The Eastern Whippoorwill (Antrostomus vociferus) is a medium-sized nocturnal bird found in eastern North America. Whippoorwills are part of the nightjar family (Caprimulgidae) and are named for their distinctive “whip-poor-will” call. They have large mouths for catching flying insects at night. Understanding the diet and foraging habits of whippoorwills can provide insights into their ecology and conservation needs.
Insects
Eastern Whippoorwills are insectivores, meaning insects make up the bulk of their diet. They capture insects on the wing, most often at dawn and dusk. Some key prey insects include:
- Moths
- Beetles
- Flies
- Mosquitoes
- Crickets
- Grasshoppers
- Cicadas
- Dragonflies
Moths in particular are an important food source. A study examining the stomach contents of whippoorwills in Missouri found that over 50% of prey items were moths from the families Noctuidae, Geometridae and Pyralidae. Other common prey included beetles (Coleoptera), true flies (Diptera), and true bugs (Hemiptera).
Whippoorwills hunt insects by perching and waiting, then making quick sallies and dives to capture prey on the wing. They often return to the same perch while hunting. Their large, gaping mouths allow them to scoop up insects during flight. They also sometimes glean insects from surfaces while hovering briefly.
Seasonal Variation
The diet of whippoorwills changes based on seasonal availability of different insect prey. In spring and summer, they take advantage of the seasonal boom in flying insects. Caterpillars that later metamorphose into moths and beetles are abundant at this time. As the season shifts to fall, dragonflies, grasshoppers, crickets, and cicadas become more prevalent in the diet.
One study in Oklahoma found that lepidopteran larvae (caterpillars) were the most common prey in May, making up around 30% of the diet. By July, the diet shifted to include more adult moths and beetles. In August-September, orthopterans like grasshoppers and crickets increased in prevalence.
This flexible, opportunistic foraging allows whippoorwills to exploit whatever insects are most abundant during different parts of the breeding season. It may also help the birds obtain optimal nutrition at different life stages or times of energy demand.
Habitat and Range Effects
Whippoorwill diet varies somewhat across their breeding range. More northern populations seem to rely more heavily on moths, while southern whippoorwills consume a higher proportion of beetles and true bugs.
There are also differences between the diet in open habitats like oak savannas compared to dense mixed forests. Whippoorwills foraging in open areas eat more moths and beetles. In denser forest habitats, flies make up a larger portion of the diet.
These habitat and range differences are likely explained by variations in insect availability. Whippoorwills are opportunistic foragers and shifts in their prey simply reflect changes in the relative abundance of different insect groups across the landscape.
Foraging Behavior
Whippoorwills use a mix of foraging strategies to find and capture prey:
- Perch-hunting – Perching on branches, posts, or other surfaces and waiting for prey to approach.
- Aerial hawking – Catching insects during short flight sallies.
- Hover-gleaning – Briefly hovering to pick prey off of surfaces.
- Ground-foraging – Plucking insects like moths from the ground.
Perch hunting and aerial hawking are the most commonly used techniques. Whippoorwills will vigilantly scan their surroundings from an elevated post looking for prey movement. When an insect is spotted, they quickly launch into flight with rapid wingbeats to seize the prey. The large, gaping mouth allows them to deftly scoop up insects while maintaining speed and flight agility.
Whippoorwills most actively forage during twilight hours around dawn and dusk. This correlates with peak activity periods for many flying insects. They roost and rest during the day, conserving energy to hunt all night during the breeding season when food demands are high.
Drinking and Dietary Water
Like many birds, whippoorwills get most of the water they need from their insect prey. Each insect provides a small amount of fluid. Whippoorwills also sometimes drink while flying slowly over water sources.
They are not entirely dependent on free water though, and can get adequate hydration from their food when flying insect activity is high. During hot, dry conditions they may seek out more water sources to maintain fluid balance. Access to drinking water can be important for cooling and hydration, especially during incubation and chick-rearing.
Energy and Nutrition
Insects provide whippoorwills with ample energy (calories) to fuel their high-activity lifestyles. Insects have a high fat content relative to other prey. The caloric density from a diet based on moths, beetles, and other flying insects gives whippoorwills the energy they need for breeding, migration, and nightly foraging.
In terms of nutrients, insects provide whippoorwills with high levels of protein for growth and development. Essential amino acids for building muscle, feathers, and organs all come from whippoorwill’s insect diet. Insects also provide other vitamins and minerals like iron, magnesium, and zinc.
