02
Nov
November’s PolliNATION Pollinator of the Month: The Baltimore Oriole
(Beyond Pesticides, November 2, 2017) The Baltimore oriole (Icterus galbula) is Maryland’s state bird and the namesake of its professional baseball team. The Baltimore oriole (and all American orioles) are actually members of the blackbird family, and are related to the tricolored blackbird. For a time, the Baltimore oriole was “lumped” together with the Bullock’s oriole to the west under the name “northern oriole.” The “splitters” have won out again, and the two are recognized as separate species, except in the Western prairies, where they hybridize. In fact, the Baltimore oriole shows more genetic similarities to the Altamira oriole (which lives in Mexico, northern Central America, and a tiny part of Texas), and especially to the black-backed oriole (from Mexico).
Fun fact: The Baltimore orioles’ slender beaks allow them to feed in an unusual way. By first piercing soft fruits with their closed bills, the birds open their mouths to cut a strip through the juicy fruit, allowing them to drink the gushing liquid with their brushy-tipped tongues, in a process called “gaping.”
Range
Baltimore orioles are commonly found during spring and summer months in the eastern and central U.S., and in southern Canada. They will migrate in July to warmer habitats in southern U.S. states and Mexico, as well as in South America, where they will winter in open-forest habitat on shade-grown coffee and cacao plantations. Baltimore orioles avoid the dry season, returning to the Northern hemisphere when food and water in southern climes become scarce. The Audubon Society predicts that climate change will move the oriole’s nesting range further north over the coming century, eventually driving it out of Baltimore.
Physiology
The male has brilliant orange plumage with black and white wings. His tail is also black, with orange, flaring edges. He has a sharp-pointed silver-black bill, and a black head and upper back. The female’s bill is also pointed. Her colors, however, are somewhat subdued —her head and back are gray-olive, her breast and tail a lighter yellow-orange, and her wings gray-brown with white accents. Both males and females are medium-sized and have three toes pointing forward and one pointing back, a branch grip that enables the birds to perch. Both male and female sing — a song the Cornell Lab of Ornithology describes as “flute-like,” and “[consisting] of a short series of paired notes, repeated 2–7 times, lasting 1–2 seconds.”
Baltimore orioles are known for their distinctive hanging, pouch-shaped nests, typically anchored in drooping branches of tall shade trees such as the American Elm. Females take one week to build their nests out of flexible materials ranging from Spanish moss and twigs to fishing line and horsehair. Adults lay one clutch of 3–7 eggs per season. In summer, after breeding and before migrating, Baltimore orioles will molt their plumage. The diet of Baltimore oriole adults, while breeding and feeding their young, consists mostly of nutrient-rich insects, but they also consume sugar-rich fruits to store energy prior to and during their long migration.
Ecological Role and Threats to Existence
During the breeding season, Baltimore orioles eat a wide variety of insects, including many so-called “pest” species, such as larvae within plant galls, tent caterpillars, gypsy moth caterpillars, fall webworms, and spiny elm caterpillars, that many other bird species avoid. By foraging through the treetops, leaves, and branches, and feeding on large quantities of larvae and insects, the Baltimore oriole protects trees from suffering extensive damage.
During northern winter months, Baltimore orioles feed on fruit trees and vines in the Neotropics. While enjoying the fruit, many birds may ingest and excrete whole seeds, a symbiosis that feeds the bird while aiding the dispersal of the seeds through the oriole’s flight.
In visiting flowering trees and vines in search of nectar, Baltimore orioles become much-needed pollinators. In the process of reaching for nectar, having a comparatively shorter beak than the hummingbird’s, a Baltimore oriole’s body becomes covered with pollen, dusting the forehead, chin, bill, and feathery breast. As birds move from plant to plant, they carry pollen to nearby and adjoining flowers, pollinating plants wherever they feed.
A Baltimore oriole’s preferred plants have tight clusters of fruit and flowers, as well as sturdy supporting branches to enable a secure perch while feeding. Like the liana Combretum fruticosum of Mexico and South America, plants that attract Baltimore orioles and other strictly perching, or “passerine,” birds, produce very hexose-dominant (low in sucrose) nectars, which makes them poor hummingbird food.
Habitat loss at breeding and wintering grounds, pesticide use on neighboring farm fields and gardens, and collisions with glass are the principal threats to this species. In addition, in the mid-twentieth century, Dutch elm disease infected and killed a majority of American elm trees — favorite nesting trees for Baltimore orioles because of their spreading form and drooping branches.
How to Protect the Species
To deter collisions with frenzied flyers, put startling images or light-reflecting stickers on windows to make the surface more visible. See the American Bird Conservancy’s suggestions.
Protect existing wild spaces and large shade trees. As Baltimore orioles breed in open forest edges and riparian areas, on farms, and in fruit orchards, plant trees and native hedgerows along rivers and lakes. Water saplings regularly, apply mulch before harsher winter months, and monitor the health of maturing trees in your community.
Avoid using pesticides! Many toxic chemicals applied on lawns, farms, and sports fields are toxic not only to birds, but also, to insects. Pesticide spray can similarly poison Baltimore orioles’ much-loved fruit trees.
Backyard feeders are a great way to attract and sustain Baltimore orioles under stress, or during their preparation for southern migration to over-winter. Given orioles’ fondness for fruit and nectar, as well as insects, those interested in creating Baltimore oriole feeders in their backyard or school playground can incorporate orange slices, or even jam as a sugary nectar alternative. Baltimore orioles are especially attracted to dark-colored mulberries, cherries, and grapes.
Contact the American Bird Conservancy for further information.
Citations:
American Bird Conservancy, Baltimore Oriole: https://abcbirds.org/bird/baltimore-oriole/
The Cornell Lab of Ornithology: http://www.birds.cornell.edu/Page.aspx?pid=1478#_ga=2.11276977.429557172.1509474379-1750545177.1508945470
Avian Pollination: ftp://169.158.189.34/pub/Biotropica/1990s/1990/22-3/Biotropica-1990-22-3-p266.pdf
All About Birds, Baltimore Oriole: https://www.allaboutbirds.org/guide/Baltimore_Oriole/lifehistory
All About Birds, Baltimore Oriole, Bullock’s Oriole: https://www.allaboutbirds.org/guide/spp_photos.aspx?spp=3&sppid=36&keepThis=true&TB_iframe=true&height=488&width=875
Journey North, Oriole, “From Northern Oriole to Baltimore and Bullock’s
A Split Decision”: http://www.learner.org/jnorth/tm/oriole/Baltimore-BullocksSplit_Rising.html
Audubon Guide to North American Birds, Baltimore Oriole: http://www.audubon.org/field-guide/bird/baltimore-oriole
