Sandpipers are a family of small to medium-sized shorebirds that are found worldwide. There are around 30 different species of sandpipers, and they inhabit beaches, mudflats, rocky coasts, and the edges of bodies of water. Sandpipers have long legs and bills that allow them to wade in shallow water and probe for food. Some of the most common species of sandpipers include the spotted sandpiper, least sandpiper, dunlin, sanderling, and semipalmated sandpiper.
Sandpipers display an interesting mix of diurnal and nocturnal behaviors that varies between species. Some sandpipers are strictly diurnal, meaning they are active during the daytime. Other species exhibit crepuscular behaviors, meaning they are most active at dawn and dusk. And some sandpipers display facultatively nocturnal behaviors, meaning they are sometimes active at night depending on factors like weather, tides, food availability, and predation risk. Determining if a species of sandpiper is nocturnal depends on understanding its natural history and typical activity patterns in the wild.
In this article, we’ll take a close look at sandpiper natural history and research to understand if and when different species exhibit nocturnal behaviors. We’ll examine how factors like foraging ecology, predation risk, tide timing, and seasonal changes influence the propensity of sandpipers to be active at night. Read on to learn more about the nocturnal ecology of these widespread shorebirds.
Foraging Ecology
One of the main factors influencing sandpiper nocturnality is their foraging ecology. Most sandpipers have sensory adaptations like touch and sight that allow them to hunt visual prey during daylight hours. For example, the spotting patterns on their plumage help camouflage them against open shoreline habitats while stalking prey. And they have large eyes placed on the sides of their heads to give them excellent panoramic vision suited for spotting prey movement during the day.
But some sandpipers switch to hunting by touch at night. These tactile foragers, like the dunlin, use their bills to probe for buried prey in mud or sand flats. Nocturnal touch foraging doesn’t require as much visual acuity, so some sandpipers take advantage of the cooler nighttime temperatures when intertidal invertebrate prey may be more active. Other sandpipers that rely more on sight switch to foraging strategies like gleaning dead or dormant prey from substrate surfaces at night when live prey is scarce.
The availability of different prey types is another element influencing nocturnality in sandpipers. On many mudflats, the diversity and density of prey shifts between day and night as different invertebrates and fish emerge. Sandpipers may opportunistically forage whenever prey availability is highest, whether day or night. Migrating sandpipers stopping to refuel may also maximize foraging time by feeding both day and night when prey is abundant.
Predation Risk
Predation danger is a key reason why some sandpipers avoid nocturnal activity. Sandpipers that forage out in the open during the day are vulnerable to raptors and other diurnal predators. But venturing out on exposed tidal areas at night when visibility is low would likely increase their risk of predation. Instead, these shorebirds often roost in groups at night to lower individual risk. They may also seek sheltering habitats like dense vegetation that helps hide them from nocturnal predators.
Some sandpipers alter their nocturnal patterns based on moon phase to reduce predation danger. When moonlight illuminates the tidal zones, making nocturnal foraging safer, they are more likely to exhibit foraging activity at night. But on darker moonless nights, most sandpipers decrease or cease nocturnal activity to avoid becoming prey themselves.
Sandpipers on migration may also minimize nocturnal activity when stopping at unfamiliar sites along their migration route. With lack of knowledge about local conditions and potential dangers, avoiding unnecessary nocturnal foraging helps migrating sandpipers reduce their predation risk in unfamiliar surroundings. Instead they concentrate foraging during safer daylight hours when they can better detect potential threats.
Tidal Cycles
The ebb and flow of tidal cycles influence sandpiper behavior in coastal habitats. On tidal mudflats, retreating tides expose rich feeding areas during low tide that offer an abundance of accessible prey for sandpipers. High tides that flood these areas force sandpipers to roost or seek alternative foraging habitats.
Some sandpipers have adapted to take advantage of tides by exhibiting tidal rhythm chronotypes. This means their daily cycles of rest and activity align with regular tidal fluctuations. They rest during high tide when foraging areas are inundated and become active to forage during optimal low tide conditions.
Tide Stage | Sandpiper Behavior |
---|---|
High Tide | Resting |
Ebbing Tide | Foraging activity increases |
Low Tide | Peak foraging activity |
Flooding Tide | Foraging decreases |
In regions with large tidal fluctuations, low tides may occur both day and night. Sandpipers exhibit tidal rhythms by foraging intensely at low tide regardless of time of day. This adaptation allows them to take advantage of the best feeding opportunities when they occur. Some common sandpipers like dunlins routinely forage nocturnally to match low nighttime tides in certain habitats.
Some sandpipers will additionally forage during high tide if nighttime low tide conditions provide insufficient foraging time. Altering activity patterns relative to tidal fluctuations helps ensure sandpipers meet their daily energy needs within spatially and temporally variable coastal environments.
