Group Bathing by Shorebirds, Gulls, and Terns

William E. Davis, Jr.

October 1, 2020 8 MIN READ Feature Articles

Bathing by Ruddy Turnstones, Sanderlings, and Short-billed Dowitchers

On March 3, 2020, I was watching a group of approximately 50 shorebirds, mostly Ruddy Turnstones but also a few Sanderlings that were present on the dock. At about 5:30 pm, a group of 30-plus flew down beside the dock into water three to four inches deep and—with all of the birds standing facing the incoming small waves—began a bathing frenzy (Figure 1). They dipped their heads below the surface, partially submerging their bodies, and flapped their wings wildly in what was clearly a bathing sequence. Bathing was followed by extensive preening. This behavior continued for about five minutes, after which the flock returned to the dock. Perhaps the outgoing tide, which lowered the water three to four inches beside the dock, triggered the bathing response in these shorebirds. It was my impression that all of the birds in this flock bathed at some point, although not all the birds bathed together at any point in time.

Figure 2. This flock of mostly Short-billed Dowitchers bathed and preened.

On March 14 at 4:03 pm, a flock of about 70 Sanderlings stood in or beside shallow water as the flats began to emerge on the outgoing tide. A second group of Sanderlings and a few more scattered among a separate group of about 30 Ruddy Turnstones brought the Sanderling total to more than 100. At least a dozen Sanderlings and a few turnstones were actively bathing. Over approximately 20 minutes, I estimated that nearly all the birds had bathed and were actively preening. The birds were facing into the wind and incoming waves. The following afternoon at 5:05 pm, a flock of about 50 shorebirds, mostly Ruddy Turnstones, but including a few Sanderlings, were bathing near the dock. Almost all the shorebirds had bathed and preened by 5:15 pm. Two days later around 3:45 pm, about 50 turnstones and Sanderlings had come down to bathe and, all neat and clean, flew back up to the dock. The pattern of late afternoon group bathing was repeated at 5:35 pm when about 20 turnstones and Sanderlings bathed together and again at 6:00 pm when a small group of Ruddy Turnstones bathed near the dock.

On March 31 shortly after 5 pm, I noticed about 30 shorebirds in a bathing frenzy just off the right side of the dock. It was a dynamic flock, with new birds joining the bathers every few seconds and others returning to the dock. Most of the bathing birds were Sanderlings or Ruddy Turnstones. A Royal Tern (Thalasseus maximus) bathed with the flock of shorebirds and another Royal Tern and a Sandwich Tern (Thalasseus sandvicensis) bathed to the right of the flock. At 6:12 pm, a flock of 30-plus shorebirds, mostly Short-billed Dowitchers (Limnodromus griseus) were on the water; about a half dozen dowitchers bathed and the remainder preened, suggesting that they had already bathed (Figure 2).

On April 16 at 5:54 pm, a group of about 20 Sanderlings and Ruddy Turnstones flew down from the dock and bathed for about five minutes. At 6:38 pm, a larger group of 30-plus shorebirds bathed near the dock. The group included Sanderlings, turnstones, and dowitchers and was somewhat dynamic, with birds from the bathing group flying to the dock and switching places with birds that had been on the dock originally (Figure 3). On April 21 at 12:55 pm when the flats were emerging in the falling tide, I watched a Ruddy Turnstone bathing beside three others that were furiously preening and doubtless had bathed. About 10 feet away, a Sanderling bathed for about five minutes and a second bird joined it. At 5:50 pm, a single Sanderling bathed. By 6:00 pm, most of the shorebirds were gone as the incoming tide began to cover the flats. The following day, six Sanderlings were bathing in a pool at 2:19 pm and five Sanderlings bathed at 2:23 pm in a different pool. At 4:10 pm, I noticed seven dowitchers. One was bathing and the others were preening and had probably just finished bathing. At 6:30 pm, 10 dowitchers bathed in one pool and 14 Ruddy Turnstones bathed nearby in two other pools.

Figure 3. Short-billed Dowitchers, Ruddy Turnstones, and Sanderlings group bathe.

The literature on bathing Ruddy Turnstones is sparse. They are "fond of bathing in shallow water, fluttering vigorously" (Nettleship 2020), but no reference was made to group bathing behavior. No reference is made to Sanderlings bathing in the Birds of the World (formerly Birds of North America) account (Macwhirter et al. 2020), but I had no difficulty finding photos of bathing Sanderlings on Google. The literature on bathing by Short-billed Dowitchers is more extensive, "Bathing most common in evening (18:00—19:00), when feeding in small ponds with other species. After bathing flutters to dry place, bares oil gland, and preens" (Jehl et al. 2020). Again, no reference is made to group bathing. All of my observations of bathing occurred in late afternoon suggesting that bathing may be a usual end-of-day event. The exact timing of the large group bathing episodes was strongly influenced by the tide cycle because there appears to be an optimal water depth on the flats for bathing.

