American Kestrels: The Most Common Falcon in North America
Meet the American Kestrel, the most prevalent falcon in North America. These majestic birds are known for their small size, with females slightly larger than their male counterparts. What sets the American Kestrel apart is their ability to see ultraviolet light, a skill that helps them track their prey. When young kestrels take their first flights, they are closely accompanied by their parents. Interestingly, the chicks consume twice as much food as the adult birds. Instead of building their own nests, kestrels opt to use existing tree cavities or evict the current residents. Due to their popularity in falconry, especially among beginners, they have become a beloved avian species. However, the number of voles in an American kestrel’s territory greatly influences their breeding success. Unfortunately, their population is slowly declining due to the detrimental effects of insecticides and loss of natural habitats. In terms of behavior, American kestrels are monogamous and typically lay between 3 and 7 eggs. They have a clever practice of caching their kills, allowing them to save food for later. These skilled hunters perch and hover while hunting, showcasing their remarkable agility. Interestingly, male kestrels migrate farther than females during winter, showing a difference in behavior between the genders. Despite their captivating nature, these beautiful falcons have a relatively short lifespan of about 5 years in the wild. With 17 sub-species, each exhibiting unique color variations and markings, American kestrels have earned various nicknames, including sparrow-hawks and grasshopper hawks.
Physical Characteristics
Size
The American Kestrel, commonly known as the sparrow-hawk or grasshopper hawk, is the most prevalent species of falcon in North America. Despite being small in size compared to other falcons, the American Kestrel boasts impressive agility and hunting prowess. On average, adult American Kestrels measure around 8 to 12 inches in length and have a wingspan of 20 to 24 inches. They are significantly smaller than their larger falcon relatives.
Sexual Dimorphism
One interesting aspect of American Kestrels is their sexual dimorphism, which means there are visible differences between males and females of the species. Female American Kestrels tend to be slightly larger than males, with a weight difference of approximately 22–32%. While males average around 3.5–4.5 ounces, females can weigh between 4.0 and 5.6 ounces.
Ultraviolet Vision
Another remarkable characteristic of the American Kestrel is its ability to perceive ultraviolet light. This unique vision adaptation benefits the kestrels immensely in their hunting endeavors. By detecting the ultraviolet reflections given off by rodents’ urine trails, the kestrels can track their prey more effectively. This ultraviolet vision gives them an advantage in locating their primary food source—small mammals such as voles and mice, which are essential components of their diet.
Behavior and Lifestyle
Parental Care
American Kestrels exhibit notable parental care, especially during the crucial early stages of their offspring’s life. When young kestrels are ready to learn to hunt, their parents accompany them on their hunting expeditions. The adult kestrels demonstrate proper hunting techniques, teaching their fledglings to maximize their chances of catching prey. This parental guidance during the transition from dependence to independence plays a vital role in the survival and development of the young kestrels.
Feeding Habits
American Kestrels have distinct feeding habits, consuming insects, small birds, reptiles, and mammals. It’s interesting to note that kestrel chicks consume twice as much food as adult birds. To support their high metabolism and rapid growth, the chicks require a constant supply of protein-rich food. As they mature, their feeding habits start to resemble those of adult kestrels, primarily focusing on capturing small mammals and insects in their hunting territories.
Nesting
Unlike many other birds that build intricate nests, American Kestrels have a more practical approach to nesting. Rather than constructing their own nests, they search for pre-existing cavities in trees or evict current residents, such as woodpeckers. These tree cavities provide a safe and suitable environment for them to lay their eggs and raise their young. The kestrels select nesting sites that offer protection from predators and adverse weather conditions, ensuring the survival of their offspring.
Falconry
American Kestrels have earned a special place in the world of falconry, particularly with beginner falconers. Their small size, adaptability, and ease of training make them ideal candidates for those starting their journey into this ancient practice. These magnificent birds of prey showcase their prowess in hunting and demonstrate their strong bond with their human handlers during falconry displays and sport.
Breeding Success
The breeding success of American Kestrels is directly linked to the abundance of their preferred prey, particularly voles. The number of voles in a kestrel’s territory significantly impacts their reproductive success. When voles are plentiful, kestrels experience higher breeding success rates. However, when vole populations decline due to factors such as habitat changes or predation, kestrels struggle to find sufficient food resources, leading to lower breeding success rates.
