Text/Dolphin
Type II has always been a topic of conversation among biologists. Whether it is the gorgeous feathers of male peacocks or the spectacular horns of male deer, type II is often a complex product of environmental stress and sexual selection.
Carnivores are the overlords of the land, while birds of prey of the order Hawks, Falcons, and Owls are the masters of the skies, and they face similar challenges. However, the sexual ii manifestations of birds of prey and beasts are diametrically opposed. Most of the beasts are larger in males, while most birds of prey are larger in females. What causes this phenomenon?
A scarred male polar bear is trying to capture the hearts of females; polar bears are one of the most prominent non-pinniped carnivores of type II in the mustela family and cat family, and the fights between males are often very intense
The degrees of raptor and type II of raptor vary widely from breed to species, but these are not without regularity. First, let's look at the Raptor. In a 2005 study, Kruger summarized the sexual dichotomy of eagles, falcons, and owls, in short, the more difficult it is for a bird of prey to catch, the smaller the male size.
For birds of prey, the most difficult prey to catch is other birds, and the bird of prey is indeed the most prominent type of raptor. Among them, the Accipiter ventralis ( Accipiter ventralis ) , which is found in the tropical forests of South America , is probably the most prominent type II of prey , with an average male wingspan of only 53 % of the female.
Other birds of prey such as birds, bats, monkeys, squirrels and other fast, vigilant and agile prey, such as the eagle-shaped sparrowhawk, goshawk, crested eagle, Ai's eagle, crowned eagle, etc., as well as falcons, peregrine falcons, grey-backed falcons, etc., male wingspan is often less than 80% of the female wingspan.
Manta falcons, living in the rainforests of the Americas, feed on a variety of birds and bats, and their male wingspan is 61% of that of females; the picture shows a manta falcon couple together, it is not difficult to see that the female on the right is not only larger, but also much larger
As the difficulty of catching prey decreases, the size of the raptor type II also decreases. Birds of prey catch small prey on the ground, such as rats and rabbits, are much easier to catch than difficult birds. In the case of the order Hawks, many eagles, eagles, snake eagles and other birds of prey that feed on ground prey male wingspan is often greater than the female wingspan of 80% or even 90%. The same is true of various falcons and owls, which feed mainly on small mammals, reptiles and large insects.
Scavenger raptor food is more readily available, so the males of scavenging birds such as crested falcons, vultures, and American vultures are almost exactly the same size as females, and many American vultures have even larger males than females. The male Vultur gryphus has a wingspan of 126% of the females, the largest proportion of males of all birds of prey.
A pair of Andean condors can be seen to be slightly larger on the right; and the Andean condor is also one of the few birds of prey with significant differences in gender signs, and the males have obvious meat crowns
The degree of carnivorous purposeful type II is also correlated with the habits of species. Law's 2019 study showed that the degree of purposeful type II of terrestrial carnivorous meat was related to the degree of eating habits and sociality.
Overall, carnivorous males with high degrees of solitude and carnivorousness are relatively larger. The main ones that meet this definition include the vast majority of cats, as well as the subfamily Mustela, the subfamily Nest ferret, and the subfamily Mink in the mustel family. Familiar tigers, leopards, cougars, weasels, etc., males are significantly larger than females. Among terrestrial carnivores, the most prominent type II is the Japanese ferret (Mustela itatsi), whose average female weight is only 30% of that of males.
Social carnivorous carnivores such as jackals and wolves are generally relatively less sexually type II, while omnivorous, plant-feeding, insectivoretic, and fish-eating carnivorous orders are even less so. Of course, the above two laws only represent a general trend, and there are many exceptions.
The subfamily Ferret is one of the most prominent taxa of the entire carnivorous order, and the Japanese ferret is an extreme presence even in this taxon, and its male-female body size ratio is as large as that of seal sea lions; the Japanese ferret is closely related to the weasel common in China, but the tail is relatively longer
The same carnivores, what causes the birds of prey and beasts of prey to have completely different sexual types? In fact, like all animals, the sexual type ii of birds of prey and beasts is the result of a combination of natural selection and sexual selection, and the difference between the two reflects their differences in reproductive strategies.
Let's start with the Raptor. In order to explain the sexual type II of birds of prey, scientists have proposed some hypotheses.
The first hypothesis is that bird-eating birds of prey are larger because they are fierce, and that males may mistake the female for potential prey during courtship chases, resulting in injuries to their mates, and that females are larger in size to protect themselves. But in the observation of raptor breeding, scientists found that the married life of raptors is often very harmonious, and there is no such "domestic violence". What's more, if bird-eating raptors do treat their mates as prey, larger females will obviously threaten the safety of males as well. This hypothesis is therefore clearly wrong.
The second hypothesis is that birds of prey are larger females because they are females competing males, and that they are larger in size in order to gain advantage in competitions. It is not uncommon for females to compete with males in birds, but birds with this habit tend to have more vivid females than males. The body colors of raptors tend to be similar, and among species with differences in body color, smaller males have more colorful feathers. Therefore, this hypothesis is also untenable.
Two brightly colored females (Rostratula benghalensis) and darker males
A third hypothesis suggests that the reason male raptors are smaller is the way they court. This view holds that male raptors rely on aerial performances to attract females, and since females prefer more agile males, sexual selection makes smaller males more successful in breeding competition.
A similar phenomenon does exist in birds. Male hummingbirds have extremely gorgeous feathers, but tend to be smaller than plainly colored females, and this is precisely because male hummingbirds attract the opposite sex and do not rely solely on color, and their skills in flying in the air are also an important selection criterion for female hummingbirds.
