Successful renesting of Caspian Terns on Mohawk Island, Lake Erie, after complete colony failure Laura E. King and Shane R. de Solla The Caspian Tern (Hydroprogne caspia, island previously provided breeding habi- formerly Sterna caspia) is the world's tat for Common Terns (Sterna hirundo) largest tern and nests globally in dense but their last reported nesting was in 2004 colonies in and around bodies of water. In (Morris 2010), although the species has Ontario, on the Great Lakes, they nest been sighted in 2009 and 2010 flying near regularly on Lakes Huron, Ontario, and the island. Other waterbirds and passer- Erie, generally on islands, peninsulas, or ines (various species of ducks, swallows, protected beaches. Caspian Terns nest on etc.) are sighted on and around the island sand, gravel, or limestone substrates with regularly. little or no vegetation (Ludwig 1965, During the course of our research on Quinn and Sirdevan 1998). At Mohawk Double-crested Cormorants, we visited Island (also known as Gull Island), in east- Mohawk Island several times during the ern Lake Erie between the communities of summers of 2009 and 2010. On 6 June Port Maitland and Lowbanks, a colony 2010, a large seiche (a standing wave in a nests on a beach consisting almost exclu- closed body of water such as a lake) caused sively of crushed Dreissenid (zebra and a nearly one metre rise in water levels in quagga) mussel shells. The earliest record- eastern Lake Erie (Figure 1). Lake Erie is ed colony on Mohawk was 80 pairs in prone to large seiches because of its loca- 1996 (Morris 2010) and since then the tion, shape, and shallow western basin colony has fluctuated between 165 and (NOAA 2003, Litchkoppler 2009). When 441 nests from 2002 to 2009. Mohawk storms blow in from the southwest, as is Island is a federally protected National common, a seiche is set up on the lake, Wildlife Area (NWA) and hosts important and the water from the southwestern end breeding colonies of Double-crested of the lake is pushed towards the north- Cormorants (Phalacrocorax auritus), Her- eastern end. This can temporarily cause ring Gulls (Larus argentatus), and Ring- very high water levels in the northeastern billed Gulls(Larus delawarensis). The end, where Mohawk Island is located. 158 Ontario Birds December 2010 Figure 1. Water levels (rela- 1.4 a. tive to sea level) at Port Col- borne, Ontario, east of Mohawk Island; 1.2 Observed Water (m) a) from 21 May to 20 June 2010; 1.0 b) from 5 June to 7 June 2010. Data from Port Colborne weather buoy 0.8 (42.866667 N, 79.25 W). Canadian Hydrographic Service, Fisheries and 0.6 Oceans Canada. 0.4 22 May 27 May 1 June 6 June 11 June 16 June Date Seiches and often their 1.4 b. June 5 June 6 June 7 associated storms are an important part of the 1.2 Observed Water (m) ecology and structure of the Great Lakes (Trebitz 1.0 2006), moving nutrients to open waters (Bouch - 0.8 ard 2007) and affecting multiple species includ- 0.6 ing mussels (Bowers and de Szalay 2005) and fish 0.4 (Rose man et al. 2001). 12:00 am 12:00 am 12:00 am 12:00 am Before our first trip 12:00 pm 12:00 pm 12:00 pm to the island, we were Date told it had been submerged two days prior nests on the island. We counted 271 (M. Walker, pers. comm.). When we whole or broken tern eggs, but many eggs arrived, we found multiple piles of whole may have been lost, so the number of and broken eggs clustered together from eggs destroyed is likely higher. Any chicks 10 to 20 m from the eastern edge of the that hatched by 6 June would also have island (Figure 2). The tern colony was been also lost. On 8 June, one lone located on the east portion of the island, Caspian Tern chick, newly mobile, ran from about 20 m inland to within 20 cm across the beach at our approach. After from the water’s edge (Figure 3). Given that one day, it was not seen again. Most that the algae mats were washed through- Ring-billed Gull nests and many Herring out the centre of the island, it was appar- Gull nests were also destroyed, as the ent this seiche was high enough to seiche covered muchof the island (Fig- destroy virtually all of the Caspian Tern ure 3). Double-crested Cormorants nest Volume 28 Number 2 159 Figure 2. Caspian Tern eggs destroyed by the 6 June 2010 seiche. 