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Magnificent Frigatebirds – Determining Age and Sex

Alex Lamoreaux|

The Magnificent Frigatebird is one of the most well-known seabirds throughout the American tropics. Most recognize this species for the inflatable red gular sac shown on adult males but their remarkably long wings, forked tail, and piratical lifestyle make this species an incredible sight no matter what age or sex. In fact, frigatebirds have the longest wings compared to body weight of any species of bird!

I was fortunate to spend a few hours at Fort Jefferson in the Dry Tortugas National Park back in early March, where the local breeding population of frigatebirds is quite cooperative for photography. The Dry Tortugas is home to the only breeding location for this species in the United States, although they breed throughout the Caribbean and Central and South America. Prior to this visit, the closest I had ever been to this species was while driving down Route 1 through the Florida Keys and having an occasional flyover, but never had I seen them as close as they are at Fort Jefferson – sometimes flying so low over the island that I had trouble fitting the entire bird within my camera frame!

A molting adult male and an adult female Magnificent Frigatebirds gliding over the Dry Tortugas NP. (Photo by Alex Lamoreaux)

A molting adult male and adult female Magnificent Frigatebirds gliding over the Dry Tortugas NP. (Photo by Alex Lamoreaux)

Frigatebirds are actually the only family of seabirds who have fairly obvious plumage differences between male and female, as well as having a distinct immature plumage. The adult male Magnificent Frigatebird is glossy-black on both its upperside and underside, with a hint of purple and green on its back. During the breeding season, the adult male’s gular sac is bright red in color and is quite noticeable, even when not inflated. During the non-breeding season the male’s gular sac is an orange or yellow color.

The adult male Magnificent Frigatebird is glossy-black. This breeding male shows a red gular sac, which turns orange or yellow during the non-breeding season. (Photo by Alex Lamoreaux)

The adult male Magnificent Frigatebird is primarily glossy-black in color. This breeding male shows a red gular sac, which turns orange or yellow during the non-breeding season. (Photo by Alex Lamoreaux)

This upperside photo shows the adult male's glossy-black coloration, with a hint of green and purple throughout its back and upperwings. (Photo by Alex Lamoreaux)

This upperside photo shows the adult male’s glossy-black coloration, with a hint of green and purple throughout its back and upperwings. (Photo by Alex Lamoreaux)

The adult female is similar to the adult male, but has a white breast and black belly. Females and immatures, of course, lack a gular sac. Immature frigatebirds remain in their juvenile plumage for 4 to 6 years and then molt into their respective adult plumage type. The immature frigatebird is similar to the adult female, but the white on their undersides extends to their belly. Immatures also have a white head and shown a brownish tinge to their upperwings.

This adult female Magnificent Frigatebird shows a white breast, black belly, and black head. (Photo by Alex Lamoreaux)

This adult female Magnificent Frigatebird shows a white breast, black belly, and black head.        (Photo by Alex Lamoreaux)

Another view of an adult female Magnificent Frigatebird. (Photo by Alex Lamoreaux)

Another view of an adult female Magnificent Frigatebird. (Photo by Alex Lamoreaux)

Immature Magnificent Frigatebirds, like this one, are similar to adult females but have a white head and more extensive white on their undersides. (Photo by Alex Lamoreaux)

Immature Magnificent Frigatebirds, like this one, are similar to adult females but have a white head and more extensive white on their undersides. (Photo by Alex Lamoreaux)

Despite being a seabird, the frigatebird does not have a protective waterproof coating on its feathers, and so cannot actually dive to catch fish for itself. Instead, the frigatebird either plucks prey from the surface of the water with its long bill or takes on a more aggressive approach at securing a meal. The Magnificent Frigatebird is kleptoparasitic, meaning that it is very willing and able to chase down and steal food from other seabirds such as terns, gulls, and tropicbirds. The frigates will ruthlessly terrorize another bird for its food until the smaller bird either drops or regurgitates its meal, allowing the frigatebird to snatch the food out of the air. I don’t know about you but if I were something like a Royal Tern with a recently-caught fish and saw a group of frigatebirds coming towards me, like in the photo below, I would probably throw up too.

Three adult male Magnificent Frigatebirds up to no good. (Photo by Alex Lamoreaux)

Three adult male Magnificent Frigatebirds up to no good. (Photo by Alex Lamoreaux)

About the Author

Alex Lamoreaux

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Alex Lamoreaux has been an avid birder and naturalist since he was a youngster, growing up exploring the farmland and Appalachian ridges near Hershey, Pennsylvania. He attended Penn State University, studying wildlife biology. Alex has traveled extensively throughout North America, Central America, and South Africa and is a freelance nature tour guide, field biologist, and wildlife photographer. Alex has worked on wildlife research projects ranging from Whimbrel migration along the coast of Virginia to Yellow-billed Cuckoo nesting in the desert southwest. He has been the migration counter at the Hawk Ridge Bird Observatory for the past two fall seasons, documenting the massive visible migration of raptors and songbirds along Lake Superior. Alex loves to share his knowledge of nature, and strives to bring the birding community together to share in the fun that studying birds and wildlife has to offer. He has helped to organize and coordinate birding events in his home state of Pennsylvania and beyond. Contact Info Alex Lamoreaux aslamoreaux@gmail.com (717) 943-7086