By targeting insect prey at different life stages, whippoorwills can obtain optimal nutrients. For example, caterpillars and fly larvae contain more fat for energy needs. Adult insects offer more protein for breeding birds.
Nestlings and Fledglings
Adult whippoorwills feed their young by regurgitating insects for nestlings and fledglings. The male parent does most of the hunting, capturing soft-bodied flying insects like moths and flies. He returns to the nest and regurgitates this insect slurry for the nestlings to consume.
Later, both parents continue to deliver regurgitated insects to fledglings that have left the nest. Fledglings first focus on easier prey like moths and flies before shifting to more evasive insects. Within two weeks of leaving the nest, fledglings are adept at capturing insects on the wing.
Providing young whippoorwills with high protein from insects supports rapid growth of muscle, organs, and feathers. It allows young birds to fledge within 17-20 days, relatively quick for the nightjar family. Access to adequate insect prey during these crucial weeks is essential for young whippoorwills.
Captive Diet
In zoos, rehabilitation facilities, and wild bird aviaries, captive whippoorwills are fed a varied insect-based diet. Common foods include:
- Mealworms
- Waxworms
- Crickets
- Roaches
- Moths
- Fly larvae
These insects are bred commercially for bird and reptile feeding. Facilities ensure the prey insects are “gut loaded” meaning they are fed high-quality diets to maximize their nutritional value. A calcium supplement is also frequently added to the insects.
In rehabilitation settings, young whippoorwills may initially be hand-fed with tweezers or syringes. This can help stabilize their health before transitioning them back to self-feeding on live insects. Providing the ideal prey items and nutrition is critical for supporting recovery.
Adaptations
Whippoorwills have several key adaptations that aid their insectivorous lifestyle:
- Large, gaping mouths for catching insects in mid-flight.
- Sensitive bristles around the mouth to help sense and capture prey.
- Wide field of vision for spying insects.
- Cryptic plumage to conceal them as they roost during daylight hours.
- Exceptional night vision enhanced by nightjars’ unique retina structure.
- Fluffy plumage and comb-like claws for soundlessly perching on branches.
- Flexibility to enter torpor during cool weather or when prey is scarce.
These adaptations all contribute to whippoorwills being highly effective nocturnal insect hunters. From their camouflage and silent flight, to specially tuned eyesight and insect-catching beaks, whippoorwills are exquisitely adapted to thrive on an insectivorous diet.
Threats and Conservation
Whippoorwill populations have been declining over the past few decades. One major threat they face is loss of prey base from habitat loss and pesticide use. Pesticides reduce insect diversity and abundance within their breeding and foraging habitats.
Climate change may also affect insect prey either through shifts in range, altering seasonal life cycles, or increasing drought. Managing forests, agricultural areas, and suburban landscapes in ways that maintain robust insect populations will be key for whippoorwill conservation going forward.
Light pollution that artificially extends daylight hours may also interfere with whippoorwill foraging. Their crepuscular insect hunting relies on natural light cues. Maintaining darkness during night hours will support their feeding ecology.
In suburban areas, people can help provide habitat for nocturnal insects by avoiding excess outdoor lighting, using motion-triggered lights instead of dusk-to-dawn, and turning off unnecessary lights during peak whippoorwill activity in the early night.
Research Needs
More research is still needed to fully understand whippoorwill diet needs and the implications for conservation:
- How will climate change affect insect prey abundance and whippoorwill foraging?
- What specific habitats and insect communities support the highest whippoorwill breeding densities?
- Do particular insects provide critical nutrition during egg-laying and chick-rearing?
- What types of forest management best promote a diverse insect prey base?
- Can artificial light levels be tailored to maintain darkness during crepuscular foraging periods?
Answering these questions through field studies and experiments can help inform habitat management and conservation policies that will support Eastern Whippoorwill populations into the future.
Conclusion
Eastern Whippoorwills are specialist insectivores highly adapted for capturing night-flying insects. Moths, beetles, mosquitoes, flies, and other insects provide the energy and nutrients whippoorwills need to breed and raise young. Their diet shifts seasonally and varies across habitats based on insect availability. Maintaining adequate insect prey will be a key factor influencing whippoorwill resilience in the face of continued environmental changes. Understanding the nuances of their insect diet provides crucial insights into habitat management and conservation strategies that can aid these declining aerial insectivores.