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Least Tern Identification

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The Four Keys to ID

  • Size & Shape

    A distinctive, very small seabird, slim in all proportions, with long, narrow wings, trim body, and slender, sharp bill.

    Relative Size

    Larger than a Tree Swallow, smaller than a Forster's Tern.

    Relative Sizebetween robin and crowbetween robin and crow

    • Both Sexes
      • Length: 8.3-9.1 in (21-23 cm)
      • Weight: 1.3-1.9 oz (36-54 g)
      • Wingspan: 18.9-20.9 in (48-53 cm)

Regional Differences

Five very similar-looking subspecies have been described. The widespread antillarum breeds from Maine to Venezuela. California Least Tern (browni) breeds in California and Baja California. Interior Least Tern (athalassos) breeds in inland North America, primarily along the Mississippi River and its tributaries. Two less well-known subspecies, mexicana and staebleri, occur from the Gulf of California to Chiapas, Mexico.