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Observations of a Killdeer Nest with Possible Simultaneous Polygamy
Chuck Slusarczyk Jr. and Andrew W. Jones

Northeastern Naturalist, Volume 24, Issue 4 (2017): N35–N37

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N35 2017 Northeastern Naturalist Notes Vol. 24, No. 4 C. Slusarczyk Jr. and A.W. Jones Observations of a Killdeer Nest with Possible Simultaneous Polygamy Chuck Slusarczyk Jr.1 and Andrew W. Jones2,* Abstract - Shorebirds (Order Charadriiformes) exhibit a wide variety of breeding systems, and have been the subject of extensive studies on the evolution of these systems. Nevertheless, there are many monogamous species within this clade. Previous studies of Charadrius vociferus (Killdeer) have shown that they are monogamous, with only a single documented variation (serial polyandry). We report observations at a nest that contained 7 eggs (typical nests have 4 eggs). The nest was being attended by 3 adults, and it successfully fledged young. This is the first documented Killdeer nest with possible simultaneous polygamy. Breeding systems vary between species of birds as a result of various life-history tradeoffs and evolutionary conflicts between the sexes (Thomas et al. 2007). Although birds display a wide diversity of breeding systems, the majority of species are monogamous. However, examples of all forms of polygamy have been documented in avian species (Oring 1982). The breeding systems of shorebirds (Order Charadriiformes, often called waders) are well studied and they include examples of all of the breeding system types. Additionally, the various forms of polygamy are more commonly seen within this order than in other avian orders (Thomas et al. 2007). There are conflicting explanations for this situation. Initial hypotheses on breeding-system variation in shorebirds focused on the fact that most species have fixed-size clutches. Most Northern Hemisphere shorebirds lay 4-egg clutches. Oring (1986) reviewed the literature on avian polyandry, noting that a fixed-size clutch may be an ancestral condition that leads to polyandry as individuals try to maximize their own reproductive output; however, Thomas et al. (2007) suggested flaws in this explanation. Charadrius vociferus L. (Killdeer) is a familiar North American shorebird species that nests in open fields, including many human-modified landscapes. They are known to be monogamous, with no documentation of extra-pair copulations (Jackson and Jackson 2000). Here we present observations at a nest with 7 eggs that was being attended by 3 adults. On 2 July 2016, C. Slusarczyk Jr. discovered a Killdeer nest with 7 eggs at Burke Lakefront Airport near downtown Cleveland, Cuyahoga County, OH. The nest was being tended by 3 adult birds. Slusarczyk continued to observe the nest through 31 July 2016 when there were no more eggs, nor nestlings, present. Typically, Killdeer are socially monogamous (the male and female demonstrate a pair bond, though they may also seek extra-pair copulations), and, like all shorebirds, their first clutch of the year has 4 eggs (Jackson and Jackson 2000). Killdeer construct a nest as a scrape in an open field, typically lined with pebbles and other black and white debris, which helps camouflage the eggs (Jackson and Jackson 2000). This nest was situated in a wide-open graveled area ~50 m from the east wall of an airport hangar, in a fully sunlit location and on level ground. It was constructed primarily of pea- to marble-sized gravel, with the larger pieces placed towards the periphery of the scrape. Overall, the nest was ~0.33 m in circumference and well camouflaged. The field 12154 Thurman Avenue, Cleveland, OH 44113 2Department of Ornithology, Cleveland Museum of Natural History, 1 Wade Oval Drive - University Circle, Cleveland, OH 44106. *Corresponding author - ajones@cmnh.org. Manuscript Editor: Daniel M. Keppie Notes of the Northeastern Naturalist, Issue 24/4, 2017 2017 Northeastern Naturalist Notes Vol. 24, No. 4 N36 C. Slusarczyk Jr. and A.W. Jones Figure 1. Killdeer nest with 7 eggs at Burke Lakefront Airport in Cleveland, Cuyahoga Co., OH. The nest already had 7 eggs when first discovered. (A) Initially, the outer eggs were not neatly arranged; narrow ends of the eggs are oriented in haphazard directions. (B) After 4 July, the eggs were configured with 1 egg in the center and the other 6 arranged around it with their narrow ends facing the middle egg. Eggs remained in this configuration during successive observations. Both photos by Chuck Slusarczyk Jr. (left on 2 July 2016, right on 23 July 2016). where the nest was constructed was a mosaic of bare gravel and low plants. The nest itself was in an area where low-growing Trifolium repens L. (White Clover), Plantago lanceolata L. (Narrowleaf Plantain), and Plantago major L. (Broadleaf Plantain) were dominant and a few grasses were present. Two sheets of weathered commercially manufactured 1.2 x 2.4-m (4 x 8-ft) plywood lay within 2 m of the nest. Burke Lakefront Airport has a high density of breeding pairs (C. Slusarczyk Jr., pers. observ.). Chuck Slusarczyk Jr. also observed 5 other nests