Photo from Ducks Unlimited https://www.ducks.ca/species/ruddy-duck

Part I – General Information and ID

Description and ID

The Ruddy Duck (Oxyura jamaicensis) is a small species of diving duck belonging to the Anatidae family in the order Anseriformes. Learning to identify waterfowl can be a dubious task but there are certain traits that can help in the case of the Ruddy Duck.

1. Size
2. Does it dive or dabble?
3. Can you see its tail?
4. Is it sleepy?

Ruddys are quite small at 300-850 grams compared to the well-known Mallard’s hefty 1000-1300 grams (All About Birds Ruddy Duck; All About Birds Mallard). Still, Ruddy ducks have been described as “very chunky” which may explain their nickname “butterball” (Johnsgard 2010 pp. 530, 529). They are stocky, with a small frame and a thick neck. Without a direct comparison it can be difficult to tell the size of a bird, so instead, look at its behaviour; does it dive or dabble? Ruddy Ducks dive fully underwater to find their meals while dabbling ducks, like Mallards, tip upside-down, keeping their back half above the water to eat. So, if you see a duck butt sticking up in the air, it most likely does not belong to a Ruddy duck.

Photo of a dabbling Mallard by Emma Wallace-Tarry

These inconspicuous ducks are typically silent and often “lethargic” (Audubon). Ruddy Ducks are more active at night and are often observed sleeping during the day. This might make it hard to use the other identifying behaviours, but if you see a really sleepy duck, it’s worth considering that it’s a Ruddy.

Plumage

The distinguished male breeding plumage is only present in late spring and summer (Johnsgard 2010). Otherwise, look for the clear white cheek patch in the non-breeding male, which is streaked with brown in females. Telling apart immature males from females is left to the experts…

Habitat and Range

The Ruddy Duck is the most abundant stiff-tailed duck in North America (Johnsgard 2010). In British Columbia, Ruddy Ducks can be found breeding in the interior or wintering along the coast (Johnsgard 2010). Their range includes southern Canada from west to east and almost all of the US and Mexico (All About Birds). The main breeding ground is central North America, with about 86% of the breeding population in the prairie pothole region (All about birds Ruddy Duck). A Ruddy Duck’s preferred breeding location will have marshy areas containing open water (fresh or alkaline) and dense plants upon which they can build their nests (Johnsgard 2010). In the winter they are partial to brackish bays and other coastal areas but still frequent wetlands (All about birds Ruddy Duck).

Breeding and Behaviour

Ruddy ducks are unique among ducks for their breeding behaviour. Despite their innocent appearance, males are known for being aggressive and promiscuous (Brennan et al. 2017). Unlike most other ducks, they only pair up once reaching the breeding grounds and the partnerships are very short (All about birds Ruddy Duck; Brennan et al. 2017). They experience intense sexual competition and many males often battle for the attention of one female (Brennan et al. 2017). The unique mating display of the male ruddy duck is shown in the video below.  

Eggs and Nesting

Ruddy Ducks lay the largest eggs (proportional to body size) of all waterfowl (All About Birds Ruddy Duck). They sometimes engage in parasitic egg laying, by laying eggs in the nests of other birds of their own or other species (Audubon). Fortunately for their victims, the young require little care as they are fairly developed at hatch (Audubon).

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Part II – Research

Photo of a White-Headed Duck by Otgonbayar Tsend https://macaulaylibrary.org/asset/94227671

The Ruddy Duck has an unfortunate history in Europe. The species was introduced to the UK in the 1950s and soon established populations in multiple European nations (Robertson et al. 2015). The already endangered White-Headed Duck, a stiff-tailed European relative of the Ruddy Duck, had its population further reduced due to interbreeding between the species (Robertson et al. 2015). A cull began in the 1980s to kill all Ruddy Ducks and Ruddy/White-Headed Duck hybrids in an attempt to rescue the native species (Robertson et al. 2015). By the year 2000, there were approximately 6,000 Ruddy Ducks in the UK (Robertson et al. 2015) but that number was brought down and in 2021, it was reported that there were likely 10-15 Ruddy Ducks remaining in the UK (Brown 2021). White-Headed Duck numbers in Europe increased from just 22 individuals in 1977 to over 2,500 individuals in 2021 (Brown 2021). Things may have settled down in Europe, but there is some concern that Ruddy Ducks might begin a similar takeover in the Caribbean by outcompeting another of their relatives, the masked duck (Goodman et al. 2019).

Photo from Ducks Unlimited https://www.ducks.ca/species/ruddy-duck/

As mentioned in the ID section of this blog, the bill of a male ruddy undergoes a colour change from dark brown to pale blue in preparation for breeding. This may have left you curious as to how this happens. In many bird species, ducks included, the males molt and acquire flashier plumage for the breeding season. In male ruddy ducks, this occurs during a prealternate molt in the spring, through which they acquire their distinctive “ruddy” (or rufous) colour (Pyle 2005). Pigment deposition in feathers is controlled, at least in part, by hormones (Pyle 2005). But what if it’s not feathers that are changing colour, and what if the colour doesn’t come from a pigment?

The colour blue, like the sky-blue bill of a male Ruddy Duck in breeding plumage, is typically a structural colour in birds. Structural colours are seen in bare parts of birds (like legs, bills, and the skin around the eye) as well as in plumage. Structural colours are produced when light reflects off microscopic structures in tissues; in bare parts (like the bill) this would likely be collagen fibers (Price-Waldman & Stoddard 2021).

