The Swainson’s hawk is a medium-sized bird of prey that is found in western North America. Its diet consists primarily of small mammals, birds, and insects. In the following article, we will take an in-depth look at the different types of prey that make up the Swainson’s hawk’s varied diet.
Small Mammals
One of the Swainson’s hawk’s preferred sources of prey are small mammals such as rodents. Studies have shown that rodents can make up anywhere from 50-90% of a Swainson’s hawk’s diet during the breeding season. The most commonly consumed rodents include voles, mice, ground squirrels, rabbits, and prairie dogs. The abundance and availability of small mammals in a particular region is a key factor influencing the Swainson’s hawk’s diet and breeding success there.
The Swainson’s hawk often hunts for small mammals in open grasslands, fields, and prairies where the rodents are more visible. Their excellent eyesight allows them to spot the movements of prey while soaring high in the air. They will then dive down swiftly to snatch up unsuspecting rodents with their powerful talons.
One rodent that is especially important to the Swainson’s hawk is the Richardson’s ground squirrel. Swainson’s hawks synchronize their migration so they arrive at their breeding grounds in the prairie regions of the western United States and Canada precisely when these ground squirrels emerge from hibernation. An abundance of Richardson’s ground squirrels means plenty of food for raising healthy chicks.
Birds
Though small mammals make up the bulk of their diet, Swainson’s hawks will also prey on smaller birds, especially during the non-breeding season when rodent populations decline. Common avian prey include larks, sparrows, quails, doves, and shorebirds. The hawks hunt for birds in open areas by spotting them while soaring high overhead. They will swoop down at speeds up to 150 mph to catch birds in flight with their talons.
One unique avian hunting strategy Swainson’s hawks employ is intentionally flushing flocks of roosting shorebirds off the ground so they can grab them in mid-air. This behavior has been observed along coastal regions where large flocks of shorebirds gather.
Insects
Though not as substantial a food source as mammals and birds, Swainson’s hawks do consume some insects to supplement their diet. They are opportunistic predators and will feed on large grasshoppers, cicadas, beetles, and crickets when the opportunity arises. Swainson’s hawks have been observed catching flying insects in mid-air by sallying out from a perch. But they will also snatch up insects from the ground as they walk along open fields. Consumption of insects tends to increase during the post-breeding season when insect numbers are higher and migratory flocks of hawks form.
Amphibians and Reptiles
On rare occasions, Swainson’s hawks will prey on amphibians like frogs and toads, and small reptiles such as lizards and snakes. However, these make up only a very small percentage of their overall diet. Snakes in particular are likely avoided as prey because of the potential danger they pose to the hawks when caught.
Carrion
Though they primarily hunt live prey, Swainson’s hawks are also opportunistic scavengers. They will feed on animal carcasses of both mammals and birds if they are readily available. Roadkill is a common source of carrion that these hawks will utilize when discovered along open roads.
Regional and Seasonal Diet Variation
The diet of Swainson’s hawks can shift both regionally and seasonally depending on what prey sources are most abundant at a given place and time. Here is a table summarizing some of the key dietary variations:
| Region | Breeding Season Diet | Non-Breeding Season Diet |
|---|---|---|
| Western North America prairies | Mostly small mammals like ground squirrels and voles | Higher bird consumption and more insects |
| Southwestern U.S. and Mexico | Small mammals as well as reptiles like snakes and lizards | Shift to insects, birds, and carrion |
| California Central Valley | Primarily ground squirrels and other rodents | Birds, rabbits, insects, some fruits and grains |
| Agricultural regions | Ground squirrels, pocket gophers, voles | Grain, small birds like sparrows, carrion |
As the table shows, small mammals consistently dominate the diet during breeding season across regions, while the non-breeding diet shows more diversity including more birds, insects, reptiles, and plant material depending on location and seasonal availability.
Hunting and Foraging Behaviors
Swainson’s hawks exhibit a variety of hunting strategies and behaviors tailored to capturing different types of prey:
- Soaring at high altitudes searching for prey movement below.
- Sudden stooping dives to snatch prey on the ground.
- Low cruising flight around grasslands to flush and catch rodents.
- Quick sallies from perches to catch flying insects and birds.
- Foraging for insects on foot walking along the ground.
- Snatching of nestling rodents directly from their burrows.
- Caching uneaten food in trees or grass for later feeding.
- Opportunistic scavenging of carrion and roadkill.
Their varied hunting strategies allow Swainson’s hawks to exploit many prey sources and adapt to changes in prey availability throughout the seasons. The large appetite of these energetic raptors keeps a constant check on rodent and insect populations where they hunt.
Meal Size and Consumption Rates
Since Swainson’s hawks feed on relatively small prey like rodents and insects, they must capture multiple prey items each day to meet their dietary needs. However, exact meal sizes and daily consumption rates can vary significantly depending on the hawks’ energy requirements at a given time.
