For owls, as with any species, reproduction is important because it gives them the opportunity to pass genes from parents to offspring. Owls are generally monogamous and although there are differences from one species to another, the same mates can mate for mating purposes for several years. Food availability or prey abundance is an important factor for owls that determines the breeding and rearing of juveniles. Although some species generally enter breeding during the spring period, the breeding and growth of the offspring often coincides with the availability of food. Other factors that play an important role in determining breeding among owls include hunting risk, agricultural activities, favorable weather conditions, suitable mate, and disease, among others.
Factors Affecting Reproduction Among Owls
There are factors that affect sexual reproduction among owls and they are as follows:
• Food availability,
• Weather conditions;
• Feather coloring,
• Hunting risk,
• Existence of spouse,
• Habitat quality,
• Placement of nest boxes,
The presence of prey is an important consideration in owl breeding as it affects the body condition of the birds. Therefore, it can be considered as the most important factor affecting reproduction among owls. The presence of prey animals not only affects the body condition of the bird, it also affects the survival of both parents and offspring. The availability of food is determined by other factors such as habitat, climate and agricultural activities.
It has been shown that the reproductive success of barn owls increases with the proportion of mice in the diet and decreases with the proportion of mice in their diet. Voles appear to have some advantages over mice as owls’ favorite potential prey, and flywheels weigh three times that of mice. An owl may have to expend three times the energy to catch the equivalent weight of mice and catch a vole. The presence of field mice is positively correlated with successful breeding among owls and the number of offspring produced. Additionally, grip size and juvenile survival correlate positively with the presence of field rat densities.
Owls need food or energy in cold and snowy weather due to the need for body temperature regulation. Foods that can be channeled for reproductive purposes are definitely directed to survival first, unless they are sufficient to meet both needs. Also, hunting is scarce and difficult to find in these cold weather. It might seem that the effect of cold weather will not be felt by owls because of their feathers, but it has been reported that owl feathers do not provide as much insulation for the body as expected. Also, owls are known to have less oil reserves so they can face harsh weather conditions. In summary, inclement weather, particularly cold weather, is an important factor limiting owl breeding due to the availability of prey and increased nutritional needs for owls.
It has been reported that in the winter, barn owls are responsible for the major change in reproductive performance. Reproduction decreases drastically during the winter months, resulting in large mortality rates in potential breeders. It also inhibits prey capture and limits prey accessibility due to the owl’s greater energy requirement to maintain body temperature necessary for its survival. Breeding success in owls is sometimes higher in further northern latitudes. It has been shown that the reproduction of the northern spotted owl (Strix occidentalis caurina) is negatively correlated with winter precipitation, while the California spotted owl (breeding Strix occidentalis occidentalis) is positively associated with precipitation. It has been observed that the most important factors affecting breeding among owls are weather conditions and prey availability.
Coloring of feathers
It has been reported that differences in feather coloration tend to cause behavioral, physiological, and fitness differences among owls. Down coloration is associated with improved immune response in owls. It is an important factor influencing male owls’ decision on mate selection. Research findings showed that more spotted female owls decreased in nesting associated with pups with enhanced immune response and blood-sucking flies (Carnus haemapterus). It is natural for male owls to choose heavily stained females, taking into account factors such as having higher breeding quality.
Female hair color is positively associated with parasite resistance, and it has been suggested that heavily spotted female owls are an estimate of low parasite fertility. Moreover, hair spot is defined as an inherited trait. The male may choose this trait for breeding as an indicator of the female genetic quality, a hereditary trait that predicts the offspring’s ability to resist parasites.
For male owls, lighter male barn owls have been reported to have lower reproductive success than reddish-brown males and do not feed offspring as much as reddish-brown ones. However, barn owls in the Middle East are observed to be lighter in color than in temperate regions. Darker owls have been reported to have larger wings and tails and consume less Muridae than dark reddish owls that consume more Cricetidae.
Another important factor affecting the reproduction and survival of the offspring among owls is the risk of hunting. The main predator of owls is the log raptor goshawk, Accipiter gentilis. Daily predation by birds of prey can account for about 73% of natural pied owl deaths. A research report found that predation is more biased towards female reproduction. Breeders and parents may be more exposed to predation as they spend more time out of the nest feeding their offspring. In years of predation, it makes sense to reduce breeders’ vulnerability to the risk of hunting by minimizing the amount of food allocated to the offspring. They can only reduce the distribution of food by reducing breeding rates or putting in smaller clutches. No wonder, then, why reproductive propensity was reported to be high in years of low predation. It has been noted that owls with small claws that contain 1-2 eggs that breed in areas at risk of predation are less likely to complete the breeding attempt than owls with larger paws that breed in areas with less exposure.
In some parts of the world, especially in the UK, goshawks begin to appear on soils, burrows and buildings in late March and April. This is when owls in most cases are already devoted to breeding. Therefore, if exposed they may be threatened with not completing the reproductive attempt. It is observed that breeding parents and those who produce more offspring per breeding attempt are generally more vulnerable to the risk of predation than non-breeding parents or those producing less offspring. It is common practice for long-lived parents to reduce their vulnerability in years when the risk of predation is high. They minimize their vulnerability in three basic ways and these are as follows:
• Avoiding reproductive activities completely,
• By reducing the number or quality of the offspring produced,
• Neglecting the reproduction attempt at an early stage,
Age has been shown to slightly affect sexual preproduction among owls. The propensity to breed increases slightly as female owls age, but this has only been observed in parents who had successful juvenile chicks in the previous year. It has been reported that female owls that have successfully hatched young chicks in previous years are more likely to breed as they age, compared to those without baby chicks. It has been observed that survival and reproduction rates depend on age.
The decline in population size and the extinction of many wildlife species are due to emerging infectious diseases. And it has been noted that the spread of these diseases is facilitated by the movement of carriers and pathogens resulting from environmental change due to climate and human change. Threatened species may be pushed to extinction as a result of reduced reproductive performance or direct death.
Since owls undergo sexual reproduction, the availability of breeding mates is crucial to breeding and its success. In addition to the availability of the spouse, it is a matter of closeness to the spouse. Familiarity between spouses has been observed to increase reproductive performance among owls.
Reproductive distribution, a movement between successive breeding sites, has been reported to offer owls the opportunity to improve reproductive performance by avoiding inbreeding among owls, as well as moving to a better breeding ground or pairing with a better mate. However, dispersal may result in reduced reproductive success, as there is no guarantee that dispersed individuals have better territories or mates.
Owls are sometimes picky when it comes to breeding grounds. Barn owls are reported to prefer to breed in nesting boxes away from roads. Breeding in nest boxes close to roads can affect the reproductive process as a result of traffic accidents as well as disturbances. Variations in the breeding performance of barn owls in the Middle East have been associated with differences in habitat characteristics surrounding their nest boxes.
Intensive farming practices have been observed as one of the reasons for the decline of owls, causing less grain in the field for small mammals to feed, reducing the availability of game animals for owls. The fewer ditches and boundaries available to rodents are another factor affecting the owl population.
Placing nest boxes
The presence of nest boxes in areas that are not suitable for agriculture can be observed in areas with field plants, which will increase the availability of game animals. It has also been observed that it may limit the availability of prey animals for owls. It has been suggested that barn owls prefer to breed in areas with arable fields due to the availability of various owl diets in the micro-habitat.
Author: Ozlem Guvenc Agaoglu