Figure 4. One Whimbrel is partly submerged and is bathing. A Willet watches the group.

A Whimbrel and a Willet Bathe

On April 18 at 5:03 pm, four Whimbrels (Numenius phaeopus) alit in the shallow water near two Willets. The Willets walked away but one stopped about 10 feet from the Whimbrels. At 5:30 pm, one of the Whimbrels began to bathe, dipping its head and bill under water, dipping its front and rear body in a rocking motion, fluffing, and shaking its tail side to side. A Willet watched (Figure 4). The other Whimbrels preened. The nearby Willet began to bath at 5:37 pm, apparently stimulated by the Whimbrel bathing and the others preening. Willets commonly bathe in groups (Davis 2016, Lowther et al. 2020). The Whimbrels preened their lower backs near the oil gland, chin-scratched, shook their heads, and fluffed. They preened until 5:46 pm, when they all flew away. The Birds of the World Whimbrel account (Skeel and Mallory 2020) reports only that "Fall migrants occasionally bathe in tidal streams on Cape Cod." These birds were spring migrants.

Figure 5. Our dock attracts Royal Terns, Laughing Gulls, and other species.

Small Group Bathing by Royal, Sandwich, and Least Terns, and Laughing Gulls.

During daylight hours, as many as 30 Royal Terns (Thalasseus maxima) and a dozen Laughing Gulls (Leucophaeus atricilla) roosted on the dock at our rental house. The dock also hosted a small number of other species, including Sandwich Terns (Thalasseus sandvicensis) (Figure 5). There were no Least Terns (Sternula antillarum) during March but they arrived in April and the dock hosted more than 20. At low tide, substantial rocky, algae-coated substrate is exposed, but is entirely covered by water from mid to high tide. On 16 days from March 12 through April 22, I saw at least one tern or gull bathing near the dock. The bathing was communal for most of the gulls and terns. In most cases, the bathing occurred in two to three inches of water near the end of the dock. In all cases, the birds stood facing into the wind and waves.

Most of the instances of bathing involved multiple birds. The groups would be dynamic, with some birds joining the bathing group as other birds finished bathing and left the water. On March 12 at about 2:30 pm, I noticed several Royal Terns bathing next to the dock as the tide dropped. They partially submerged their bodies, then dipped their heads and bills, with bills held straight out, under water while flapping wings, body feathers extended. A few minutes later two more terns, which had been standing nearby, began bathing. A fifth tern then dropped in for a bath after several of the bathing terns had returned to the dock. Slightly farther up the dock two Laughing Gulls—one an immature—bathed, poking their heads under water, bills pointed down, and fluttered their wings and tails in much the same way the terns did. My notes of these observations say: "Water depth seems to be the key in triggering this bathing response in terns and gulls."

Figure 6. Five Royal Terns and six Laughing Gulls bathe together.

On March 15 between 4:05 and 4:49 pm, I observed 12 Royal Terns and two Laughing Gulls bathing during a 44-minute period. On March 16 at 6:05 pm, five Royal Terns and six Laughing Gulls bathed together next to the dock (Figure 6). On March 31 at 5 pm, a Royal Tern bathed with a flock of shorebirds and another Royal Tern and a Sandwich Tern bathed at the right side of the flock. Eventually eight Royal Terns joined the bathing group.

Least Terns were not seen in the area until March 28 and not more than a dozen at a time until April 13. There were about 20 Least Terns, three of them bathing, on the flats on April 17 at 3:40 pm when the incoming tide began to submerge the flats. Soon, six Least Terns were bathing at once, dipping into the water, fluffing and wing-flapping with bodies partially submerged (Figure 7). When finished, they walked or flew to the exposed flats and preened with other terns. I estimated from the number of preening terns that at least a dozen terns had bathed. On April 21, a Least Tern was bathing in a pool on the tidal flats when a second tern flew in and joined it. A third bird joined the two bathers. The first bird left the water and stood on the exposed flats and preened; it was soon followed by a second, leaving one tern bathing. Several minutes later, a fourth tern joined the bathing tern. This sequence of one tern leaving the water to preen and another bird joining the remaining bather continued until five Least Terns had bathed.

Figure 7. Six Least Terns are bathing and many more are preening.

