147 Suspected Nest Usurpation of a Spotted Sandpiper by a Common Tern

Colin Lake

On 25 June 2003, I was part of an island in the northwest basin of Ontario Ministry of Natural Lake Abitibi, part of the Lake Resources (OMNR) field crew col­ Abitibi Islands Provincial Nature lecting data on waterbird nesting Reserve (UTM E 577943, N populations on the islands and 5420247), in Ontario Breeding Bird shoreline of Lake Abitibi, Atlas square 17NQ71. In order to Cochrane District. The survey was understand the factors which may designed to locate and count nests have contributed to the mixed in colonies previously identified clutch, a brief survey of the litera­ from aerial surveys. In a small ture follows. Common Tern (Sterna hirundo) colony of 22 nests, I photographed a NESTING BIOLOGY nest with an unusual complement It is not uncommon to find these of eggs (Figure 1). The nest con­ two species nesting adjacent to one tained a total of seven eggs. Three another in Common Tern colonies. eggs were identified in the field as Sandpipers (Scolopacidae), Plovers Common Tern, and the remaining (Charadriidae) and other shore­ four obviously belonged to another birds are known to actively seek out species. Consultation with various nest locations within Common Tern experts determined that the nest colonies so that they may take was constructed by a Spotted advantage of the Common Terns' Sandpiper (Actitis macu!arius), aggressive nest defense behaviour based on the nest size and building (Oring et al. 1997, Lauro and material. Furthermore, the four Tanacredi 2002). smaller eggs were positively identi­ Spotted Sandpipers nest near fied as those of a Spotted water, preferring some cover from Sandpiper. The Common Tern had herbaceous vegetation (Oring et al. apparently been the latecomer, lay­ 1997). Nesting generally occurs from ing its eggs in the nest after the mid May to early July. Nests are con­ sandpiper. Although adults of both structed of dead grass and small species were observed in the vicini­ woody material, and are approxi­ ty of the colony, none were obvious­ mately 12 cm in diameter when fin­ ly attending the nest. ished (Oring et al. 1997). Clutches The colony was located on a generally contain four eggs, but suc­ small, sparsely vegetated bedrock cessfully incubated clutches of five

VOLUME 22 NUMBER 3 148 have been observed (Smith 1932). 0.35 % of 2000 nests (Nisbet) Common Terns nest on low ele­ checked during laying (in Rohwer vated sites, generally near water (O­ and Freeman 1989). A survey of the S m above high-water mark), with literature failed to turn up any slightly higher sites being preferred reported instances of interspecific and occupied by early arriving birds nest parasitism concerning (Nisbet et al. 1984). Nest sites near Common Terns, either as host or patchy vegetation are preferred parasite. Similarly, Spotted Sand­ (Nisbet 2002), as they provide pipers are reported to experience important sources of cover for intraspecific brood parasitism chicks (Burger and Gochfeld 1990). rarely «10/0), and only two Nesting occurs from late April to instances of interspecific parasitism early June (Nisbet 2002). The male (both by Brown-headed Cowbirds, initiates nest building at several Molothrus ater) were observed dur­ sites until the female chooses an ing 19 years of fieldwork (Dring et acceptable site for egg deposition. al. 1997). Common Terns and Once incubation begins, both par­ Spotted Sandpipers rarely experi­ ents gradually add to the nest, the ence supernumerary clutches due material varying with availability to intraspecific or interspecific nest near the nest, including sticks, peb­ parasitism, and the observed mixed bles and shells. The diameter of the species clutch was not likely due to completed nest is variable depend­ this behaviour. ing on construction material, aver­ aging 18 cm (Nisbet 2002). Clutch Egg Dumping % size is usually three eggs (90 ), Egg dumping differs from para­ although rarely four or more sitism, in that it refers to atypical (Nisbet 2002). laying behaviour, rather than a cal­ culated reproductive strategy. Nest Parasitism Wiens (1971) predicted that egg Nest parasitism is the intentional dumping can occur in three situa­ laying of eggs in the nest of another tions: when nest destruction occurs bird without contributing to incuba­ immediately prior to, or during, egg tion or care of the young. The host laying; by accidental placement of and parasite can be the same eggs; or with inappropriate syn­ species (intraspecific parasitism) or chronization of nest building and different species (interspecific para­ laying. Egg dumping, then, can sitism). Intraspecific nest parasitism occur in any species that finds itself has been documented in 234 bird in unusual or unfavourable nesting species (Yom-Tov 2001). Intraspeci­ situations. Sealy (1989) described a fic nest parasitism in Common case of "incidental egg-dumping" Terns has been observed rarely, e.g., by a House Wren (Troglodytes 0.150/0 of 4000 nests (Burger) and aedon) into a Yellow Warbler ONTARIO BIRDS DECEMBER 2004 149

