Bullock’s Orioles are striking black and orange birds that breed in western North America and winter in Mexico. In the opening paragraphs, we’ll answer some key questions about where these birds spend the winter months.
Do Bullock’s Orioles migrate?
Yes, Bullock’s Orioles are migratory birds. They breed during the summer months in parts of western North America, then migrate south to overwinter in Mexico and Central America. The migration allows them to take advantage of abundant food resources during the breeding season, then escape harsh winters where food is scarce.
Where is the winter range of Bullock’s Orioles?
The winter range of Bullock’s Orioles spans Mexico and ranges into Guatemala, El Salvador, Honduras and Nicaragua. Their winter range centers on western Mexico, with highest densities along the Pacific coast.
Some key areas where Bullock’s Orioles overwinter include:
Southern Baja California
Bullock’s Orioles winter along both the Pacific and Gulf coasts of southern Baja California. Habitats used include palm oases, suburban areas, and agricultural fields.
Western Mexico
The western Mexican states of Sonora, Sinaloa, Nayarit, Jalisco, Colima, Michoacán, Guerrero and Oaxaca host wintering Bullock’s Orioles, mostly on the Pacific side. They frequent coastal scrub, agricultural areas, and groves of flowering trees.
Southern Mexico
Bullock’s Orioles occur as winter residents down into Chiapas, the southernmost state of Mexico. They are also found in interior Mexico in regions like the Balsas River valley where suitable habitat exists.
What habitats do Bullock’s Orioles use in winter?
Bullock’s Orioles use a variety of habitats during the winter months in Mexico and Central America. Some key habitat features include:
– Coastal scrub dominated by flowering plants like acacias.
– Groves of flowering trees like eucalyptus, palm, and kapok.
– Agricultural areas, especially those growing fruit crops.
– Riparian woodlands along waterways.
– Suburban parks and gardens with trees, flowering plants, and feeders.
Access to nectar and fruit bearing plants seems especially important to wintering Bullock’s Orioles. They also frequent areas with abundant insects like agricultural fields.
What fruits and flowers do wintering Bullock’s Orioles eat?
The diet of Bullock’s Orioles during winter consists largely of nectar and fruit. Some key food sources include:
Eucalyptus
Eucalyptus trees, native to Australia but planted widely in the winter range, provide an excellent source of nectar. The flowers also attract insects.
Kapok
Kapok trees produce abundant nectar from their large red flowers. Orioles often nest in kapok trees as well.
Acacia
Acacia flowers are rich in nectar. Insects attracted to the flowers also provide food.
Palms
Palms like date palms provide sugary nectar. Palm fruits are also eaten.
Ficus
Figs from Ficus trees offer a high-energy fruit food.
Citrus
Oranges, grapefruits and other citrus are readily taken.
Bananas
Banana plantations provide a convenient food source.
| Flowering Tree | Nectar | Fruit |
|---|---|---|
| Eucalyptus | X | |
| Kapok | X | |
| Acacia | X | |
| Palms | X | X |
| Ficus | X | |
| Citrus | X | |
| Bananas | X |
How do wintering habits vary between sexes and age classes?
There are some differences in the wintering ecology between male and female Bullock’s Orioles, as well as between younger and older birds:
Males vs Females
– Males tend to winter farther north than females on average.
– Males frequent more open, drier habitats like palm oases.
– Females are more likely found in denser, wetter habitats like riparian woodlands.
– Females seem more attracted to sugar sources while males target more protein-rich insects.
Younger vs Older birds
– Younger birds migrate later and arrive on the wintering grounds after adults.
– Juveniles frequent more semi-wild habitats like groves of flowering trees.
– Old adults are more likely to visit backyard feeders and urban areas.
– Adult males tend to be dominant over young birds at prime nectar sources.
When do Bullock’s Orioles arrive and depart from their winter grounds?
Arrival and departure times on the wintering grounds vary by location, age, and other factors:
Fall Migration
– Adults begin arriving in mid-September.
– Peak periods are late September to mid-October.
– Juveniles arrive in late October into November.
Spring Migration
– Early departures begin in February.
– Peak departure is late March to early April.
– Males, adults and more northerly breeders leave earliest.
– Stragglers may remain into mid-May.
– Most birds have departed the winter grounds by late April.
| Age/Sex | Fall Arrival | Spring Departure |
|---|---|---|
| Adult Males | Mid-Sept | Late March |
| Adult Females | Late Sept | Early April |
| Juveniles | Late Oct | Mid-April |
Conclusion
In summary, Bullock’s Orioles migrate from western North America to winter primarily in Mexico. Their winter range centers on coastal regions and agricultural areas with flowering trees that supply nectar and fruit. Microhabitats and food resources vary somewhat between age and sex classes. Birds arrive on the wintering grounds in fall starting in September, and depart for the north again in spring from February through April. Understanding details of their winter ecology helps explain population trends and conserve these beautiful migratory songbirds.