within ~250 m that had the expected 4-egg complement. The nest already contained 7 eggs when discovered (Fig. 1A). We observed 3 adults displaying in close association with the nest (within 3 m). The eggs were arranged in a circle of 6 with 1 additional egg in the center; they remained in this orientation on all successive visits. Initially, the outer 6 eggs were poorly arranged, with the pointed ends in various directions. By 4 July, the outer eggs were oriented in the more typical arrangement for shorebirds, with all points oriented towards the center of the nest (Fig. 1B). In all successive 15 observations, all 3 birds performed distraction displays within 5 m of the nest. Shorebirds, and particularly Killdeer, are well known for their various behaviors to redirect potential predators away from their nests, including brooding a site where there are no eggs, feigning a wing injury while calling, and running aggressively at predators with body feathers erect and both wings and tail spread open to appear larger (Jackson and Jackson 2000). C. Slusarczyk Jr. observed all of these behaviors, and kept observations as short as possible to avoid undue disturbance while documenting this unusual nest. Killdeer have a 22–29-d incubation period (Jackson and Jackson 2000). Without knowing the date that the eggs were laid or when incubation began, C. Slusarczyk Jr. kept a careful watch on the eggs almost daily in late July (daily visits were not possible due to access issues at this site). On 25 July, the 3 adults became more vocal, their displays became more frantic, and they approached within 5 m of the observer. On 27 July, 2 Killdeer chicks were visible scurrying into the clover, and 2 additional freshly hatched birds were resting on the remaining 3 eggs while 3 adults vocalized and displayed nearby. No additional observations were made until 30 July 2016, when a single egg remained and multiple (uncountable) young were in the area. On 31 July 2016, no eggs remained. N37 2017 Northeastern Naturalist Notes Vol. 24, No. 4 C. Slusarczyk Jr. and A.W. Jones Jackson and Jackson (2000) reviewed the literature on Killdeer and noted several reports of 5 or 6 eggs in a nest, and a single report of 8 eggs. They overlooked a report by Mundahl et al. (1981), which documented a Killdeer nest with 20 eggs. The 2 adults associated with the latter nest were marked with ink on the feathers. The marked birds were observed copulating, and several eggs were tested and shown to be fertile. No other individual adult Killdeer were observed at the nest, and the authors suggested that the 20 eggs were all laid by a single female. A single adult could only incubate ~6 eggs and, in this case, none of the eggs hatched. Brunton (1988) studied Killdeer in Michigan, and followed a pair that nested successfully. The day after their 4 eggs hatched, the female was observed mating with another male on an adjacent territory, and 4 days later, researchers discovered a nest with 3 eggs. This situation is an example of sequential polyandry; the female did not associate with both males at the same time. In the nest we report here, the 3 adults were not banded or otherwise marked. We did not directly observe mating and we did not collect the birds; thus, we do not know whether there were 2 females laying eggs in the single nest, or if two males were socially bonded to a single female. Both possibilities are plausible, considering the fecundity of the female in the Mundahl et al. (1981) report and polyandrous behavior reported in Brunton (1988). Thomas et al. (2007) advocate incorporating the availability of potential mates into expanding our understanding of breeding-system evolution. In the present case, Killdeer were very abundant (but not counted), and access to a large pool of possible mates may have played a significant role in this possible polygamous nesting. For future studies of intraspecific variation in mating systems of shorebird species and other clades thought to be socially monogamous, incorporating DNA sampling may reveal much more flexibility in breeding systems than is presently documented. Acknowledgments. A. Jones was supported by the William A. and Nancy R. Klamm Endowment at the Cleveland Museum of Natural History. Literature Cited Brunton, D.H. 1988. Sequential polyandry by a female Killdeer. Wilson Bulletin 100:670–672. Jackson, B.J., and J.A. Jackson. 2000. Killdeer (Charadrius vociferus). In P.G. Rodewald (Ed.). The Birds of North America. Cornell Lab of Ornithology, Ithaca, NY. Available online at https:// birdsna-org.bnaproxy.birds.cornell.edu/Species-Account/bna/species/killde/. Accessed 5 February 2017. Mundahl, J.T., O.L. Johnson, and M.L. Johnson. 1981. Observations at a 20-egg Killdeer nest. The Condor 83:180–182. Oring, L.W. 1982. Avian mating systems. Pp. 1–92, In D.S. Farner, J.R. King, and K.C. Parkes (Eds.). Avian Biology. Volume VI. Academic Press, New York, NY. 490 pp. Oring, L.W. 1986. Avian polyandry. Current Ornithology 3:309–351. Thomas, G.H., T. Székely, and J.D. Reynolds. 2007. Sexual conflict and the evolution of breeding systems in shorebirds. Advances in the Study of Behavior 37:279–342.