(Dendroica petechia) nest, and containing eggs. They observed a referred to other cases of egg pair of Common Terns providing dumping by species which appeared care to three Black-winged Stilt to be anomalies, rather than inten­ chicks and speculated that the tional nest parasitism. Mixed Black-winged Stilt nest was either clutches have resulted in situations found abandoned or the Common where unrelated species had similar Terns forcefully evicted the original nesting requirements that were in occupants, then incubated the eggs short supply. This was hypothesized and "adopted" the chicks. They fur­ to be the case when an American ther speculated that the terns, once Kestrel (Falco sparverius) pair suc­ incubating the stilt nest, could not cessfully hatched a Bufflehead identify the original eggs as foreign, (Bucephula albeola) egg (Dawson as the two species have eggs that and Bortolotti 1997). Both species are similar in size and colour. Saino are cavity nesters, possibly resulting and Fasola (1993) reported that in competition for nest sites and the Common Terns do not discern their unintentional egg dumping inci­ own eggs from foreign ones. The dent. As mentioned earlier, nest I found on Lake Abitibi Common Tern and Spotted appears to agree with this state­ Sandpiper have similar nesting ment. Were the CommonTerns able preferences and timing, and per­ to discern their own eggs from haps a high local density of those of the original nest occupant, Common Tern nests and limited the sandpiper eggs likely would desirable nest sites influenced the have been ejected from the nest, nesting sequence in the Lake rather than remaining with the Abitibi nest. Fournier (2000) sug­ newly added tern eggs. The mixed gested that a combination of fac­ species clutch suggests that the tors, including island nesting, colo­ Common Terns accepted all the nial nesting behaviour and high eggs in the nest as their own. Paz densities of birds resulted in a and Eshbol (2002) also observed mixed nest of scaup (Aythya sp.) Common Terns evicting other and Ring-billed Gull (Larus species (terns, stilts, and Avocets, delawarensis). These conditions Recurvirostra avosetta) from nests, exist on Lake Abitibi, and may have but did not report on whether these contributed to the observed nest. usurped nests also contained eggs. Midura et al. (1991) reported a Interspecific Nest Usurpation by Least Tern (Sterna antil/arum) Common Terns usurping a nest containing three Paz and Eshbol (2002) described an Piping Plover (Charadrius inferred case of Common Terns melodus) eggs. The Least Tern usurping a Black-winged Stilt added two of its own eggs, then suc­ (Himantopus himantopus) nest cessfully incubated all five. The VOLUME 22 NUMBER 3 150 young plovers were removed and mating system in which one female placed with other Piping Plover mates sequentially with up to four adults by the researchers, so subse­ males, each of which cares for a quent observations regarding clutch and a brood, usually alone brooding were not made. (Gring et al. 1997). The single male The cases reported in Paz and sandpiper would likely not have Eshbol (2002), along with the Lake been able to fend off the intruding Abitibi observation, suggest that terns, which are known for their Common Terns will occasionally aggressive behaviour. Pickett et al. appropriate and lay eggs in the (1988) found that Spotted nests of shorebird species. Sandpiper males were significantly more protective during the brood­ Discussion ing period than they were during Unfortunately, the Lake Abitibi incubation, when the Common Tern Common Tern colony was not visit­ deposited its eggs into the nest. ed on subsequent days, so no fur­ Either the tern forced the sand­ ther information about the nest was piper off the nest, or found the nest gathered. For example, were the recently abandoned, then laid its eggs being actively incubated, how eggs in the nest. This raises the many hatched, and if any hatched, question of why the Common Tern was there any evidence of "adop­ female accepted a previously con­ tion" of the Spotted Sandpiper structed nest with a full clutch of young by the Common Tern adults? another species' eggs, despite the Based on the evidence suggesting fact that nest parasitism is so rarely that the Common Tern pair were observed in the species. latecomers, and the Spotted Assuming that the terns were Sandpiper was the original occu­ incubating the eggs normally, it is pant and builder of the nest, some possible that the eggs ofboth species speculations can be made. hatched. The equivalent clutch vol­ Possibly, the tern pair arrived at ume of the observed nest (four the colony late, finding the prefer­ Spotted Sandpiper eggs plus three able nest sites occupied. Common Common Tern eggs) was approxi­ Terns are reported to have relative­ mately 96 ml, equivalent to a clutch ly high colony-site fidelity over sea­ of 4.8 Common Tern eggs (tern egg sons, and fledge more young per volume from Nisbet 2002; Spotted nest in larger, denser colonies than Sandpiper egg volume calculated in smaller less dense colonies after Hoyt 1979). Common Terns (Karwowski et al. 1995). Perhaps have been reported incubating four for these reasons, the usurping terns or more eggs, albeit rarely (Nisbet were reluctant to settle for another 2002), and therefore, it is possible less-populated nesting site. Spotted that both species in the clutch could Sandpipers exhibit a polyandrous have been incubated successfully. ONTARIO BIRDS DECEMBER 2004 151

