Do male Ruby-throated Hummingbirds migrate south before the females?

The Ruby-throated Hummingbird (Archilochus colubris) is the most common and widespread hummingbird species found east of the Mississippi River in North America. As their name suggests, male Ruby-throats have a brilliant ruby red throat, while females lack this distinctive coloration. Like many migratory bird species, Ruby-throated Hummingbirds undertake a remarkable biannual migration, traveling between their breeding grounds in the United States and southern Canada to their overwintering grounds in Mexico, Central America, and the Caribbean.

Migration Overview

Ruby-throated Hummingbirds have one of the most extensive migration routes of any hummingbird species. Their annual migrations exceed 3,000 miles roundtrip. Some key facts about their migration patterns include:

• They breed across eastern North America during the spring and summer, nesting as far north as central Ontario and southern Quebec in Canada.
• By early September, most Ruby-throats begin moving south towards their wintering grounds, with peak migration in late September.
• Their primary overwintering range extends from southern Mexico across Central America to Panama.
• The birds arrive on their tropical wintering grounds between September and late October.
• They remain in the tropics for 5-6 months before beginning the northward return migration in late March.
• By early May, the first Ruby-throats start arriving back on the U.S. Gulf Coast, reaching their most northern breeding areas by early June.

Tracking studies using tiny geolocators attached to wild Ruby-throats have helped map out their full migratory cycle and reveal their incredible endurance flights traveling over the Gulf of Mexico.

Do Males Migrate Before Females?

When it comes to the fall migration period, male Ruby-throated Hummingbirds generally begin moving south before females. However, there is some overlap between the sexes. Here is an overview of their migration timing:

• Adult males usually begin migrating south by early to mid-August.
• Immature males follow behind the adults, starting migration in late August.
• Females and juveniles mostly migrate in September and early October.
• Adult male numbers decline sharply on the breeding grounds by late August, but some females remain into early September.
• By late September to early October, most birds have migrated from their northern breeding areas.

Analysis of banding and observational data indicates males precede females by about two weeks on average during fall migration. However, as mentioned, there is considerable overlap between the sexes. It’s not an absolute division of earlier migrating males and later migrating females.

Why Do Males Migrate Earlier?

Researchers propose several key reasons why male Ruby-throated Hummingbirds generally migrate earlier than females in the fall:

1. Earlier arrival at wintering grounds to claim territories – By arriving first, males can secure the best overwintering territories which will give them an advantage in early spring when they return to the breeding grounds.
2. Molting priorities – Males undergo molt before migration to regrow worn breeding plumage. Females delay molt until they reach the wintering grounds.
3. Lower energy reserves – Males may need to migrate earlier because they carry less fat reserves than females at the end of breeding.
4. Competition avoidance – Leaving before wintering grounds become crowded with migrants may improve migration success.

Research suggests the males’ earlier departure provides an advantage in securing high-quality winter territories. This may ultimately help them arrive sooner at the breeding grounds in spring, where being early has reproductive benefits.

Do Females Follow the Same Migration Route?

In the fall, female Ruby-throated Hummingbirds follow the same southeast migration pathways and wintering destinations taken by males. Key research findings indicate:

• Banding data shows males and females overwintering together across the same geographic range.
• Tracking studies reveal females are equally capable of making long nonstop flights over the Gulf of Mexico.
• Females appear drawn to the same tropical habitats preferred by males.

The similarity in migration routes and wintering grounds supports the conclusion that females are following the same migratory path paved by males. They likely rely on genetic programming and social cues to guide them along the same flyways.

Spring Migration Patterns

The northward spring migration follows a different pattern in timing between the sexes. Here are the key details:

• In spring, females generally migrate first, initiating travel by early March.
• Males follow about one to two weeks behind females on the return trip.
• Females arrive back at the breeding grounds first, mainly during late April through early May.
• Males return mostly in May, reaching the northern limits by early June.
• In spring, the sexes follow the same flyways in reverse taken during the fall.

The females’ earlier spring departure may help them secure the best nesting sites and resources upon arrival. This early arrival is crucial because females alone build the nests and care for the young.

Sex Differentiation in Migration Timing

In summary, Ruby-throated Hummingbirds follow these general trends in migration timing between the sexes:

However, keep in mind there is considerable overlap between the sexes. The differences are a matter of weeks rather than a rigid schedule. Both sexes follow the same migratory flyways between the breeding and wintering grounds.

Why Is Migration Timing Important?

The timing of Ruby-throated Hummingbird migration has important consequences both during migration and on the wintering and breeding grounds:

• Early arrival at wintering areas allows males to claim prime territories.
• Early return to breeding grounds gives females first access to resources.
• Males may need to fuel up sooner for the long southbound migration.
• Females need extra time to prepare nests in the north.
• Staggered migration prevents overcrowding along migration routes.
• Different timing reduces competition between the sexes.

Ruby-throats are a fascinating example of how migration strategies differ subtly between sexes to maximize reproductive success and survival. Their amazing marathon migrations and sexual variations in timing reflect the pressures of their challenging lifestyle.

Conclusion

In conclusion, male Ruby-throated Hummingbirds begin their fall migration south about two weeks earlier on average than females. However, there is considerable overlap between the sexes during the migration period from August through early October as they travel from their breeding range to wintering grounds in Mexico, Central America, and the Caribbean. Males likely migrate first in fall to secure prime tropical territories and replenish energy reserves faster after breeding. In spring, females precede the males on the return trip north by one to two weeks. Their early arrival at the breeding sites gives females more time to build nests and establish breeding territories. Understanding migration patterns and timing provides insights into the behavioral adaptations that allow Ruby-throated Hummingbirds to complete their incredible biannual odyssey across the western hemisphere.