8 June 2010. Photo: Shane de Solla 160 Ontario Birds December 2010 Cormorants Caspian Terns Herring Gulls Ring-billed Gulls extent of flooding washed up eggs lighthouse Figure 3. Approximate location of Caspian Tern (Hydroprogne caspia), Herring Gull (Larus argentatus), and Ring-billed Gull (Larus delawarensis) colonies, with estimated extent of flooding caused by a seiche, 6 June 2010. Modified from Google Earth primarily at the highest elevation of the nests, but no new Herring Gull nests, on island, surrounded by some Herring Gull the days following the seiche. nests, and thus these were largely spared; The ability of a female to lay a new however, some cormorant clutches of late clutch of eggs after the original is des - nests at lower elevations may have been troyed is termed renesting. Renesting is destroyed. During our visits in early June, common to ground nesters, including the terns in the colony were loafing but ducks, coots, turkeys, terns, and gulls, not incubating, and actively foraging who typically face a variety of challenges throughout the day. On 10 June, we such as predation and/or nest destruction observed several pairs of terns mating through changing environments. Terns (Figure 4), and by 6 July, we noticed generally lay one clutch per season, but if many terns sitting in nest dep ressions. clutches and/or chicks are destroyed, ren- That same day, we checked the colony esting can occur. Renesting has been doc- and found that most nest depressions in umented previously in all species of terns, one area contained either one or two eggs. including but not limited to Caspian We counted 361 nests on 8 July and by Terns (Cuthbert 1985, 1988), Least Terns then several chicks had hatched, and by (Sterna antillarum) (Massey and Fancher 15 July many days-old chicks were discov- 1989), Black Terns (Chlidonias niger) ered in nest depressions (Fig ure 5). We (Eichhorst and Reed 1985), and Com- observed a few new Ring-billed Gull mon Terns (Wendelin et al. 2000). Volume 28 Number 2 161 Figure 4. Caspian Tern colony (with Ring-billed Gull colony and Herring Gull in foreground) on Mohawk Island, Lake Erie. The majority of the Caspian Terns are standing, but a few in the foreground can be seen sitting on nests. On the right side of the photo, in the background, a copulating tern pair can be seen. 10 June 2010. Photo: Laura Elizabeth King Caspian Terns on the Great Lakes nests at once due to flooding, the colony often begin to lay eggs around 5 May, can move to a slightly different site with- with young by 1 June (Ludwig 1965). in the general area (Cuthbert 1988), Peak laying period on the Great Lakes which we partially observed in that a por- typically is 7 May–1 June (Cuthbert and tion of the colony moved a short distance Wires 1999). Juveniles then fledge from (approximately 20 metres). Suitable Cas - colonies in July and August; however, lay- pian Tern nesting habitat on Mohawk ing can continue up to the beginning of Island is limited to the eastern-most por- August if renesting is occurring. Our tion of the island, and only on crushed observed colony lost hundreds of eggs, mussel shells. Furthermore, the majority and presumably many chicks, on June 6; of the surrounding territory was occupied if previous research applies to the by Herring or Ring-billed Gulls. If more Mohawk Island colony, it would seem habitat had been available, it is probable that the peak laying period was already that the Caspian Tern colony would have over by the time they lost their nests. moved farther away from the original site When a large number of pairs lose of nest destruction. 162 Ontario Birds December 2010 Figure 5. A view of the new area where Caspian terns nested after the seiche (the smaller, slightly more northern area of the map in Figure 3). More than 20 new nests are seen in this view; days-old chicks can be spotted in more than half of the nests. 15 July 2010. Photo: Laura Elizabeth King Many factors affect renesting, depen - (Arnold et al. 2010). In American Coots d ing upon the individual and the species. (Fulica americana), renesting may be Renesting has been connected with more affected by time and habitat quality female age, nesting experience, body than by the amount of food available to con dition, investment in previous the female. clutch(es), available food, or date Volume 28 Number 3 163 Water levels may also be an important not been performed, but this would be renesting cue (Arnold 1993). In Mallards an interesting area for future studies. (Anas platyrhynchos), renesting is depend- Given that weather is often unpre- ent on variables such as nesting season dictable in the island nesting areas of length, stage of incubation, and date of Cas pian Terns, an adaptation to be able nest loss. There is some evidence that to renest quickly following nest loss is older females and those in better condi- highly advantageous.