135 Foraging Behavior of Long-tailed Ducks in a Ferry Wake Matthew C. Perry* Abstract - Clangula hyemalis (Long-tailed Ducks) were observed diving in the wake of the Nantucket Island ferry during December over a 5-year period (2005–2009). The unusual diving behavior appeared to be related to foraging, but could not be confirmed. Long-tailed Ducks typically feed on more mobile prey than most other diving ducks, and it is speculated that the propeller wash in shallow water dislodged or disturbed prey and provided an enhanced feeding opportunity. Long-tailed Ducks collected while feeding in a disturbed area near a clamming boat not far from the ferry channel were feeding predominantly on Crangon septemspinosa (Sand Shrimp) that apparently had been dislodged by the clamming operation. Casual observers are aware that birds can be attracted to boats to receive food. There are many reports of marine birds attracted to boats and ships to feed on organisms captured by the vessels or wastes coming from these vessels (Dare 1982, Griffiths 1982, Hudson and Furness 1988). However, there are few reports of birds responding to natural foods made available by the vessel’s propeller wash (Camphuysen 1996, Eades 1982). While traveling the 46 km (29 mi) from Hyannis, MA, to Nantucket Island, MA, on the 6:15 AM and 9:15 AM Nantucket ferries (M/V Eagle) during December, 2005–2009, I observed an unusual behavior of Clangula hyemalis L. (Long-tailed Duck; LTDU) in close proximity to the stern of the ferry. Within 15–20 minutes of leaving the wharf in Hyannis, I noticed LTDUs that were flying into or near the wake of the ferry and then diving within a short time period after landing on the water. The ducks typically flew in from both sides of the ferry and initially appeared to be mostly coming from areas in front of the ferry. I presumed that the ducks were merely displaced as the ferry moved through the channel, until I realized that many ducks were coming from long distances on both sides of the channel and were focused on landing in or a short distance from the vessel’s wake. This behavior occurred for approximately 30–45 minutes while traveling on the mainland side of the ferry channel (Fig. 1). During the 5 years I made observations on approximately 500 ducks, I estimated that a distance of 31 m (100 ft) was the closest the ducks came to the ferry while landing in the channel, 231 m (750 ft) was the farthest, and that most ducks landed within 62–108 m (200–350 ft) of the ferry. Approximately 70% of ducks landed within the wake of the ferry, with the remaining 30% landing outside the wake and up to 62 m (200 ft) from the side of the wake. Ducks landing within the wake typically landed facing the center of the wake, and ducks landing outside on either side typically faced the wake. The direction that ducks were facing on landing appeared to be irrespective of wind conditions, but related to the location of the ferry wake. Long-tailed Ducks typically feed in small groups (Mudge and Allen 1980), which was observed with ducks landing in the ferry wake. Sizes of flocks were recorded in December 2008 and 2009, while on the 9:15 AM ferry from Hyannis, and the data were similar to casual records of the previous 3 years. Out of 69 individual flocks, 32 (46%) were single ducks, and the other flocks ranged from 2 to 6 ducks (Table 1). The sex ratio was skewed toward males, with all single ducks being males and flocks of 2 or 3 individuals having a maximum of 1 female, and some flocks with no females. The number of females ranged *USGS Patuxent Wildlife Research Center, 12100 Beech Forest Road, Laurel, MD 20708; mperry@usgs.gov. Notes of the Northeastern Nat u ral ist, Issue 19/1, 2012 136 Northeastern Naturalist Vol. 19, No.1 from 1–3 ducks in flocks of 4–6 ducks. A male-skewed sex ratio is commonly seen in other wintering areas for LTDUs (Robertson and Savard 2002) and also for other diving duck species (Haramis et al. 1994). Ducks typically dove shortly after landing on the water, with the delay time ranging from 1 to 20 seconds and an average delay time of 5.1 seconds. In most cases, it appeared Table 1. Flock size and time delay before Long-tailed Ducks dove after landing on water during observations in December 2008 and 2009. Time on water before diving Flock size Number (%) Range (sec.) Mean (sec.) 1 32 (46) 1–20 5.7 2 17 (25) 1–10 5.7 3 8 (12) 3–7 4.9 4 4 (6) 4–6 4.8 5 6 (9) 1–8 3.6 6 2 (3) 2–11 6.5 Totals 69 1–20 5.1 Figure 1. Location of unusual foraging along ferry route (A), and area where Long-tailed Ducks were collected for food habits study (B). 2012 Northeastern Naturalist Notes 137 that, when present, the female dove first and the male immediately followed her, possibly indicating a dominant role of the female on wintering areas, which also exists on breeding areas (Alison 1975). It is unknown how long ducks remained under water, as no ducks were observed resurfacing, suggesting that they were underwater for relatively long periods. Dive time varies by depth, location, and season, but has been recorded at over 90 seconds in winter (Robertson and Savard 2002). It is likely that my observations of LTDUs landing in or near the wake of the ferry and immediately diving were related to an enhanced feeding opportunity. I speculate that the strong wake of the ferry disturbed the bottom enough to cause prey to be more available to the ducks. I suggest that this is due to disturbance of the bottom by the propeller wash, whereby mobile