The two largest rails in the United States are so similar in appearance and vocalizations that they have at times been considered a single species. In general the King Rail is a more brightly-colored bird of freshwater marshes, while the Clapper is a duller bird of coastal salt marshes.
But even this statement requires a few caveats. For one thing, Gulf Coast Clappers are brighter than East Coast Clappers, and the disjunct populations of “Light-footed” and “Yuma” Clappers in California and Arizona are brighter still, bright enough to have been considered subspecies of King Rail by some authors. Furthermore, King and Clapper Rails have been known to hybridize in brackish marshes where their ranges meet, spawning the dreaded “Cling Rails” — birds presumably intermediate in all respects, and not safely identified in the field, even when you can see them — which is not very often, for these ghosts of the cattails.
Most of the time, the presence of one of these rails is announced solely by their loud, unmusical calls, leaving us to identify them solely by voice. It isn’t always possible, but today we’ll talk about when and how it can be done.
The “Kek” Series
For humans, this vocalization is about as exciting as listening to a six-year-old incessantly rap a stick against a wooden fence. For female rails, it must be quite an aphrodisiac, because it’s the primary way that males attract mates in early spring. It’s typically heard for a fairly brief period out of the year, and given only rarely after the singer is paired.
Male Kings and male Clappers “sing” with the same notes — the key to identifying them is to listen to the speed of their calls. Here’s a useful snippet from the Sibley Guide to Birds:
a series of unmusical kek notes, slower at beginning and end; the tempo of the fastest portion is useful for species identification. [...] Individuals may give faster or slower calls depending on mood, but such departures are usually brief. Long, consistent bouts of typical calls can be reliably identified.
According to Sibley, eastern Clapper Rails “kek” at about 4-5 notes per second, while Kings are slower, usually 2 notes per second. In a careful survey of all the rail recordings I could find online, I found the differences to be consistently smaller than this. I found some very excited Clappers reaching 5 notes per second, but an extended listen to most birds will find them averaging between 3 and 4 notes per second in the fastest parts of their series.
Kings, meanwhile, seem to average between 2 and 3 notes per second.
But even they can get up pretty far into Clapper speed if they feel particularly motivated. I’m assuming this one is safely called a King, since it was recorded just outside Columbus, Ohio:
It’s clear that fast Kings overlap with slow Clappers (or is it that excited Kings overlap with bored Clappers?). However, I agree with Sibley’s basic point: an extended listen to a bird should provide, at least, a good strong clue to its identification.
You are more likely to hear this vocalization than the “Kek” Series. It’s given by both sexes almost year-round, as a pair contact call and as a way of mediating territorial disputes with other pairs. Any loud noise may set off a Grunt Series, and one grunting rail often sets off another. Mated pairs may perform extended, unsynchronized grunt duets, one starting slightly after the other, in one of nature’s least aesthetically pleasing romantic gestures. These duets tend to go on longer than solo versions, and are less likely to accelerate at the end.
The Grunt Series of the two species, like the “Kek” Series, are made of similar notes and are best distinguished by speed. Again the Clapper is the faster bird, and again I’ve found there to be more overlap between the species than reported in Sibley: Clappers appear to average 4-6 notes per second, while Kings clock in at 3-5 notes per second. This range of overlap is great enough to suggest that only the fastest of Clappers and the slowest of Kings are safely identifiable by this call.
In the 1980s, Richard Zembal and Barbara Massey were the first to discover the meaning of this sound. They were observing two color-banded pairs of “Light-footed” Clapper Rails in California. One morning, one of the males was killed by a Red-tailed Hawk. Two days later, his mate (#421) began giving the “Kek-burr” call. By that same evening, she had succeeded in stealing the sole remaining male (#443):
From 1723 to 1843 that first evening they clappered [grunted] in duet 12 times and were seen copulating twice. The newly abandoned female, #442, began to kek-burr on the following morning. During that day and the following one, #443 divided his time between the two females. Without the aid of a full-time mate, #421 abandoned her nest. Each of the females, once alone, eventually kek-burred when #443 was with the other one, and #443 responded every time by returning to the calling female, often quickly. We witnessed #443 respond to kek-burring 11 times in 36.1 h of observations over 4 days. During one exchange he traveled the 190 m to the calling female within 18 min of the onset of kek-burring. When another male appeared on the fourth day, #443 returned to #442, #421 settled in with the new arrival making use of the same nest), and kek-burring ceased.
Thus, Zembal and Massey concluded that the “Kek-burr” is the female’s equivalent of the “Kek” Series — her way of advertising a burning urge to mate.
Females of both species give nearly identical “Kek-burr” calls, and I do not know of any way to separate the species by this call. Excited birds may give many rapid “Keks” before the burr; in some situations, the burr is given separately.
This is the vocalization that Sibley refers to as “a raucous squawk like a startled chicken”. It’s not quite clear what motivates this call, but in both species it varies from a grunt to a squeak, and there do not appear to be any significant differences between the two species’ versions.
This rarely-heard call is apparently given by alarmed rails near the nest. There are very few recordings of this sound, but you can hear the hoot of a Clapper Rail here. Meanwhile, this recording at the Macaulay Library may represent the hoot of King Rail, but the bird making the sound was not seen, so it’s not even certain that the sound was made by a rail.
If you can shed any light on the mysterious Macaulay recording from Florida, or on the hooting calls of rails in general, please let me know. If you’ve got recordings, I’d love to hear them.
I just learned about recent research into the King/Clapper Rail complex: a 2012 Ph.D. dissertation by James Maley that not only found a solid genetic distinction between King and Clapper Rails (further demonstrated by this recent paper), but also found that West Coast “Clapper Rails” are part of a distinct lineage that also includes the tenuirostris “King Rails” of central Mexico. All these are separate from the longirostris group in South America. Caribbean birds cluster with North American Clapper Rails.
Thus, it seems there’s a good case not only for keeping King and Clapper Rail separate, but further splitting Clapper Rail into 3 or 4 species. In both proposals, we’d end up with 3 species of large rail in North America: King, “eastern” Clapper, and “western” Clapper. See the recent discussion on BirdForum for a little more info.