The American Kestrel breeding season in North America last from March through July. The initiation of the breeding season is influenced by the latitude. Kestrels in the south start the breeding cycle earlier than kestrels in the north. This article delves into details of the American Kestrel’s breeding cycle, details of its courtship display, mating, the role of the male and female, and second broods. Let’s dive and see what I have put together.
American Kestrel Breeding Season: Phenology
American Kestrel
Breeding
Nest
Eggs
Chicks
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The breeding season of North American Kestrels varies with the latitude at which a kestrel population breeds. As a general rule, kestrels in lower latitudes, such as the Southern United States, initiate the breeding season earlier than their counterparts in higher latitudes, such as Canada. This is because lower latitudes typically experience milder winters, enabling southern kestrel populations to initiate egg-laying earlier than their northern counterparts. Kestrels in northern latitudes have narrower breeding seasons than their southern counterparts.
Latitude and timing of breeding
Latitude significantly influences the migratory status of American Kestrel populations and the timing of breeding. Kestrels breeding in the northernmost regions, particularly in Canada and Alaska, are considered obligate migrants, meaning they must migrate annually to escape harsh winter conditions.
Yellow markers indicate the initiation of egg-laying.
– Egg-laying in Florida begins the first week of March.
– Egg-laying in Iowa: Begins the third week of March.
– Egg-laying in Saskatchewan begins the last week of April.
As latitude decreases, the migratory behavior of kestrels transitions from obligate to facultative, and eventually to resident. In lower latitudes, such as the southern United States and Mexico, kestrels exhibit facultative migration, meaning that some individuals may migrate while others remain year-round residents.
This flexibility is primarily driven by local environmental factors, such as food availability and winter temperatures. In areas with mild winters and abundant food sources, some kestrels may forego migration and remain in their established territories.
Comparative studies conducted in Saskatchewan (Canada), the State of Iowa, and Floria (USA) illustrate the variation in the initiation of the breeding season on North American Kestrels. (G. R. Bortolotti, D. E. Varland and JAS; cited in Smallwood and Bird 2020). The study found that:
- Egg-laying in the State of Florida begins the first week of March and peaks between March 20 and Apr 5.
- Egg-laying in the State of Iowa begins the third week of March | Peaks between April 15 and April 30.
- Egg-laying in Province of Saskatchewan (Canada) begins the last week of April | Peaks between May 15 and May 30.
The active breeding period lasts between 55 to 60 days. This is the time between the day the female lays the first egg and the day the first chick leaves the nest. However, kestrels in North America are breeding in a staggered fashion between the months of March through July.
Initiation of the breeding cycle in migratory and resident kestrels
The initiation of the breeding season is slightly different among migratory kestrel populations and their year-round resident counterparts.
Migratory kestrel Populations
Males arrive first and either head to the nesting site where they bred the previous year or explore the general area for suitable territories and cavities. Females arrive later at the territory and cavity they used the previous year, where they reunite with the male they bred with. Alternatively, females scout the general area for potential mates, their territories, and suitable cavities.
The pair may settle for last year’s cavity or scout potential cavities. The male leads the female to the cavities he has chosen and the pair settles for one. It is uncertain whether she makes the final decision to settle for one nesting site or it is a mutual agreement.
Resident kestrel populations
Breeding pairs within the resident kestrel population maintain the same territory, actively protecting their breeding cavities from potential takeover by other animals. These cavities, used for breeding, may also serve as roosting sites for resident kestrels during non-breeding periods.
American Kestrel breeding range maps
Distribution during the breeding season
During the breeding season kestrels move northward from southern United States and Mexico. During this part of the kestrel’s breeding cycle, they occupy most of Canada and Alaska.
Distribution during the nonbreeding season
After the breeding season is over, American kestrels begin to migrate to their wintering grounds. Some kestrels will only migrate short distances, while others will migrate thousands of miles. Wintering grounds for American kestrels include Mexico and Central America.
The areas in brighter red represent higher concentration of kestrels. Maps generated by eBird Science.
The areas in brighter blue represent higher concentrations of kestrels.
Courtship Displays, Pair formation, and mating.
Your passage is quite clear, but I’ve made a slight adjustment for conciseness:
At the start of the breeding season, American Kestrels engage in diverse courtship rituals, such as aerial acrobatics, vocalizations, and the exchange of food. Mating occurs shortly after the pair forms or decides to breed together, whether they are establishing new pairs or maintaining bonds among already established pairs.
Some of these displays are performed more intensely during the initiation of the breeding period, but are also performed throughout the time kestrels are incubating eggs and caring for the young.
Courtship Displays
The following are descriptions of breeding courtship behaviors observed in the field.
Fluttering wingbeat glide
I call the “fluttering wingbeat glide” a “Staple” courtship display because it is performed by the male and female and repeated in most rituals displays.