Bathing in gulls and terns appears to be an afternoon, particularly a late afternoon, phenomenon. On the 16 days during which I recorded gulls or terns, the earliest bathing occurred at 2:30 pm and the latest at 6:05 pm. The tide cycle also may have contributed to the optimal water depth near the dock for bathing. Bathing occurred during both the rising and falling tide, although most instances were during the falling tide.

Bathing in gulls and terns is well known, although perhaps under-reported. The Birds of the World account of the Royal Tern states, "Bathes in groups in shallow water" (Buckley and Buckley 2020). The account for Laughing Gull reports, "Individuals bath singly or in small groups in both fresh and salt water…." and continues with a description of the bathing behavior, referencing it to Stone 1937 (Burger 2020). The Sandwich Tern account (Shealer et al. 2020) mentions "group bathing in tidal pools adjacent to colonies" and describes the behavior. The account of the Least Tern (Thompson et al. 2020) states "At colonies, regularly uses salt or fresh water for bathing. Individuals normally bathe alone but may be joined by 2–10 other birds…" and then describes the characteristics of the bathing procedure. I could find no reference to group bathing in mixed-species flocks, as was the case with a Sandwich Tern bathing with a Royal Tern, a Royal Tern bathing with a flock of shorebirds, and Royal Terns bathing with Laughing Gulls as described above. In summary, it appears that bathing by these species is a common occurrence, biased heavily toward the end of the day, and not restricted to the areas adjacent to breeding colonies or to the breeding season.

Conclusions

I conclude: (1) bathing is common in shorebirds, gulls, and terns; (2) for the species studied here, group bathing, or the tendency toward group bathing is the norm; (3) watching other birds bathe is an incentive to join the bathing group, in many cases leading to interspecific group bathing; (4) bathing for the bird species in this study is primarily an afternoon, end-of-day phenomenon; (5) preening normally follows bathing and can be considered a stage in the bathing procedure; and (6) the timing of bathing is influenced by water depth, and therefore is often influenced by the tide cycle.

Literature Cited

• Buckley, P. A., and F. G. Buckley. 2020. Royal Tern (Thalasseus maximus), Version 1.0. In Birds of the World (S. M. Billerman, Editor.). Cornell Lab of Ornithology, Ithaca, New York.
• Burger, J. 2020. Laughing Gull (Leucophaeus atricilla), Version 1.0. In Birds of the World (P. G. Rodewald, Editor.). Cornell Lab of Ornithology, Ithaca, New York.
• Davis, W. E. Jr. 2016. Shorebird Behavior on their Wintering Grounds. Bird Observer 44: 266–269.
• Jehl, J. R. Jr., J. Klima, and R. E. Harris. 2020. Short-billed Dowitcher (Limnodromus griseus). In Birds of the World (A. Poole and F. B. Gill, Editors.). Cornell Lab of Ornithology, Ithaca, New York.
• Lowther, P. E., H. D. Douglas, III, and C. L. Gratyto-Trevor. 2020. Willet (Tringa semipalmata), Version 1.0. In Birds of the World (A. F. Poole and F. B. Gill, Editors.). Cornell Lab of Ornithology, Ithaca, New York.
• Macwhirter, P., P. Austin-Smith, and D. E. Kroodsma. 2020. Sanderling (Calidris alba), Version 1.0 in Birds of the World (S. M. Billerman, Editor). Cornell Lab of Ornithology, Ithaca, New York.
• Nettleship, D. N. 2020. Ruddy Turnstone (Arenaria interpres). Version 1.0. In Birds of the World (S. M. Billerman, Editor). Cornell Lab of Ornithology, Ithaca, New York.
• Shealer, D., J. S. Liechty, A. R. Pierce, and M. A. Patten. 2020. Sandwich Tern (Thalasseus sandvicensis), Version 1.0. In Birds of the World (S. M. Billerman, Editor.). Cornell Lab of Ornithology, Ithaca, New York.
• Skeel, M. A., and E. P. Mallory. 2020. Whimbrel (Numenius phaeopus), Version 1.0. In Birds of the World (S. M. Billerman, Editor.). Cornell Lab of Ornithology, Ithaca, New York.
• Stone, W. 1937. Bird Studies at Old Cape May: An Ornithology of Coastal New Jersey. Philadelphia, Pennsylvania: Delaware Valley Ornithological Club.
• Thompson, B. C., J. A. Jackson, J. Burger, L. A. Hill, E. M. Kirsch, and J. L. Atwood. 2020. Least Tern (Sternula antillarum), Version 1.0. In Birds of the World (A. F. Poole and F. B. Gill, Editors.). Cornell Lab of Ornithology, Ithaca, New York.