In the Netherlands and Belgium we know two types of crows, the carrion crow (Corvus corone) and the hooded crow (Corvus cornix). The black crow is present all year round in the Netherlands and Belgium. The hooded crow is a migrant and winter guest. The Netherlands is located just south of the zone where both species breed together. In the Netherlands, breeding cases of hooded crows or mixed pairs of black and hooded crows have become increasingly rare.
Appearance
The figure and behavior of the hooded crow is the same as that of the black crow. The head, throat and chest, tail and wings, beak and legs are black, while the rest of the body, top and bottom, is gray. It remains a bit curious that a bird with such colors is called fur. The name gray crow would have made more sense since fur is often used for birds that go through life with one or more white feathers through a mutation or deficiency disease. We can see this for example in blackbirds and also black crows that are sometimes adorned with several white feathers.
Less and less hooded crows
There was a time when the hooded crow was a very common winter guest in the Netherlands and Belgium. Jacobus Pieter Thijsse (1865-1945) teacher, conservationist and field biologist, wrote in 1910 in his book ?? Autumn ??: ?? and around the tenth (October) they start to come in all seriousness, by the thousands and thousands at the same time ?? . This was a normal phenomenon when JPThijsse made his many nature observations. However, the many studies show that the number of migrants and hibernators of the hooded crow has decreased very sharply since the 1970s and probably earlier.
In Western Europe, the species is almost entirely absent as a breeding bird. Although the hooded crows do have a winter migration to the south, the hooded crows from Scandinavia have continued to winter more and more north in recent decades, in the south of Norway and Sweden and in Denmark. It is assumed that the Scandinavian birds have hibernated further north as a result of enrichment of the northern European agricultural land and a milder climate, the hooded crow can find sufficient food in the winter within its own breeding area. The few specimens that now hibernate in Belgium and the Netherlands are mainly found in the North of the Netherlands. The decrease in the Netherlands and certainly also in Belgium, which is even more southerly, is undeniable. The hooded crow, especially in the second half of the twentieth century, declined sharply as a migrant and hibernator. The limited presence is very clear from the observations of SOVON, the Foundation for Ornithological Field Research Netherlands. The same phenomenon also occurred in northwestern Germany at the same time. Where previously groups of wandering hooded crows could be observed, it is almost a sensation to observe a solitary specimen.
Relationship hooded and black crow
The hooded crow is considered a subspecies of the black crow. There was a period when the species were also considered as one species. A species is usually understood to mean an animal group that can reproduce and have fertile offspring. On the basis of this definition, there is one species, other definitions mean that there is a subspecies. Geographically, the two species have a different distribution, but overlap each other over a zone of approximately 25 to 160 kilometers width and a length of 2100 kilometers, and within that zone relatively many mixed pairs occur.
Several color phases can be found that are always fertile when backcrossing with the original form. In the crosses it appears that the color of the plumage has very little selection value. It is not clear what stimulates the crows when choosing a partner to choose a partner of their own species or of the subspecies. There are no differences in the behavior of either species. Also in physique, eggs and voice there is no difference between the black and hooded crow.
The emergence of a subspecies usually arises from a long-term separation by geographical barriers such as mountain ranges and seas. The division in the population of black crows may have arisen during the last ice age and in one of the separated populations the hooded crow formed. However, the isolation has not lasted long enough to further develop the species into their own species.
Breeding cases of the hooded crow on the Wadden Islands are not really very special. Huizinga therefore believes that the Dutch Wadden Islands and enclave of the hooded crow is within the distribution area of the black crow. The Wadden Islands are located about 200 kilometers from the nearest continuous distribution area of the hooded crow in Denmark. In view of the developments in recent decades, it is not expected that new breeding birds from the north will still be established in this population. The population will probably continue to consist of black, hooded and hybrid crows that reside as resident birds on the Wadden Islands. Whether this population remains fur will depend on the establishment of new specimens and whether they are black or fur. Time will tell, but it is most likely that the fur from this population will increasingly lose ground and the hooded crow will disappear from our resident birds forever and the hooded crow will also become a rare winter guest.
Reproduction
Both the black and the hooded crow never nest in colonies like the rook, while the crows in autumn and winter do mix in groups with sometimes more than a hundred birds. As a rule, five eggs are laid, sometimes four and also six. The laying of the eggs takes place in the period from March to May. The female incubates the eggs in 17 to 18 days. The first days the male provides the food and after about ten days the female will help with feeding the young. The black and hooded crow are not very fastidious omnivores. The young stay in the nest for about a month and then fledge. By the end of the second year of life, they reach sexual maturity and then look for a mate with whom they will go through life monogamous.