Reporting Guidelines – Fish and American Crow
Ken Burrell, Natural Resource Solutions Inc.
April 16th, 2021
The expansion of Fish Crow into Ontario has brought about identification challenges for birders throughout the province. Fish Crow was historically considered an extremely rare vagrant in Ontario; however, since 2012, the species has undergone a rapid expansion into the province. The most likely route of expansion is by way of the Finger Lakes region of upstate New York (NY) where a resident population of Fish Crows has been present since the late 1970s (Wells and McGowan 1991). The species has also expanded up the Mississippi River valley (e.g. Hicks 2009), which cannot be discounted as a possible source of Ontario birds, especially those showing up occasionally in the extreme southwest of the province.
Figure 1. Suspected core breeding range of Fish Crow in Ontario.
Since 2012 and the rapid expansion of Fish Crows into Ontario, increasing evidence of breeding has been noted primarily in the Niagara area and between Toronto and Burlington. The first documented nest was reported in 2018 (Fazio 2019) and current evidence suggests they may be breeding in various areas in close proximity (i.e. within 1 km) of the Niagara River and Lake Ontario shoreline from the Niagara area, through Hamilton and Toronto and possibly as far east as Oshawa. There have been scattered breeding season records outside of this “core” area where they should be watched for as well.
When to Atlas
In southern Ontario, American Crows typically initiate their breeding territory establishment starting in about mid-March. During this time, crows will vocalize frequently throughout their territories and while adults are on the nest incubating eggs. Eggs are laid as early as late March in southern Ontario and incubation lasts about 17 days with young typically hatching in late April to mid-May. Fledging occurs typically around late May but can last through the end of July in rare cases. (Dates and durations from Peck and James (1987), Rousseu and Drolet (2015), and Verbeek and Caffrey (2020)).
In the Ithaca, NY population, Fish Crows tend to nest about two to three weeks later than American Crows (McGowan 2020), and this timing matches the documented 2018 nest in Mississauga (Fazio 2019).
Visual ID Challenges
Fish Crow and American Crow are virtually identical visually, with visual cues that make differentiating between the two species very challenging, if not downright impossible to observe. On average, Fish Crows weigh 50-70% that of American Crows; however, this size difference can be hard to judge unless the two are side-by-side and is complicated by sexual size dimorphism in both species (males are larger than females). Fish Crows can also be glossier in appearance and have slightly more ‘petite’ bills. There are several other minute plumage differences, such as primary formula, which are best outlined in Kevin McGowan’s detailed overview: https://www.birds.cornell.edu/crows/FishCrow.htm
Figure 2. Fish Crow from Mississauga, Peel Region. Photograph by Dennis Dirigal.
The best – and most reliable – way to differentiate Fish and American Crows is through their vocalizations.
American Crow vocalizations are best characterized by their familiar “caw-caw” call which can be given clearly or harshly. Examples of their range of calls can be found on Xeno-Canto, the Macaulay Library, and the Peterson Guide to Bird Sounds. Here is an example of a typical American Crow call sequence, starting with clear “caws” followed by harsher “caws” from a second bird in the background:
Fish Crow vocalizations are characterized as being much more nasal in quality, with single calls best described as “uhn” or “awh”; however, their two-part “uh-uh” call is most distinctive. Examples of their range of vocalizations can also be found on Xeno-Canto, the Macaulay Library, and the Peterson Guide to Bird Sounds. Here is an example of a typical Fish Crow giving mainly single note calls (note American Crow “caws” in background for comparison):
And here is an example of the double “uh-uh” call:
While American and Fish Crows are readily differentiated by their typical calls, beware of the American Crow begging call given by dependent young and adults in some situations, which can sound similar to Fish Crow. Adult American Crows will give begging calls early in the breeding season (typically early April to mid-May), when adults are at or close to their nest and are responding to their mates. Dependent young American Crows will also frequently give begging calls to their parents, once they have left the nest (late May to July) and are begging for food. An example of an American Crow begging call can be found on Xeno-Canto here:
As a general rule, take a precautionary approach with all silent crows encountered within the narrow geographic band where Fish Crows are now readily found (see Figure 1). All silent crows in this region should be recorded as “Crow species”. Silent crows observed throughout the rest of the province can be recorded as American Crow.
Fazio, L. 2019. First successful nesting of Fish Crow in Ontario and Canada. Ontario Birds 37: 100-106.
Hicks, T.L. 2009. Fish Crow (Corvus ossifragus) Range Expansion in Kansas. Kansas Ornithological Society Bulletin 60: 29-36.
McGowan, K. J. (2020). Fish Crow (Corvus ossifragus), version 1.0. In Birds of the World (A. F. Poole and F. B. Gill, Editors). Cornell Lab of Ornithology, Ithaca, NY, USA. https://doi.org/10.2173/bow.fiscro.01
Peck, G.K. and R.D. James. 1987. Breeding Birds of Ontario Nidiology and Distribution Volume 2: Passerines. Royal Ontario Museum, Toronto, Ontario. 387 pp.
Rousseu, F. and B. Drolet. 2015. Prediction of the nesting phenology of birds in Canada. In: J. Hussell and D. Lepage. 2015. Bird Nesting Calendar Query Tool. Project NestWatch. Bird Studies Canada / Études d’Oiseaux Canada, URL: https://www.birdscanada.org/apps/rnest/warning.jsp
Verbeek, N. A. and C. Caffrey (2020). American Crow (Corvus brachyrhynchos), version 1.0. In Birds of the World (A. F. Poole and F. B. Gill, Editors). Cornell Lab of Ornithology, Ithaca, NY, USA. https://doi.org/10.2173/bow.amecro.01.
Wells, J.V. and K.J. McGowan. 1991. Range expansion in Fish Crow (Corvus ossifragus) the Ithaca, NY, colony as an example. Kingbird 41:73-81.
Thanks to Laura Hockley of Natural Resource Solutions Inc. for the preparation of the map in Figure 1.