata); and there is the Southern Hoary Redpoll (C. h. exilipes) and Hornemann’s Hoary Redpoll (there are a wide variety of English names applied to each of these subspecies so it pays to know the scientific names too). The Southern Common and Southern Hoary Redpolls breed across the southern Canadian arctic and subarctic. Greater Common and Hornemann’s Hoary Redpolls breed further north, on Baffin Island, Greenland and in the case of Hornemann’s up to Ellesmere Island! Of the four subspecies, Hornemann’s is certainly the rarest in Ontario. It is only reported in some winters, particularly when there are large irruptions of redpolls.
It’s not uncommon to find both species of redpolls in the same flock, and sometimes three or even all four subspecies can be found together. This winter we’ve recorded all four of the redpoll subspecies at QUBS. Southern Common Redpolls are by far the most numerous with flocks sometimes in excess of 100 birds. Greater Common Redpolls and Southern Hoary Redpolls are seen singly or in pairs within these large flocks. The single female Hornemann’s Hoary Redpoll always appears with other redpolls where it can be easily recognized by comparison with other birds. Compared to the others the Hornemann’s Hoary Redpoll has whiter plumage, less streaking on sides, nearly all-white undertail coverts, more robust head and neck, smaller beak and is noticeably larger.
Its rarity, its size and its extreme northern breeding habitat make Hornemann’s Hoary Redpoll an attractive target for birders, hence the many visitors we’ve received at QUBS in the past two weeks. Redpoll identification can be difficult; in fact it is one of the most challenging identification problems birders face. Direct comparisons between individuals can be helpful and it is necessary to clearly see all field marks in order to properly diagnose which species or subspecies a redpoll belongs to. A good summary of redpoll identification by Ron Pittaway can be found at http://www.jeaniron.ca/2007/Redpolls/redpolltext3.htm.