Declining Population
Regrettably, American Kestrels are facing a decline in population numbers throughout North America. Several factors contribute to this decline, including habitat loss, insecticide usage, and competition with non-native birds such as European Starlings for nesting sites. These threats to their natural habitat and food sources have resulted in a gradual decline in their overall population.
Monogamy and Reproduction
American Kestrels are monogamous birds, meaning they form long-term pair bonds with their mates. During the breeding season, they engage in elaborate courtship displays, which may include aerial acrobatics and vocalizations. Female kestrels lay a clutch of 3 to 7 eggs in their chosen nest cavity. Both parents take turns incubating the eggs over a period of approximately 28 to 31 days. Once hatched, the parents collaborate to feed and protect the helpless chicks until they are ready to fledge.
Food Caching
To conserve and secure food resources, American Kestrels engage in a behavior known as food caching. When they catch more prey than necessary for immediate consumption, they store the surplus food in various locations throughout their territories. This process involves hiding the food in crevices, tree cavities, or even wedging it between rocks. This behavior allows kestrels to save resources for times when food is scarce or to feed their chicks during their early stages of development.
Hunting Techniques
American Kestrels employ an array of hunting techniques that distinguish them as skilled predators. They employ a variety of strategies, such as hovering in mid-air, scanning the ground with keen eyesight, and rapidly diving to capture their prey. Additionally, kestrels are adept at using perches, often selecting elevated spots such as trees, telephone wires, or fence posts to survey their surroundings for potential food sources. These hunting techniques showcase their agility and precision in capturing their prey.
Migration
Migration patterns vary between male and female American Kestrels. In winter, many kestrels migrate to warmer regions in search of ample food availability. It is observed that male kestrels tend to migrate farther than their female counterparts, traveling greater distances to ensure they have access to abundant food resources during the colder months. Migration allows them to adapt to changing environmental conditions and maintain their survival and well-being.
Life Cycle and Lifespan
Average Lifespan
In the wild, American Kestrels have a relatively short lifespan, averaging around 5 years. However, some kestrels have been known to live up to 10 years or even longer in ideal conditions. Factors such as food availability, predation, and disease contribute to the varying lifespans of these birds of prey.
Egg Laying and Incubation
Female American Kestrels lay a clutch of eggs once a year, typically ranging from 3 to 7 eggs. The eggs are laid in succession, with an interval of approximately 2 to 3 days between each egg. Both male and female kestrels participate in incubating the eggs, taking turns to provide the necessary warmth for successful development. This incubation period lasts around 28 to 31 days, during which the parents diligently tend to the eggs, ensuring their optimal conditions for hatching.
Chicks and Fledglings
Once the kestrel chicks hatch, they are born relatively helpless and rely entirely on their parents for warmth, protection, and nourishment. The parents work collaboratively to provide a steady supply of food to the chicks. As the chicks grow, they begin to develop their flight feathers and gain strength in their wings. After approximately 4 to 5 weeks, the young kestrels, now fledglings, leave the nest and take their first flights. During this crucial phase, their parents guide them, imparting essential hunting skills and ensuring their transition to independent hunters and survivors.
Sub-Species and Variations
Number of Sub-Species
The American Kestrel exhibits subtle variations across different regions, leading to the recognition of 17 distinct sub-species. These sub-species occur in various habitats throughout North and Central America. The differences among the sub-species primarily involve variations in plumage, with each exhibiting unique coloration and markings specific to its particular geographic range.
Color and Marking Variations
The 17 sub-species of American Kestrels showcase a diverse range of color patterns and markings. Plumage coloration can vary from shades of reddish-brown, orange, and gray to vibrant blues and greens. These variations contribute to the stunning beauty and captivating visual appeal of these birds. Depending on their sub-species, American Kestrels may exhibit intricate patterns of bars, spots, and streaks across their bodies, which add to their aesthetic diversity.
Nicknames
Due to their prevalence and distinct characteristics, American Kestrels have earned various nicknames. Common alternate names for American Kestrels include “sparrow-hawks” and “grasshopper hawks.” These nicknames often derive from the kestrels’ small size, hunting behavior, or habitat preferences. These endearing nicknames reflect the fondness and familiarity people have developed for these captivating birds of prey.