Seasonal Shifts
The time of year influences sandpiper nocturnality patterns as well. During spring and summer breeding seasons, most sandpipers are diurnal to maximize foraging time and provisioning rates for their offspring. But non-breeding sandpipers shift their activity patterns between seasons.
Some species that defend feeding territories during breeding season form large nocturnal foraging flocks in winter. More eyes watching for predators enables safer nocturnal foraging. And wintering sites that experience huge influxes of migrating sandpipers face intense competition for limited prey resources. Expanding foraging activity into the night relieves some of that pressure.
In warmer habitats, heat stress also influences sandpiper schedules. Nocturnal foraging allows sandpipers to avoid hot midday temperatures and accompanying higher evaporative water loss. Cooler temperatures, higher humidity, and lower solar radiation make nighttime activity more efficient and less physiologically taxing.
The following table summarizes how breeding season influences nocturnality in select sandpiper species:
Species | Breeding Season | Non-breeding Season |
---|---|---|
Dunlin | Diurnal activity | Nocturnal and diurnal activity |
Western sandpiper | Mostly diurnal | More nocturnal activity |
Spotted sandpiper | Cathemeral activity | Cathemeral activity |
Nocturnal Roosting Behavior
When not actively foraging, sandpipers exhibit communal roosting behavior that concentrates their resting activity during the night. Forming large roosting flocks provides safety in numbers through shared predator vigilance and predator confusion. And overnighting on open beaches, mudflats, and marshes near foraging sites allows quick access when tides change.
Some common roosting behaviors seen in sandpipers:
- Gathering in groups numbering from 10 to over 100,000 birds
- Selecting sites with wide visibility to detect approaching threats
- Flocking together tightly overnight
- Relying on peripheral birds to sound alarm calls if danger appears
- Roosting on ground at high tide; roosting up on rocks, jetties, or docks during low tide
Large roosting flocks often swirl and wheel in synchronized movement when taking flight, making it hard for predators to track any single bird. Periodic circling flight at night may also allow sandpipers to reorient themselves and stay aware of their surroundings.
Some small groups will roost solitarily, selecting more sheltered roost sites hidden in vegetation during times of high predation risk like migration. But communal roosting benefits most sandpipers overall through improved anti-predator responses and shared information exchange about local foraging sites.
Migration
Sandpipers that migrate long distances exhibit a mix of diurnal and nocturnal activity. Most migratory movement occurs at night when atmospheric conditions support longer flights. The cooler night air allows sandpipers to minimize overheating and dehydration during sustained physical exertion. Navigating is also easier under starry night skies.
But migrating sandpipers stop to rest and refuel during the day. High intake is needed to rebuild energy and fat stores for the next overnight migratory push. Sandpipers may also take advantage of daytime thermals and updrafts that provide additional lift to aid flights. The combination of alternating nighttime migratory flights with daytime refueling allows sandpipers to complete their biannual journeys over vast distances.
Influence of Artificial Lighting
Increasing light pollution from human development along coastlines can alter sandpiper nocturnal activity patterns. Bright lights that illuminate otherwise dark beaches and wetlands at night may offer improved visibility for sandpipers to visually forage. This allows more diurnal species to opportunistically expand their foraging into the nighttime hours in artificially lit areas.
But excessive artificial light also negatively impacts sandpipers. It can disrupt their natural circadian cycles adapted to darker nights. Bright night lighting leads to less resting time for sandpipers that need to remain vigilant against the increased risk of nocturnal predation. And migrating sandpipers can become disoriented by artificial light pollution, wasting energy and risking injury or death.
Overall, maintaining naturally dark coastal areas at night benefits sandpipers long-term. Targeted use of shielded, low intensity lighting where needed by humans can still allow sandpipers to behavior naturally and safely at night.
Conclusion
In summary, sandpiper behavior at night depends on a variety of intrinsic and environmental factors influencing the costs and benefits of nocturnal activity versus rest. Some species like the spotted sandpiper maintain cathemeral activity rhythms, alternating between periods of daytime and nighttime foraging as conditions dictate. Others specialize in being strongly diurnal or nocturnal depending on their habitat and ecology.
Most sandpipers exhibit greater nocturnal behaviors outside of breeding season when energy demands are reduced or competition for resources intensifies. Crepuscular routines around dawn and dusk transitions are also common among sandpipers. Overall, the flexibility in their diel rhythms allows sandpipers to take advantage of tidal, seasonal, and other environmental fluctuations they encounter within their coastal habitats worldwide. Careful observations of identified individuals is needed to fully understand a particular species’ nocturnal tendencies based on influencing factors.