Walking in on a point is always an exciting experience, especially in an area where multiple upland game birds occur. It’s a bit of Christmas morning surprise with each flush. In the ruffed grouse and American woodcock range you might be tipped off on what species to expect by the presence of what looks like white paint sloshed from a can: woodcock splash! This fascinating fecal phenomenon has some interesting physiological and evolutionary origins.
All organisms produce some sort of nitrogen-based byproducts of metabolism (life sustaining chemical reactions) that the organism cannot use. Nitrogen is associated with the consumption (or eating) of proteins. If these nitrogen byproducts accumulated in the organism they would become toxic. Hence the need for an excretory system to remove them from the body. This process also requires the presence of water, either metabolic or consumed, to occur. Most mammals, with few exceptions, excrete urea as their nitrogenous waste (in urine).
Fish and other aquatic organisms, for which water is not a limiting resource, tend to excrete ammonia — a far more toxic nitrogenous waste. This excretion is via highly diluted urine or through the gills. Reptiles, depending on habitat (aquatic or terrestrial) might excrete ammonia or uric acid. Birds, regardless of habitat association, primarily excrete uric acid. Of all the nitrogen wastes this white, crystalline paste, requires the least amount of water to produce and gives most bird droppings their characteristic white color.
Uric acid is excreted by birds in a semi-solid suspension with nitrogen concentrations which are orders of magnitude greater than those of the most efficient mammals (e.g. kangaroo rats). In short, it takes far less water to flush the nitrogenous waste from birds than it does for terrestrial mammals. Since weight reduction is critical for flight, birds have many weight-reducing adaptations (e.g. hollow bones supported by lightweight internal struts). A reduction in water weight is one of those important adaptations.
Birds concentrate uric acid in their cloaca (the single opening for reproduction and excretion of waste characteristic of birds) before defecation to levels of concentration up to 3,000 times that of the concentration of their blood (as compared to some of the most efficient mammals that can only achieve 20-30 times that concentration). Therefore, birds require less water to excrete their waste, therefore carrying less water weight.
A bird’s diet gives a good prediction of the amount of uric acid that might be produced and excreted. For example, grouse eat a mainly plant-based diet with some proteins (except for summer). Therefore, the droppings of these birds tend to have a fair amount of plant matter and a round cross shape in cross section with a white cap that is associated with the leading end of the dropping (i.e., as the dropping leaves the cloaca, it pushes that accumulated uric acid along with it).
In contrast, species that eat a diet high in protein (insectivorous or carnivorous), tend to have predominantly white and shapeless droppings. Hence the term woodcock splash which is a shape associated with fluid falling from some distance onto a surface. Carnivorous birds like owls and hawks, along with primarily insectivorous birds, like woodcock, tend to have white runny droppings.
So, the next time you are in the autumn woods and come across the telltale sign of woodcock splash, you might find yourself appreciating it more than simply knowing which species it came from.
To learn about finding and identifying woodcock habitat check out: How to Identify American Woodcock Habitat
Last modified: November 12, 2018