benthic organisms are moved into the water column or to the bottom surface and become available as prey. The only organism apparent in the wake was an unidentified Rhodophyta—possibly Palmaria palmata (L.) Kuntze (a red alga) that was disturbed from the bottom of the channel, as it was not observed in the water on either side of the channel. This presumed foraging behavior of the ducks in the ferry channel was only seen on the mainland side of the Sound and was never observed on the Nantucket Island side or in the middle of Nantucket Sound (Fig. 1). This is most likely due to the depth of the channel. The area where ducks were attracted to the ferry was in the range of 5–10 m (15–30 ft) and thus it was likely that the bottom was disturbed by propeller wash, whereas much of the rest of the channel is 10–15 m (30–45 ft), too deep for the bottom to be directly affected. In December, most of the estimated 200,000 to 500,000 LTDUs (Christmas Bird Count data) that winter in the Nantucket Sound area go to the ocean south of Nantucket at dawn and return to the Sound at dusk (Davis 1997, Perkins 1988). The ducks observed from the ferry apparently have a novel feeding strategy, but represent a small percentage of the total population in Nantucket Sound. Ducks in the ocean are feeding predominantly on Gammarus annulatus S.I. Smith (pelagic amphipods; White et al. 2009). It is possible that LTDUs observed in the ferry wake were also feeding on pelagic amphipods, although these organisms are much more abundant in the ocean (Avery et al. 1996). If the LTDUs are foraging, they are more likely feeding on mobile benthic organisms such as shrimp, isopods, or clam worms dislodged by the propeller wash and in motion in the water column for only brief periods. Numerous other avian species were in or near the ferry channel and were disturbed by the advance of the ferry, but none displayed the behavior of the LTDUs. Other species present included Melanitta perspicillata L. (Surf Scoter), M. fusca L. (White-winged Scoter), M. americana Swainson (Black Scoter), Somateria mollissima L. (Common Eider), Gavia immer Brunnich (Common Loon), Gavia stellata Pontoppidan (Red-throated Loon), Morus bassanus L. (Northern Gannet), Mergus serrator L. (Red-breasted Merganser) , and 3 species of gulls (Larus marinus L. [Great Black-backed], L. argentatus Pontoppidan [Herring], and L. philadelphia Ord [Bonaparte’s]). The fact that other diving seaducks (scoters and eiders) did not exhibit this behavior possibly suggests that the prey may have been mobile, which are typically more often sought by the fast swimming LTDUs when compared to other seaduck species (Perry et al. 2007). The focus of LTDU on the wake and the rapid diving upon arrival indicates a learned behavior similar to the behavior of Alle alle L. (Little Auk) feeding in the propeller wake of ferries arriving and departing a port in the Netherlands (Camphuysen 1996). Larus minutus Pallas (Little Gull) have been observed feeding on the water surface on food apparently generated from a propeller wash of ships in Liverpool Bay, UK (Eades 1982). Although the learned behavior of the LTDUs, Little Auks, and Little Gulls is a human-generated phenomenon, there are examples of seaducks being responsive to novel natural foraging 138 Northeastern Naturalist Vol. 19, No.1 opportunities. Surf Scoters have been observed in Puget Sound, Washington, feeding in areas where Eschrichtius robustus Lilljeborg (Gray Whales) have disturbed benthic habitat (Anderson and Lovvorn 2008). Large numbers of LTDUs have been observed feeding on possibly disturbed benthic organisms in a swift current over an upwelling area in the Saguenay River in Quebec (Robertson and Savard 2002). Seaducks also respond to ephemeral prey, as with Surf Scoters feeding on Ophyryotrocha sp. Benidorm (polychaetes; Lacroix et al. 2005) and Clupea pallasi Valenciennes in Cuvier and Valenciennes (Pacific Herring; Lewis et al. 2007) in British Columbia. In February 2010, a total of 9 LTDUs were collected while feeding around a boat that was clamming near Roger’s Shoal, Nantucket Sound, approximately 1.6 km (1 mile) west of Monomoy Point (Fig. 1). These ducks were observed very close to the wake of the clamming boat and dragline. Analyses of the gizzard and gullet (P. Osenton, USGS Patuxent Wildlife Research Center, Laurel, MD, pers. comm.) revealed that the food was both soft-and hard-bodied benthic organisms that may have been disturbed by the dragline. Crangon septemspinosa Say (Sand Shrimp) was a dominant food in this sample of ducks, and these likely were disturbed by clamming. Feeding activity near the clam boat was similar to activity of LTDUs observed diving in the wake of the ferry, as the ducks were diving close to the dragline shortly after flying to the area. Unfortunately, the organisms that the LTDUs might have been feeding on in the ferry wake cannot be ascertained without the collection of ducks. This sampling would be extremely difficult to do for reasons of safety and public relations, and therefore, I can only speculate that the unusual behavior observed was related to foraging on organisms generated by the ferry wake. Acknowledgments. Technical and editorial comments were provided by A. Berlin, K. Blackshaw, K. Boone, S. Boyd, D. Forsell, L. Garrett, R. Kennedy, V. Laux, G. Olsen, P. Osenton, S. Perkins, E. Ray, R. Therrien, and T. White. Literature Cited Alison, R.M. 1975. 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