The “fluttering wingbeat glide” consists of a buoyant flight by either sex with short, shallow, and quick wingbeats while keeping the wings straightened out and stiff. This courtship display is performed during the following occasions, most of which are accompanied by calls by the male:
- The male does a fluttering wingbeat glide as it flies towards the female perched nearby and prepares to perch next to her.
- Both the male and female perform the fluttering glide when they unexpectedly meet in the air near the nesting cavity or popular perches where they eventually land.
- The female performs the fluttering glide while the male performs a series of sequential dives and ascents toward her, calling repeatedly. The male can also perform sequential dives and ascents at the female while she is perched.
- The male uses the fluttering glide to entice the female to follow him and inspect a nest site. He may use food or not to entice her to a nest site.
- The male brings food to the female, flying normally until he is within sight of her, at which point he performs the fluttering glide flight. She can meet him in mid-air to take the food or wait for him to perch next to her. If the female is inside the nesting cavity, the male calls and she rushes out to meet him, and they flutter glide together to a perch. She can also accept the offer in mid-air and fly with him to a perch.
- The male performs the fluttering glide as a prelude to mating. He almost always lands on her to copulate, rather than jumping on her while perched.
Pair formation
A sign that a pair has been formed and the pair is about to initiate a breeding attempt is when the female begins to accept the food offered by the male. It is unclear if acceptance comes after a nest site has been established or before that.
How do American kestrels mate?
American Kestrels mate through a process that involves food offerings, bowing, and cloacal contact. The female’s readiness is signaled by bowing and raising her tail, prompting the male to perform a fluttering glide and land directly on her. Copulation is brief, lasting only a few seconds, and concludes with cloacal contact.
Do American Kestrels mate for life?
Whether American Kestrels mate for life depends on the population. In sedentary populations, pairs often remain together and use the same nesting cavity for multiple breeding seasons. However, in migratory populations, it is unclear whether pairs mate for life.
Males return to their wintering grounds first, and females arrive later. While males typically return to the same territory, it is unknown whether they mate with the same female from the previous year.
Communication during the breeding season
American Kestrels communicate constantly during the courtship display period prior to the initiation of breeding activities. They communicate through vocalizations and body language. Males will vocalize during courtship rituals and females will respond with calls of their own.
Once a pair begins laying eggs vocal communications appear to subside giving way to communication through body language, such as head-bobbing and tail-flicking.
The Role of each Sex during initiation of the breeding Season
Both male and female American Kestrels play a role in initiating the breeding season. Males will perform aerial displays to attract females to his territory and potential nesting cavities. Females respond by staying in the area and responding to the males courtship displays.
A sign that a female is interested in such male and territory is when she follows the male to check together the potential nesting sites. During this time the male does much of the courtship and calls and she responds with calls of her own.
A sign that a pair has been formed is when the female accepts the food offered by the male. This establishes the pair bond and subsequent breeding activities follow.
Do American kestrels have a second brood in a single breeding season?
In some cases, American Kestrels may produce a second brood during the breeding season. If the first clutch is lost, the female may lay a second clutch of eggs. The timing of the second brood will depend on when the first clutch was lost.
In general, migratory American kestrels in temperate regions or high latitudes are less likely to have time for second broods than kestrels in lower latitudes. Kestrels in Canada and Alaska, the northernmost regions of American Kestrel breeding grounds, have been documented raising second broods, but it is less common than in warmer regions.
This is because the breeding season in Canada is shorter than in the southern United States and Mexico. Additionally, food and nesting sites may be more scarce in Canada, which can make it difficult for kestrels to raise two broods in a single breeding season.
In a study conducted in Saskatchewan, Canada, researchers found that 12% of American kestrel pairs raised two broods. This was compared to 25% of pairs in a study conducted in Texas. The researchers concluded that the shorter breeding season and the scarcity of food and nesting sites in Canada were the main reasons why kestrels were less likely to raise two broods in that region.
However, there is some evidence that American kestrels in Canada are becoming more likely to raise second broods in recent years. This may be due to a number of factors, including climate change, which is causing the breeding season to start earlier and end later. Additionally, there may be more food and nesting sites available in some parts of Canada than there were in the past.
References
- Ardia, D., K. Bildstein. 1997. Sex-related differences in habitat selection in wintering American kestrels, Falco sparverius. Animal Behavior, 53: 1305-1311.
- BirdLife International, 2012. “Falco sparverius” (On-line). IUCN Red List of Threatened Species. Accessed November 01, 2013 at http://www.iucnredlist.org/details/22696395/0.
- Johnsgard, P. 1990. Hawks, Eagles, and Falcons of North America. United States: Smithsonian Institution.
- Smallwood, J. A. and D. M. Bird (2020). American Kestrel (Falco sparverius), version 1.0. In Birds of the World (A. F. Poole and F. B. Gill, Editors). Cornell Lab of Ornithology, Ithaca, NY, USA.
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