Research on the exact mechanism of bill colouration in Ruddy Ducks was difficult to find, but a paper by Hays and Habermann from 1969 describes the dissection of Ruddy Duck bills. They discovered that there was, indeed, no blue pigment, confirming that the blue colour we see is structural. They found a layer of black, which they determined to be the brown or black pigment, melanin, beneath a thin surface layer (Hays and Habermann 1969). They elucidated that some structural characteristic of the surface layer and/or the melanin beneath it resulted in the blue colouration (Hays and Habermann 1969). But how does the bill change from brown to blue and back again?

Studies have found that bare parts of birds can change colour much quicker than plumage (Iverson & Karubian 2017), which makes sense considering that feathers must be moulted and then replaced to induce a colour change. In fact, the cere (the fleshy upper part of the bill in some species) can change colour within seconds in male Crested Caracaras; but the colour in this case comes from hemoglobin, not a structural colour (Iverson & Karubian 2017).

Lahaye et al. (2014) did an interesting experiment with female budgerigars where they found that structural colour on bare parts (in their case ceres) of the bird could cause relatively quick colour changes in response to testosterone. Exactly how testosterone does this doesn’t seem to be well understood but Lahaye et al. (2014) advised that it may alter the microscopic structures in the skin, or affect the pigments present in the skin, resulting in a colour change (pp. 9). They suggested that “[testosterone] may cause a withdrawal of melanin from the outer tissue layers of the cere, revealing the potential underlying blue structural color” (Lahaye et al. 2014 pp. 9).

In Ruddy Ducks, an influx of testosterone might result in the removal of melanin from the subsurface of the bill, leading to the expression of the blue structural colour. This seems to agree with the results from Hays and Habermann’s dissection of Ruddy Duck bills. There is abundant research on mechanisms of colouration in avian plumage but there seems to be significantly less on the colours of bare parts, specifically on the structural colouration of bare parts. Hopefully there is more to come.

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Thank you for taking the time to read my blog.

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References

All About Birds. (n.d.) Mallard. https://www.allaboutbirds.org/guide/Mallard/

All About Birds. (n.d.) Ruddy Duck. https://www.allaboutbirds.org/guide/Ruddy_Duck/overview

Audubon. (n.d.) Ruddy Duck. https://www.audubon.org/field-guide/bird/ruddy-duck

Brennan P. L. R., Gereg. I., Goodman, M., Feng, D., & Prum, R. O. (2017). Evidence of phenotypic plasticity of penis morphology and delayed reproductive maturation in response to male competition in waterfowl. The Auk, Vol. 134 (4), pp. 882-893. https://www.jstor.org/stable/90014208

Brown, P. (2021, Dec 22). Specieswatch: 10 to 15 ruddy ducks left in UK after Europe-wide cull. The Guardian. https://www.theguardian.com/environment/2021/dec/22/specieswatch-10-to-15-ruddy-ducks-left-in-uk-after-europe-wide-cull#:~:text=Peak%20numbers%2020%20years%20ago,Oxyura%20leucocephala%2C%20of%20southern%20Spain.  

Goodman, N. S., Eitniear J. C., & Anderson, J. T. (2019). Time-activity budgets of stiff-tailed ducks in Puerto Rico. Global Ecology and Conservation, 19. https://doi.org/10.1016/j.gecco.2019.e00676

Hays, H., & Habermann, H. M. (1969). Note on Bill Color of the Ruddy Duck, Oxyura Jamaicensis Rubida. The Auk, Vol. 86 (4) pp. 765-766. https://digitalcommons.usf.edu/auk/vol86/iss4/34

Iverson, E. N. K., & Karubian, J. (2017). The role of bare parts in avian signaling. The Auk, Vol 134 (3) pp. 587-611. https://academic.oup.com/auk/article/134/3/587/5149285

Johnsgard, P. A., “Waterfowl of North America: Stiff-Tailed Ducks, Tribe Oxyurini” (2010). Waterfowl of North America, Revised Edition (2010) by Paul A. Johnsgard. 14. https://digitalcommons.unl.edu/biosciwaterfowlna/14

Lahaye, S. E., Eens, M., Darras, V. M., & Pinxten, R. (2014). Bare-part color in female budgerigars changes from brown to structural blue following testosterone treatment but is not strongly masculinized. PLoS One. Vol 9 (1) pp. 1-11.  https://pmc.ncbi.nlm.nih.gov/articles/PMC3901734/ .

Price-Waldman, R., & Stoddard M. C. (2021). Avian Coloration Genetics: Recent Advances and Emerging Questions. Journal of Heredity, Vol 112. (5) pp. 395-416. https://academic.oup.com/jhered/article/112/5/395/6272461

Pyle, P. (2005). Molts and Plumages of Ducks (Anatinae). Waterbirds Vol. 28 (2), pp. 208-219. https://doi.org/10.1675/1524-4695(2005)028[0208:MAPODA]2.0.CO;2

Robertson, P.A., Adriaens, T., Caizergues, A., Cranswick, P. A., Devos, K., Gutiérrez-Expósito, C., Henderson, I., Hughes, B., Mill, A. C., & Smith, G. C. (2015). Towards the European eradication of the North American ruddy duck. Biological Invasions, Vol 17, pp. 9–12. https://doi-org.ezproxy.viu.ca/10.1007/s10530-014-0704-3