Refuge Notebook • Vol. 7, No. 26 • July 8, 2005

A sordid affair: shorebird mating systems by Toby Burke

On a recent outing to Skilak Lake my kids discov- Promiscuity is where males and females, often ered several medium sized shorebirds while walking in groups, consort briefly, mate, and do not form along the lake’s cobbled shoreline. The birds were ap- pair bonds. It occurs regularly in Pectoral and Buff- proximately seven to eight inches long, brown above, breasted Sandpipers as well as Ruffs. The male simply and white below with bold black spotting. They con- fertilizes the female’s eggs and she rears the offspring stantly bobbed their tails or “teetered” while they for- without the male’s assistance. In other mating sys- aged along the lakeshore. When flushed they flew low tems the male may contribute in one or more ways over the water and shoreline with stiff shallow wing such as nest construction or defense; mate, territorial, beats and soft weet, weet, weet vocalizations could be or resource defense; incubation of eggs; or brooding, heard as the birds cavorted about. With this informa- feeding, or defense of young. tion in hand we could readily identify the birds as Spot- It must be noted that in an otherwise monogamous ted Sandpipers. species it is not uncommon to have a regularly oc- The Spotted Sandpiper (Actitis malularia) is a fairly curring minority of polygynous males and conversely common yet often-inconspicuous breeding shorebird there will be a regularly occurring minority of monog- of the Kenai Peninsula typically encountered along the amous pairs among otherwise polygynous species. shorelines of local rivers, lakes, and ponds where it Often a single individual may employ several mat- forages and breeds. While it has the distinction of be- ing systems during the course of their breeding life or ing the most widespread breeding shorebird in North even within a single breeding season depending on en- America its greatest renown is due to its unique mat- vironmental conditions. For example, Snowy Plovers ing system—polyandry, where one female commonly east of the Rocky Mountains are monogamous, both mates with two or more males, sequentially in the male and females attend the nest and together produce Spotted Sandpiper’s case. Polyandry is an uncommon one brood of young per breeding season. West of the mating system occurring in less than one percent of Rockies Snowy Plover females will desert their young bird species worldwide. a few days after hatching while the male remains with Shorebirds as a whole are notable for the va- the brood until they can survive independently. Af- riety and often-complex mating systems they ex- ter deserting the first brood, a third of the females will hibit. Among the 73 species of shorebirds recorded in renest with a new male to establish a second brood. Alaska, as with the majority of bird species worldwide, And after rearing their first brood, half of the males the most common mating system is monogamy, where will renest with a new female to establish their second one male mates with one female and forms a pair bond. brood. The majority of oystercatcher, plover, godwit, curlew, Likewise, Phalaropes, contrary to popular belief, and sandpiper species are principally monogamous. are monogamous the majority of the time. In fact some There are a variety of nonmonogomous mating populations have no documented cases of polyandry. systems employed by shorebirds. Of these the most But in other populations a minority of females, usually common breeding system is polygyny, where one less than 15%, may be polyandrous if there is a sur- male mates with two or more females. White-rumped, plus of available breeding males. Interesting enough Curlew, and Sharp-tailed Sandpipers, for example, in years where climatic conditions are favorable and are polygynous. The counterpart to polygyny is the breeding season is protracted many males may also the uncommonly exhibited polyandry, which is oc- mate a second time with a new female after rearing casionally observed in Red, Red-necked, and Wil- their first brood. son’s Phalaropes and nearly universally in the Spot- Thus while populations of Snowy Plovers and ted Sandpiper. Polygamy is where both polygyny and all three species of phalaropes commonly employ polyandry occur together in the same species. This oc- monogamy as their principal mating system, they curs most frequently in Snowy Plovers. are also known to employ polyandry, polygyny, and

USFWS Kenai National Wildlife Refuge 45 Refuge Notebook • Vol. 7, No. 26 • July 8, 2005 polygamy as opportunities permit. While these four intrigued by the status and distribution of Alaska and species may seem exceptional, with shorebirds there Kenai Peninsula birds and enjoys birding with his wife are many exceptions to the rule. and family. Previous Refuge Notebook columns can be Toby Burke is a refuge biological technician who is viewed on the Web at http://www.fws.gov/refuge/kenai/.

46 USFWS Kenai National Wildlife Refuge