American dippers are a type of songbird found across North America near swift moving streams and rivers. They are medium-sized birds with short tails and large heads. One of their most distinctive behaviors is constantly bobbing or dipping up and down along the water’s edge. This dipping motion serves several important functions for the birds.
Foraging
The main reason American dippers dip is to forage for food in the water. Their diet consists primarily of aquatic invertebrates like larval mayflies, stoneflies, caddisflies, and aquatic snails. The birds will walk along the shore or wade into the shallow water then dip their heads down to search for prey items hiding below the water’s surface. The dipping motion helps stir up sediments which reveals more potential food sources. It also allows the birds to use their tactile sense of touch to feel for prey along the streambed.
Dippers have special adaptations that allow them to dive and forage in swift streams. Their nostrils have valve-like flaps that close when they submerge so they can keep water out. They also have dense plumage that sheds water easily and helps insulate them from the cold water. Their wings are short and suited for swimming and maneuvering underwater rather than flying. Their legs are set far back on their bodies which gives them more power and leverage for diving.
By constantly dipping up and down in the water, dippers are able to thoroughly search a section of stream for any available insects or aquatic invertebrates. This movements allow them to find food even in dark or murky waters. Dipping also helps stir up prey items so they are more visible and easier for the birds to snap up.
Common dipper foraging prey items:
- Mayfly nymphs
- Stonefly nymphs
- Caddisfly larvae
- Aquatic snails
- Small fish
- Tadpoles
- Dragonfly nymphs
Visual Hunting
In addition to feeling for prey, dippers also use dipping to help them visually hunt for food. As they dip their heads under water, the birds are looking for signs of movement that reveal potential prey. The dipping action provides them with a constantly shifting perspective which makes small prey movements easier to spot. By repeatedly dipping in the same area, they are essentially scanning the streambed and visually surveying it from multiple angles in search of food.
American dippers have relatively large, well-developed eyes compared to other songbirds. Their pupils are able to dilate significantly to allow for greater light intake. This helps them see well enough underwater to hunt. The dipping behavior brings their eyes closer to prey so they can get a sharp, close-up view. Dippers will often focus their foraging on areas where the flowing water has the most riffles. This is where aquatic insects tend to accumulate and are washed along by the current. The dipping allows the birds to carefully watch these drift lines for any prey being carried by.
Communication
The dipping behavior of American dippers also serves as a form of communication. Mated pairs will often dip synchronously as a type of courtship ritual. The male and female mirror each other’s dipping motions which helps strengthen their pair bond. Males will also dip vigorously when defending their territory from intruders or proclaiming ownership of a section of stream.
Parents use dipping to communicate with their young. When feeding nestlings, the parents approach the nest with food visible in their bills. They will dip and bob around the nest entrance to signal to the chicks that they have arrived with food. This stimulates the nestlings to beg and flap their wings vigorously in response. Both adults and young dippers may also dip their heads low in a slow, exaggerated manner as a sign of submission or non-aggression to other birds.
Dislodging Prey
Another function of dipping is to help American dippers flush out prey hiding deep within rocky crevices. The birds will repeatedly dip their heads into cracks and crevices to try and drive out any invertebrates seeking shelter there. The dipping motion creates waves and turbulence that can knock small invertebrates loose. Dippers may also use their bills to tap along crevices to create vibrations that startle potential prey out of hiding.
Certain aquatic invertebrates like caddisfly larvae build cases made of small rocks, sand, or woody debris that they live inside for protection. Dippers will vigorously dip into these cases to knock the larvae loose so they can grab them up in their bills. The constant dipping motion allows them to deliver targeted mechanical forces to dislodge stubborn prey.
Searching for Nest Sites
During breeding season, male American dippers survey streamsides for suitable nesting sites by dipping methodically along the banks. They dip their heads into cavities beneath overhanging rocks, within logjams, or under the exposed roots of streamside trees. This dipping behavior allows them to inspect potential nest sites up close. When a suitable cavity is found, the male begins building a nest there by dipping his body down to carry moss, grass, leaves, and other materials inside.
Female dippers will also dip around prospective nests sites, often appearing to nonchalantly feed while surreptitiously checking out a nest under construction. They may alter nest materials by dipping into the nest to rearrange things more to their liking. So the dipping motion allows dippers of both sexes to thoroughly search out and evaluate possible nest locations.
Bathing
American dippers frequently dip their bodies into water to bathe and preen their feathers. Bathing helps dippers waterproof and maintain their plumage. By dipping repeatedly into the water, they are able to splash water over all of their body feathers ensuring they get fully soaked. The water washes away any accumulated oils or debris and helps realign feather barbules to seal the feathers.
Dippers will often bath more vigorously in the morning after spending the night roosting. This helps restore their plumage to prime condition for insulation and water resistance. Bathing may also help dippers dislodge any parasites like feather mites. The stream water contains Trace minerals that can be spread throughout the feathers as the birds preen after bathing. This may replenish minerals depleted through feather growth.
Interesting dipper bathing behavior:
- They prefer bathing in running water which is more invigorating.
- Often bathe by fluttering their wings in shallow water against the stream bed.
- Will dip bath communally, sometimes joined by other species like wrens.
- Young dippers begin bathing and preening almost immediately after leaving the nest.
Drinking
Dipping into the stream provides American dippers with drinking water. While dipping to forage, they will periodically swallow some of the water. They also deliberately take drinks by dipping down and tilting their heads back to swallow larger gulps of water. Drinking helps replenish the fluids they lose from their energetically active lifestyle.
Dippers tend to drink most frequently just after bathing. Bathing causes them to lose water from their feathers and skin that needs to be replaced. The fresh water may also help clear their nasal passages of any bathing debris or parasites flushed from their feathers. Periodic drinking gives dippers a source of fresh water to stay hydrated throughout the day between their bathing sessions.
