The vendor who sold me this hashioki said that the bird was a seagull.
But it didn’t look like a seagull to me; the bird was too small and too plump. So I started looking for a different explanation.
This hashioki looked a lot like a Mt. Fuji chopstick rest that I had previously purchased online from Bento & Co., a wonderful store in Kyoto. When I checked their site I found that the hashioki were indeed related, and that they were made by a company called Kihara. When I visited the Kihara site I discovered the name of this pattern is nami (wave) chidori (plover).
The chidori, or plover, is a sparrow-sized bird that likes to wade in the surf or shallow river waters. They are migratory birds which spend the summer in Siberia, and the winter in Japan. They travel in flocks, which probably explains their Japanese name; the kanji for chi means one thousand, and the kanji pronounced dori means birds. Because chidori migrate great distances, flying over rough seas in heavy winds while they travel, they are considered a symbol of perseverance. For Japanese warriors they were an emblem of someone who would fight to overcome obstacles (1).
I think nami chidori would be a good emblem for hashioki collectors, too; identifying and researching require a fair amount of perseverance, too.
Nami chidori, the combination of plovers flying over waves, is a popular design motif in Japan. It is especially favored in summer because the image of a winter bird is thought to bring the suggestion of coolness to a hot day.
(1) Baird, Merrily. Symbols of Japan: Thematic Motifs in Art and Design. New York: Rizzoli International Publications, 2001, p. 103.