Figure 1: Spotted Sandpiper nest with a full clutch of Spotted Sandpiper eggs and Common Tern eggs, located in a small Common Tern colony, Lake Abitibi, Ontario, 2S June 2003. Photo by Colin Lake. Once hatched, Spotted Sandpiper per individual chick (less food, chicks are somewhat more precocial poorer vigilance against predators) than Common Tern young, and may by the Common Terns, and subse­ be expected to benefit from their quently lower fledging rates. The foster parents' aggressive defense of Lake Abitibi nest and aforemen­ young and perhaps survive to fledge. tioned literature suggest that terns However, behavioural differences can occasionally obtain supernu­ caused problems for the adoptive merary clutches via nest usurpation Common Tern parents and Black­ behaviour. Common Tern adults winged Stilt chicks reported in Paz that adopted foreign chicks in addi­ and Eshbol (2002), including the tion to their own brood were chicks not accepting food and not thought to be displaying maladap­ responding to danger calls made by tive behaviour (Saino et al. 1994) by the adoptive terns. Ultimately, all of incurring higher than normal the adopted Black-winged Stilt parental effort costs. This presumed chicks died by 10 days of age, appar­ cost associated with increased ently due to inappropriate parent­ brood size might explain why offspring interactions between the Common Terns do not usurp nests two species. as a rule, even though they certain­ Presumably, an extra large ly have opportunity to do so in most brood would result in poorer care high-density colonial nesting sites. VOLUME 22 NUMBER 3 152

In the observed nest, it appears that the note, providing contacts and the terns obtained a nest site at the review of early drafts. Mark Peck potential cost of increased parent­ (Royal Ontario Museum), Don ing duties. It would be interesting to Sutherland (OMNR) and George know whether any young (of either Peck (Ontario Nest Records species) successfully fledged in this Scheme) all gave freely oftheir expe­ instance, or if this unusual situation rience, identifying the nest and eggs proved too taxing on the apparent­ in the photo. Pete Cott (Department ly unwitting adoptive parents. of Fisheries and Oceans) provided helpful suggestions on an early draft. Acknowledgements Ed Morris and Mick Gauthier I would like to thank Ken Abraham (OMNR) were co-workers during (OMNR) for first suggesting I write the Lake Abitibi fieldwork.