Why Do They Dip So Frequently?
American dippers dip their heads into the water on average about 40 times per minute. This frequent dipping behavior occurs for several key reasons:
Hyperactive Metabolism
Dippers have very fast metabolic rates to support their active lifestyles. Their heartbeat is approximately 250 beats per minute while foraging compared to around 250-500 beats per minute while resting. To power this metabolism, they need to consume approximately 1/2 to 3/4 of their body weight in prey daily. The constant dipping provides frequent opportunities to find food to meet these needs.
High Energy Requirements
Living in and around frigid, fast-moving streams in cold climates requires a lot of energy for American dippers. The cold increases their heat loss while the rushing water provides resistance during swimming and foraging. The dippers maintain body temperatures around 104°F (40°C) even while immersed in 34-60°F water. Generating this heat requires continually stoking their metabolic fires with food energy attained through dipping.
Opportunistic Foraging
As aquatic insect populations rise and fall, dippers need to capitalize on any abundant food resources when available. Frequent dipping allows them to continuously sample the water for influxes of vulnerable prey. This opportunistic foraging helps ensure they get their fill during temporary population booms of different prey items.
Foraging Versatility
Different invertebrates become available during different seasons and life stages. Mayfly nymphs predominate in early spring while stoneflies, caddisflies, and dragonflies peak in summer and fall. Dipper’s constant dipping allows them to shift effortlessly between food sources. Their flexibility helps maintain adequate nutrition year-round as different aquatic insects wax and wane.
Limited Daylight Hours
American dippers are most active during daylight hours and rest at night. In winter at higher latitudes, they may only have 7-9 hours of daylight for foraging. Maximizing their food intake requires making the most of limited daylight. The continuous dipping and active foraging provides their best chance at consuming enough calories in the truncated winter days.
Minimal Caching of Food
American dippers do not cache or store appreciable food reserves. Other birds stash food like seeds, nuts, or fruit to eat later, but dipper’s aquatic insect diet does not keep well. Their foraging strategy relies on immediate consumption of prey. Frequent dipping provides a steady stream of food intake necessary in the absence of caching.
Limited Territory Size
Dippers defend linear territories along streams that are only about 250-450 feet long. Their territories provide a limited area to forage. Frequent dipping within this restricted space allows them to thoroughly exploit their territory without needing to expand along more of the watercourse.
High Energy Needs of Young
American dipper chicks grow very rapidly, nearly doubling their hatching weight in just 5 days. They beg incessantly for food with piercing calls and constant wing flapping. The adults make hundreds of foraging trips per day to satisfy the young. Their frequent dipping maximizes feeding rates to meet the considerable energy requirements of their fast-developing brood.
Additional Dipping Adaptations
Beyond the reasons why they dip so often, American dippers also have several physical and behavioral adaptations that facilitate their dipping lifestyle:
Flexible Necks
Dippers have more cervical vertebrae than most birds giving their necks greater flexibility. They can extend their necks further and pivot their heads more freely to reach into crevices. This flexible neck helps expand their dipping range of motion.
Water-shedding Plumage
The feather structure of dippers causes water to bead up and roll off the surface rather than penetrate the layer of trapped air beneath. Keeping their feathers waterproof allows for dry insulation after dipping.
Transparent Eyelids
American dippers have a third transparent eyelid called a nictitating membrane. This can cover their eyes underwater to protect their vision while still allowing them to see.
Slow Motion Dipping
When scanning for prey, dippers dip slowly and methodically. This gives their eyes time to thoroughly scan the stream bottom and detect signs of food.
Rapid Dipping
Once prey is spotted, dippers can make rapid, sustained dips to disturb hiding spots and flush out food items before they disappear.
Shallow Dipping
Along shallow margins dippers merely dip their bills and head underwater. This allows them to snap up larvae and insects without fully submerging.
Deep Dipping
In deeper areas, dippers will dip their entire body underwater. Having short wings and dense plumage facilitates diving.
Perch Dipping
Dippers often perch on streamside rocks and dip from an anchored position. Perching provides stability in heavy currents.
Wading Dipping
Wading through shallows allows dippers to stir up the streambed and flush out more prey in the turbid water.
Swimming Dipping
Strong swimming skills allow dippers to dip and forage even in fast, deep stream channels.
Other Water-related Behaviors
In addition to dipping, American dippers display some other interesting water-associated behaviors and adaptations:
Stream Bathing
Instead of dust baths like some birds, dippers bathe by fluttering their wings rapidly while submerged in streams.
Streamlined Body Shape
Their compact shape and short tail reduces drag for swimming and diving.
Powerful Legs
Strong legs placed far back on their bodies provide propulsion for diving and walking underwater.
Grip Pads
Small bumps on their toes help grip slick, wet rocks. These allow them to climb over wet cascades and rapids.
Vocalizations
Their “dip” call sounds similar to their dipping motion and resonates well around water.
Aquatic Insect Diet
Feeds almost exclusively on stream invertebrates adapted to aquatic life.
Riverbank Nesting
They nest in cliff crevices, logjams, and roots along the watercourse.
Conclusion
In summary, American dippers are uniquely adapted to their specialized niche around cold, clear streams and rivers. Their distinctive dipping behavior serves critical functions related to foraging, communication, bathing, and drinking. Frequent dipping allows them to find adequate food and stay alert for threats or courtship opportunities. Due to their high metabolic needs and constrained territory space, dippers must dip often and opportunistically. Excellent adaptations like transparent eyelids, waterproof plumage, and flexible necks facilitate their constant dipping lifestyle. The American dipper’s intimate connection with moving water makes it a fascinating bird perfectly suited to its riverbank environment.