This hypothesis sounds plausible. However, there are significant differences between raptors and hummingbirds in their strategies for feeding their offspring. Male hummingbirds mate with as many females as possible and do not participate in the upbringing of their offspring. The male raptor, on the other hand, is a model father of the animal kingdom, not only feeding the young during the breeding season, but also feeding the female when she incubates her eggs and nests. Moreover, the husband and wife relationship of raptors is generally relatively stable, and most raptors will choose a mate from the previous breeding season. Therefore, courtship may not be the root cause of the male and female of the raptor.
Archilochus colubris with males on the right and females on the left, weighs about 90% of the females
So what exactly causes birds of prey to be large and female? While it's hard to tell exactly what exactly is "why" of a feature in natural evolution, scientists seem to have a definitive answer to this question after multiple studies. Multiple studies have shown that smaller sizes not only make male raptors better hunters, but also better breadwinners.
Although raptor couples invest heavily in raising their chicks, male raptors tend to take on most of the hunting tasks. Early in the breeding season, female raptors are often required to stay in the nest to incubate their eggs and protect their nests, while males provide food for their mates and chicks. It is not until the chicks increase in size later in the breeding season that the female begins to share the hunting task with the male.
Many readers may think that the larger a carnivore is, the more capable it is to hunt. This is not the case. Although the male eagle is small, they are also excellent hunters, and due to the strong lethality of the raptor, it is fully capable of hunting tasks, and its efficiency is even higher than that of the female eagle, because it is more agile. This advantage is not important for predatory ground animals and scavenger birds of prey, but it is especially important for birds of prey that are more difficult to hunt, which partly explains that the sex type II of bird-eating birds of prey is particularly prominent.
Moreover, the smaller males themselves have smaller appetites, and after catching prey, they can also leave more to their wives and children, which can be described as open source and throttling.
The male kestrel gives the prey to his more modest-looking mate, while the female rushes to bring the prey back to the nest
However, although the male eagle is a hunting expert, the larger female eagle still needs to defend the territory. A 2004 study by McDonald and his team found that the average size of female raptors involved in breeding was larger than the average of females in the population, while males were no different from overall levels. Territorial conflicts between female raptors are common, so they speculate that larger females are more likely to own and hold good territory, increasing reproductive success, and this evolutionary pressure prompts female raptors to grow in size.
At the same time, the difference in body size between male and female raptors can also effectively reduce the vicious competition between the sexes during the non-breeding period. For all animals, their strongest competitor is always their own kind. Male and female raptors in the shared territory can choose different prey during the non-breeding period because of the obvious difference in body size, and the male selection is wider and more elastic in general, which can effectively avoid competition.
A pair of sparrowhawks; the female, though more modest in color, is much larger
The same logic applies to beasts of prey. Law's research points to two main drivers of carnivorous type II: sexual selection due to males competing for territory, and ecological niche distinctions between the sexes.
Unlike monogamous birds of prey, solitary beasts of prey breed mostly polygamous, and males often need to defend a large territory that includes multiple female territories, and this pressure of sexual selection forces them to evolve larger sizes to face same-sex challengers.
The sole beast's responsibility for raising its cubs is generally entirely the responsibility of the female, and they are therefore required to take on the difficult task of hunting for themselves and their cubs. Like male raptors, female solitary carnivores may be slightly inferior to males in hunting very large prey, but their smaller size in exchange for agility, speed and concealment make them more comfortable than males in facing richer small and medium-sized prey, and their smaller size can also leave more food for their cubs, so as to achieve open source and throttling.
At the same time, due to the difference in body size between male and female predators, they can also avoid vicious competition by choosing different prey.
A leopard couple; the black males in the rear are significantly larger than the regular color females in the front
This is especially important for slender ferrets that feed on burrowing prey. For them, relying on their slender stature to drill into rodent burrows is an important way of hunting. Female ferrets are smaller and can dive into smaller holes, so they have more prey options. For female ferrets who are pregnant with hexacarp, the small size also ensures that their hunting during pregnancy is not too affected.
Interestingly, stout carnivorous ferrets such as the American badger rely mainly on digging and hunting, so they do not need to drill holes, and their sexual type II is relatively low.
In contrast, for social predators that eat "big pot rice" and whose reproductive strategies are mainly monogamous or mating at will, such selection pressure is less important. This is especially true for omnivorous, plant-fed, insecticidal, and fish-eating carnivorous orders.
The ferrets that hold voles are even slimmer than their prey; although stoats are known for killing burrowing rabbits in great proportion to themselves, their main prey is a variety of rats
In summary, the key reason why raptors are larger females and predatory males are larger is that their social division of labor is different. Whether it is a solitary beast or a bird of prey, it is a smaller body with strong hunting ability to raise a family, and a larger body fights fiercely. Therefore, among them, those responsible for providing food for the cubs are relatively small, while those responsible for grabbing the land are often larger.
In the birds of prey, it is often the male who is mainly responsible for raising the family, the female bird is mainly responsible for the external fight, so it is the female and the male, and in the feline, ferret and other solitary predatory beasts, the female beast alone undertakes all the tasks of the baby, and the male is responsible for grabbing the territory, so it is the male and female. Although there are no shortage of individual exceptions, the overall law is obviously like this.
bibliography
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McDonald, Paul G., Penny D. Olsen, and Andrew Cockburn. 2004. Selection on body size in a raptor with pronounced reversed sexual size dimorphism: are bigger females better?
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Massemin, Sylvie, Erkki Korpimäki, and Jürgen Wiehn. 2000. Reversed sexual size dimorphism in raptors: evaluation of the hypotheses in kestrels breeding in a temporally changing environment.
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