last week, this tweet went viral and a lot of people sent it to me, which is nice because i like when people think of me and also it is extremely relatable. i don’t know anything about the author or their knowledge of birds or if they picked the yellow-rumped warbler on purpose, but yellow-rumped warbler is actually an extremely good and relevant bird to notice, especially in nyc. all that is because of its relationship to a very common coastal plant, the northern bayberry.
i think one of the first lessons you learn as a birdwatcher is “if you wanna find birds, you have to find food.” as it turns out, new york city is fully-stocked with bird food all winter long—so much food that it harbors some surprising wintertime residents, despite the cold. northern bayberry is that food, and yellow-rumped warblers are those residents.
northern bayberry is a shrub which grows in sandy soil from the mid-atlantic to canada, encountered frequently along nyc’s coast. i’m pretty fond of it as a human, too, thanks to its thick green leaves which smell much like the bay leaves you’d put into stew (though the spice, bay laurel, is not related to bayberry). while i’m busy stuffing my fanny pack with nice smells, the birds are more interested in the bunches of waxy white berries.
the yellow-rumped warbler, affectionately known as the butterbutt (or yump), happens to be bayberry aficionado numero uno, and is therefore among the most common wintertime songbirds on the nyc coast thanks to these fragrant shrubs. warblers are typically a tropical, insect-eating bunch, spending all but the breeding and migratory seasons in central or south america before heading northward to raise a family on the glut of protein-rich insects in the northern forest each summer. yellow-rumps are also bug eaters in the summer and on migration, but not as much in the winter. according to birds of the world, the stomachs of butterbutts in coastal north carolina contained around 78% plant material, mostly bayberry. this adaptation allows them to winter where tropical birds can’t, as far north as nova scotia.
eastern yellow-rumped warblers are so tied to these plants that they were once called the myrtle warbler, from wax-myrtle, a plant closely related to the bayberry on which the warblers feed in the more southerly part of their wintering range.
it turns out that these birds are just built different, and have a special digestive tract that allows them to eat what other warblers can’t. for example, yellow-rumps can chew their cud like cows—they move food from their intestines back into their gizzard, the bird organ that replaces teeth for grinding food. they also have more salt in their bile to help break down the waxy berries. in exchange for these adaptations, they get the berries’ carbohydrates, fats, and proteins, which allow them to survive until bugs become more abundant in spring.
but yellow-rumps aren’t the only birds able to eat these berries. the tree swallow can survive on bayberry, too.
tree swallows are aerial insectivores; they specialize in fluttering around big open spaces to catch flying insects. but, while their relatives migrate deep into the tropics during the winter, tree swallows stay in the southeastern united states, and in some years, into new york city or even further north. last winter, birders were regularly reporting dozens to hundreds of tree swallows at breezy point in queens into february. these birds, too, are capable of digesting bayberries and will survive on bayberries when insects are scarce.
while new york’s sandy soil and salty air probably doesn’t sound appealing to your average plant, it’s perfect for bayberries, and therefore perfect for yellow-rumps and some tree swallows, too. and, i don’t know, maybe the urban heat island effect makes the city a slightly more appealing wintertime habitat. either way, it’s pretty neat to me that for so many birds, new york’s coast becomes a critical part of their wintertime survival thanks to this nice-smelling plant.
please keep sending me viral nature tweets. they make me happy and provide me with good newsletter fodder.
postscript:
people have actually been coming to my walks from the newsletter - it’s great and i hope to continue seeing some of you there! i have two more walks this week:
sept 30 - i’ll be at bryant park again at 5pm, at the entrance on 42/6. we saw a lot of surprising birds up close last week so i’m hoping this week will be just as good.
oct 2 - i’ll be in brooklyn’s prospect park leading a walk from 8am to 10am. it’s free, but requires sign-ups here.
this is the last walk i’ll be leading until november as far as i know, so i hope to see some of you there!
finally: i generally don’t recommend grabbing ahold of a bayberry-looking plant unless you’re sure that’s what it is, because poison ivy can look really similar when the leaves have fallen off. i’m preeeetty sure that the bayberry lookalike on which this ruby-crowned kinglet is feeding is poison ivy.
