Many species of birds migrate at night to take advantage of cooler temperatures, calmer winds, and fewer predators. Nocturnal migration allows birds to feed and rest during the day and cover more distance when the skies are clear at night. Some of the most common birds that migrate at night include warblers, thrushes, sparrows, shorebirds, and waterfowl.
Why do some birds migrate at night?
There are several key advantages for birds that migrate at night:
- Cooler air temperatures at night help prevent overheating and dehydration during long flights.
- Calmer wind conditions provide a smoother flight with less turbulence.
- Fewer predators like hawks and eagles are active to hunt migrating birds at night.
- Daytime hours allow birds to rest and refuel for the next night’s migration.
- Clear skies and the moon/stars can help guide navigation on migration routes.
Many daytime predators like raptors are visual hunters, so migrating under the cover of darkness provides safety and conserves energy. Birds that migrate during daylight still stop to rest at night. Nocturnal migration allows birds to get the most mileage by flying all night and feeding all day.
How do birds navigate at night?
Birds utilize several techniques to navigate accurately during nighttime migration:
- moon and star navigation by sight – the moon especially can provide directional cues
- using an internal magnetic compass
- navigation by geographical landmarks
- detecting low-frequency sounds like ocean waves
- olfactory cues from smells like pine forests
Some migratory birds have the ability to sense the Earth’s magnetic fields, using them like a compass to determine their direction and orientation. Visual cues from celestial objects, as well as landmarks, scents, and sounds, provide additional guidance mechanisms. Many birds prepare for migration by studying details of the night sky to calibrate their internal compasses before embarking on long journeys.
What birds are nocturnal migrants?
Some of the most common species of birds that migrate at night include:
Warblers
- Northern Parula
- Magnolia Warbler
- Yellow Warbler
- Chestnut-sided Warbler
- Blackpoll Warbler
- American Redstart
- Black-throated Blue Warbler
Thrushes
- Swainson’s Thrush
- Hermit Thrush
- Veery
- Gray-cheeked Thrush
- Wood Thrush
Sparrows
- White-crowned Sparrow
- Lincoln’s Sparrow
- White-throated Sparrow
- Song Sparrow
Shorebirds
- Sanderling
- Semipalmated Sandpiper
- Western Sandpiper
- Dunlin
- Short-billed Dowitcher
- Solitary Sandpiper
Waterfowl
- Northern Pintail
- Green-winged Teal
- Blue-winged Teal
- Northern Shoveler
- Gadwall
- American Wigeon
- Canvasback
- Redhead
These species exemplify some of the diverse types of birds that undergo nocturnal migrations between their breeding and wintering grounds each year. The phenomenon spans entire groups like warblers, thrushes, shorebirds, and waterfowl that all share the adaptation for nighttime migrations.
Why do different birds migrate at night than day?
There are a few key reasons why some birds prefer to migrate at night while others migrate during the day:
- Smaller birds like warblers tend to migrate at night to avoid predators – their size makes them vulnerable.
- Diurnal raptors like hawks choose to migrate during the day when they can utilize thermals and updrafts to soar and conserve energy.
- Shorebirds migrating over water at night can utilize coastal landmarks, wave sounds, and star navigation as orientation cues.
- Waterfowl that feed in shallow wetlands during the day migrate at night to reach new feeding grounds by morning.
- Some younger birds may choose to migrate during daylight hours their first migration before switching to nocturnal patterns.
Habitat preferences, risk of predation, feeding behaviors, experience level, and intrinsic adaptations all contribute to whether a species is predisposed towards nocturnal or diurnal migration. The strategies all help different types of birds maximize safety and efficiency on their migratory journeys.
How do birds migrate long distances at night?
Birds have many physiological and behavioral adaptations that allow them to undertake incredibly long migrations strictly at night:
- Highly efficient flight techniques and aerodynamics that minimize energy expenditure.
- Ability to fuel up by hyperphagia, nearly doubling their body weight before migration.
- Endurance training before migration to improve stamina.
- In-flight fueling by snacking on insects and aquatic invertebrates.
- Flying in optimal high-altitude tailwinds when possible.
- Strong navigation abilities via moon, stars, geomagnetic cues etc.
- Making optimal stopover decisions to rest and refuel.
Many birds can migrate thousands of miles over oceans, deserts, and mountain ranges all while flying exclusively at night. Their physiology sustains them, their navigational skills guide them, and their stopover timing gives them the rest and food they need to complete their marathon migrations.
How fast and high do nocturnal migrant birds fly?
The flight speeds and altitudes of nocturnal migrant birds can vary significantly by species, weather conditions, and geography. Some general ranges include:
- Flight Speeds: 10 – 60 mph
- Flight Altitude: 1,000 – 10,000 ft
Small birds like warblers tend to migrate at slower speeds, usually ranging from 15-35 mph. Larger birds like shorebirds can fly up to 60 mph. Headwinds and tailwinds play a major role in groundspeed.
Most nocturnal migrants fly from 1,000 to 3,000 ft altitude. Some birds migrate as high as 10,000 ft on nights with ideal winds aloft. Lower altitudes are used in crossing mountains and along coasts.
Average Migration Speeds by Bird Group
Bird Group | Average Speed (mph) |
---|---|
Warblers | 15-25 |
Thrushes | 20-30 |
Shorebirds | 30-60 |
Waterfowl | 25-50 |
What weather conditions are best for night migration?
Birds migrate under a diverse range of weather conditions, but some factors make for more efficient and successful nocturnal migration:
- Cool, calm winds
- Tailwinds in direction of travel
- Clear skies or high cloud cover
- Waxing or full moon for visibility
- High pressure weather systems
- Absence of precipitation
Winds are one of the most important factors governing the intensity of migration on a given night. Calm winds allow for maximum progress, while headwinds cause more difficult flight. Low clouds make navigation tougher, while rain or snow can be deadly.
Ideal conditions see high numbers of migrants taking advantage of peak travel conditions. Inclement weather often results in lower migration densities as birds wait for better skies.
Migration Traffic Under Different Weather Conditions
Weather Factor | Migration Intensity |
---|---|
Tailwinds >15 mph | Heavy |
Calm winds | Moderate |
Headwinds >15 mph | Light |
Low clouds | Light |
Clear skies with moon | Heavy |
Precipitation | None to light |
Conclusion
Nocturnal migration allows many species of birds to maximize travel under optimal nighttime conditions. Warblers, thrushes, shorebirds, and waterfowl are all adept at navigating their migrations strictly at night. Cool temperatures, calm winds, clear skies, and geomagnetic guidance all facilitate these incredible journeys. Understanding nighttime migration gives us appreciation for the amazing distances birds travel between their breeding and wintering grounds twice each year.