What's in Flight

September 2018

‘It’s all about sex and food,’ says Paul Sweet, Collection Manager of the Ornithology Department at the American Museum of Natural History explaining the reason behind the annual bird migration, which is at its peak right now. The estimate is that more than triple the numbers of birds that fly north through the city in the spring are now returning south.  ‘For every two that come up, there are now six going back,’ says Paul Sweet, explaining that the explosion in numbers is due to all the chicks. ‘But it is a very perilous return journey.  A lot of them will not make it.’   

Blackburnian Warbler

Richard Phillip Nelson

All summer long the city has hosted many species of tropical birds.  But most migrants don’t stay here for more than a couple of days. They are just passing through. In the spring, most travel up to the northernmost parts of America, the boreal forests in Canada and even Alaska.  They fly North from places like the Caribbean, Mexico and South America. According to Paul Sweet, these birds are following the explosion of bugs and berries. ‘It’s not that they don’t have these food sources back home. it’s just they are more abundant further north and there’s less competition.’   In the spring, these tropical birds need a lot of energy for procreation.  The males especially, put on a tremendous show. They grow fancy colored feathers, they sing special songs to mark out their territory (and possibly attract a mate), and they need to build a nest, feed young and fly north.

Canada Warbler

Richard Phillip Nelson

By summer’s end, the performance is over and the tropical birds are conserving their energy and fattening up for the long journey home. For the Blackpoll Warbler, who sometimes summers as high up as Alaska and winters in Brazil, the round-trip is an epic journey of over 14,000 miles.  The Cornell Lab of Ornithology estimates that over 4 billion birds are flying south now along the four main bird highways that traverse America, including the Atlantic flyway that passes right over New York. 

Blackpoll Warbler 

Barrie Raik

Best days to spot tropical bird migrants in our park are when there is a Northeasterly wind, says Paul Sweet. It brings them down from the northerly climes. Paul’s other tips for bird watching are to stand still and listen, and to look for movement especially in the uppermost branches of the trees and around shrubs and trees with abundant berries. At this time of year, the warblers voices are different.  Most give a simpler ‘chip-chip’ call and not the more complex songs of spring. Also the bird’s plumage maybe less striking.  The males are more subdued and have lost some details. One of the most remarkable transformations is the male Scarlet Tanager, which is glowing red in spring and which molts to a greenish-yellow in the fall.

Scarlet Tanager male (spring plumage)

Barrie Raik

Scarlet Tanager male (fall plumage)

Joseph Baider for exploringbirds.com

One exciting and brightly colored visitor to the park this time of year is the Ruby-throated Hummingbird. Look for a flash of iridescent green as this tiny creature zips around feasting on all the low lying orangey-red tubular flowers, in particular Jewelweed, Trumpet Vines and Red Salvia. This tiny bird (only the male has a ruby red throat) weighs on average 0.13 oz. It is a delight to watch as it hovers in mid air sipping nectar with its needle-like beak. A hummingbird’s  blade-like wings can rotate 180 degrees and beat 55 times per second. This increases when the males are courting to a mindboggling 200 beats per second (a Guinness World Record for fastest wing speed). To fuel all this activity, hummingbirds have a very high metabolism, says Paul Sweet and hence they need to feed constantly. By the end of October, these shimmering metallic green birds will be back in their homelands in Florida, Mexico and Central America. 

Ruby Throated Hummingbird close up

Terry Collins

Ruby Throated Hummingbird

Joseph Baider for exploringbirds.com

Words: Lucie Young

Images: Joseph Baider for exploringbirds.com, Richard Phillip Nelson, Barrie Raik and Terry Collins

Link: American Natural History Museum Ornithology Department http://research.amnh.org/vz/ornithology/index.php

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