Literature Cited Burger, J. and M. Gochfeld. 1990. Early Nisbet, I.C.T., J.M. Winchell, and A.E. Heise. experience and vegetation preferences in 1984. Influence of age on the breeding Common Tern chicks. Wilson Bulletin 102: biology of Common Terns. Colonial 328-333. Waterbirds 7: 117-126. Dawson, R.D. and G.R. Bortolotti. 1997. Oring, L.W., E.M. Gray, and J.M. Reed. 1997. Misdirected incubation in American Spotted Sandpiper (Actitis macularia). In Kestrels: A case of competition for nest The Birds of North America, No. 289 (A. sites? Wilson Bulletin 109: 732-734. Poole and F. Gill, editors). Academy of Fournier, M.A. 2000. Incidents of mixed Natural Sciences, Philadelphia, Pennsyl­ clutches among scaup and Ring-billed vania, and American Ornithologists' Union, Gulls. Waterbirds 23: 114-116. Washington, D.C. Hoyt, D.E. 1979. Practical methods of esti­ Paz, U. and Y. Eshbol. 2002. Adoption of mating volume and fresh weight of bird Black-winged Stilt chicks by Common eggs. Auk 96: 73-77. Terns. Wilson Bulletin 114: 409--412. Karwowski, K., J. E. Gates, and L.H. Pickett, P.E., S.J. Maxson, and L.W. Oring. Harpers. 1995. Common Terns nesting on 1988. Interspecific interactions of Spotted navigational aids and natural islands in the Sandpipers. Wilson Bulletin 100: 297-302. St. Lawrence River, New York. Wilson Rohwer, F.C. and S. Freeman. 1989. The dis­ Bulletin 107: 423--436. tribution of conspecific nest parasitism in Lauro, B. and J. Tanacredi. 2002. An exami­ birds. Canadian Journal of Zoology 67: nation of predatory pressures on Piping 239-253. Plovers nesting at Breezy Point, New York. Saino, N. and M. Fasola. 1993. Egg and nest Waterbirds 25: 401--409. recognition by two tern species Midura, A.M., S.M. Beyer, and H.J. (Sternidae:Aves). Ethology, Ecology and Kilpatrick. 1991. An observation of Evolution 4: 467--476. human-induced adoption in Piping Saino, N., M. Fasola, and E. Crocicchia. 1994. Plovers. Journal of Field Ornithology 62: Adoption behaviour in little and common 429--431. terns (Aves; Sternidae): Chick benefits and Nisbet, I.C.T. 2002. Common Tern (Sterna parents' fitness costs. Ethology 97: hirundo). In The Birds of North America, 294-309. No.618 (A. Poole and F. Gill, editors). The Sealy, S.G. 1989. Incidental "egg dumping" Birds of North America, Inc., Philadelphia, by the House Wren in a Yellow Warbler Pennsylvania. nest. Wilson Bulletin 101: 491--493.

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Smith, G.A.1932. A Spotted Sandpiper incu­ Yom-Tov, Y. 2001. An updated list and some bates five eggs. Wilson Bulletin 44: 38. comments on the occurrence of intraspe­ Wiens, J.A. 1971. 'Egg-dumping' by the cific nest parasitism in birds. Ibis 143: Grasshopper Sparrow in a Savannah 133-143. Sparrow nest. Auk 88: 185-186.

Colin Lake, Management Biologist, Lake Ontario Management Unit, Ontario Ministry of Natural Resources, Glenora Fisheries Station, R.R. 4, 41 Hatchery Lane, Picton, Ontario KDK 2TD

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