On average, Swainson’s hawks will consume about 3-5% of their body weight per day. For an average adult hawk weighing around 2 pounds, this equals approximately 60-100 grams of food per day. They tend to gorge themselves when prey is abundant, then go days without eating when food is scarcer.
Nestlings and fledglings have much higher energy demands and can consume up to one and a half times their own body weight each day as they grow. For comparison, an adult human would have to eat around 130 pounds of food per day to equal the same relative consumption rate!
The small mammals, birds, insects, and other prey the hawks catch are usually swallowed whole. Their powerful stomach acids digest everything, leaving only indigestible fur, bones, and teeth to be regurgitated back up in pellets.
Adaptations for Hunting and Eating Prey
Swainson’s hawks have several key physical and behavioral adaptations that make them effective hunters and consumers of a wide range of prey:
- Sharp talons to swiftly grab and kill prey.
- Hooked beak well-suited for tearing flesh.
- Curved talons ideal for snatching and holding onto slippery fish.
- Strong wings for sustained soaring flight to search for prey.
- Acute long-distance vision to spot prey movement from great heights.
- Powerful speed and agility in flight to dive and capture evasive prey.
- Highly expandable stomach and esophagus to swallow large prey whole.
- Strong stomach acids to completely digest bones, fur, chitin, and feathers.
- Ability to regurgitate indigestible parts of prey back up as pellets.
- Skill hunting cooperatively in groups or family units when prey is abundant.
Together these adaptations allow Swainson’s hawks to thrive across diverse habitats and exploit many different food sources from dangerous rattlesnakes to tiny grasshoppers. The flexibility of their predatory skills and digestive system contributes to their success across western North America.
Impacts of Prey Availability
The availability and abundance of the Swainson’s hawk’s preferred prey species can have significant impacts on their population numbers, distribution, reproductive success, and migratory patterns throughout their range.
When small mammal populations crash or decline, Swainson’s hawks have lower breeding success and chick survival rates in those areas because of food shortages. Cycles of prey booms and busts, driven largely by changing climate and vegetation conditions, are a key factor influencing Swainson’s hawk population levels from year to year.
Loss of suitable hunting habitat, such as conversion of open prairies to cropland, can also limit access to prey and force Swainson’s hawks to alter their migratory routes and destination wintering grounds. Protecting sufficient feeding habitat across their range is crucial for maintaining stable Swainson’s hawk populations into the future.
Agricultural practices also impact prey availability. While some rodent species thrive in croplands, pesticide use and mechanized farming can decimate their populations. Sustainable agricultural methods that support healthy small mammal communities are beneficial to maintaining Swainson’s hawks’ main food source.
Role of Swainson’s Hawks in the Food Chain
As predators of small mammals, birds, reptiles, and insects, Swainson’s hawks play an important ecological role in helping regulate prey populations and prevent over-grazing or crop destruction:
- Rodent predation limits potential damage to crops and vegetation.
- Insect predation provides natural pest control of damaging species.
- Limits large population surges and stabilizes fluctuations of prey species.
- Reduces spread of disease by sick prey animals.
- Scavenging of carrion helps clean up the landscape.
- Prey leftovers provide food sources for other wildlife.
- Stimulates prey avoidance behaviors that shape ecosystems.
However, Swainson’s hawk populations themselves are also vulnerable to declines when prey becomes scarce, habitat is lost, or pesticide use decreases available food. Maintaining sustainable populations of Swainson’s hawks and their prey is important for preserving balanced and healthy ecosystems.
Threats to Swainson’s Hawks from Prey Contamination
While feeding on small prey gives Swainson’s hawks access to abundant food sources, it also puts them at risk of accumulating dangerous levels of toxins and other contaminants that may be present in the prey animals. Some key threats include:
- Bioaccumulation of pesticides applied to crops that rodents feed on.
- Ingestion of lead bullet fragments in gut piles of prey shot with lead ammunition.
- Consumption of insects or rodents with high toxin levels.
- Eating chemically contaminated roadkill.
- Increased mercury concentrations from eating birds or fish.
These toxins can cause illness, reproductive issues, or even death in Swainson’s hawks. Minimizing use of persistent and bioaccumulative pesticides, switching to non-lead ammunition, and reducing chemical runoff into waterways can help protect both the hawks and their prey.
Conclusion
In summary, Swainson’s hawks are fierce predators that primarily hunt small mammals, birds, and insects across a variety of open habitats in western North America. Abundant prey availability strongly influences their breeding success and population numbers. They play an important role in balancing populations of rodents, reptiles, and invertebrates within their ecosystem. However, they face risks from contamination in the food chain and habitat loss. Maintaining suitable habitat and prey resources is key to preserving healthy Swainson’s hawk populations into the future.
