William E. Davis, Jr.
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Figure 1. The foraging cormorant, moving left, has its head and body nearly submerged. Photographs by the author.
On April 7, 2020, I was watching Double-crested Cormorants (Phalacrocorax auritus) forage near the dock at our rental house at 1455 Long Beach Drive, Big Pine Key, Florida, and noticed shallow-water foraging behavior that I had not seen before. As low tide approached, a rocky, algae-covered substrate emerged around the dock, the usual resting place for 20–30 cormorants. I noticed that as low tide approached, cormorants would swim in very shallow water along the edges of the emergent substrate with their heads and bodies nearly submerged.
I decided to look at this foraging more closely because it superficially resembled the head-underwater, early phase of bathing that I had been observing. It soon became clear that the bathing and foraging were distinct. My notes read, “At 5:58 pm., a cormorant was in close to shore in shallow-water foraging, body and head nearly submerged, swimming along. Suddenly its head shot up, a fish wiggling in its bill. There was no doubt that it had been foraging.” Low tide that afternoon was at 3:59 pm.
The following day, low tide was at 4:51 pm, and I was out on the porch watching the cormorants. At 4:28 pm, I noticed a cormorant shallow-water foraging with its head and body nearly submerged and swimming along near the tide-exposed substrate to the right of the dock. When it swam to deeper water, it dove and disappeared from sight while foraging, the normal foraging behavior for cormorants (Dorr et al. 2020). At 4:42 pm, another cormorant foraged in shallow water with its head and body mostly submerged, bringing its head up about every five seconds (Figure 1). Another cormorant did the shallow-water foraging routine, raising its head every five to seven seconds as it swam along. This bird made an apparent foraging strike but came up, it appeared, with a piece of algae. The water was still and the wind was nearly nonexistent. At 4:52 pm, two more cormorants shallow-water foraged, raising their heads every five to seven seconds. At 5:08 pm, a sixth cormorant did the shallow-water foraging routine. On April 10, I was able to photograph two shallow-water foraging cormorants to the right of the dock (Figure 2).
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Figure 2. Two cormorants forage in shallow water with heads mostly submerged.
Structural features of the cormorant eye suggest that cormorants can see with precision underwater, a condition helped by a thick and flattened cornea and well-developed muscles within the eye (Dorr et al. 2020, Sivak et al. 1977). This explains why it is possible for cormorants to forage in shallow water with their heads submerged or nearly submerged. The Double-crested Cormorant account in Birds of the World (Dorr et al. 2020) makes no mention of the shallow-water foraging behavior I watched, although they do report, “Swimming cormorants occasionally hold their heads under water before diving, apparently looking for prey.” What I witnessed was a common and persistent behavior in shallow water that did not require diving.
Literature Cited
- Dorr, B. S., J. J. Hatch, and D. V. Weseloh. 2020. Double-crested Cormorant (Phalacrocorax auritus), Version 1.0. In Birds of the World (A. F. Poole, Editor). Cornell Lab of Ornithology, Ithaca, NY, USA. https://doi.org/10.2173/bow.doccor.01
- Sivak, J. G., J. L. Lincer, and W. Bobier. 1977. Amphibious visual optics of the eyes of Double-crested Cormorants (Phalocrocorax auritus) and the Brown Pelican (Pelecanus occidentalis), Canadian Journal of Zoology 55 (5):782–788.