Jon Loman's research:
The Hooded Crow
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The Hooded crow Corvus cornix
The hooded crow is "too well know to need a presentation".
However, I would like to take this opportunity to motivate the use of
Corvus cornix rather than Corvus corone cornix as
scientific name for the form under study. The grey form, "the hooded crow"
is bordered to the west and to the east by all black crows with which it
hybridizes. As no apparent hybrid inviability, nor non random mating, has been
documented, it seems that the common practice, to assign subspecific
status to the different forms, is well motivated. However, if these conditions
really apply (rather than being the conclusion of possibly imperfect human
studies), it is to me inexplicable that the hybrid zone is narrow and well
delimited. I therefore conclude that undocumented mechanism are in force
and these forms are not fully interbreeding. Thus, the grey form should
be regarded as a full species.
- Territorial system in a crow population.
A major part of my dissertation was based on mapping the the relations
and territories of crows in an area of about 15 sq. km. In this
area most adult crows and all fledglings were given wing
could be identified from a distance. The findings are reported in
publication 15. Basically, young crows do not breed
until they have established
themselves in a territory. This may not happen until they are several
years old. Until then, they spend the spring in smaller flocks. In
winter time flocks are larger and may include territorial birds.
However, in my study area, some territorial birds spent part of the
winter in their territories as well. A territory is acquired in either
of two ways. Some crows mate with widowed territorials, males or
females. Sometimes pairs of young crows may find a "weakness" in the
established territorial system and establish themselves there. When so
happens, they have usually made exploratory visits to the area already
in the previous year. Once established, territories (or mates) are
almost never changed.
- Factors affecting clutch size in a crow population.
I have studied factors affecting clutch size in this crow populations
publication 2 and 7. In one experiment (reported
in publication 10) I manipulated
number of nestlings to asses the optimality of the clutch size. In
another experiment (reported in publication 12
I manipulated number of eggs. This showed that
time constrains may be another important factor for the clutch size.
- Roost as information centres. In a field
experiment (publication 8), I and Staffan Tamm investigated the possibility that the
roosting behaviour of crows (and ravens) could fascilitate the
discovery of rich but ephemeral food sources. Indeed, after the first
discovery (by single or few birds) of such a food source, many more
birds arrived on the next day. This, we think, supported the
"information center hypothesis".
- Other studies. Other crow studies have focused
on nest sites (reports 1 and 5), use of road kills
(report 17), and pheasant egg predation
(reports 3, 11, 14 and 16).
Publications, reports and manuscripts
- 1975. Nest distribution in a population of the hooded crow Corvus corone. Ornis Scand. 6:169-178.
- 1977. Factors affecting clutch and brood size in the crow, Corvus cornix. Oikos 29:294-301.
- 1978. Egg shell dumps and crow Corvus cornix predation on simulated birds' nests. Oikos 30:461-466. With G”rgen G”ransson.
- 1978. A model of population dynamics in territorial animals. Anser suppl. 3:163-166.
- 1979. Nest tree selection and vulnerability to predation among hooded crows Corvus corone cornix. Ibis 121:205-207.
- 1980. Social organization and reproductive ecology in a population of the hooded crow Corvus cornix. Thesis. University of Lund.
- 1980. Reproduction in a population of the hooded crow Corvus corone. Holarctic Ecol. 3:26-35.
- 1980. Do roosts serve as "information centres" for crows and ravens? Am. Nat. 115:285-289. With Staffan Tamm.
- 1980. Habitat distribution and feeding strategies of four south Swedish corvid species during winter. Ekol. Pol. 28:95-109.
- 1980. Brood size optimization and adaption among hooded crows Corvus corone. Ibis 122:494-500.
- 1982. Does shooting of breeding crows influence pheasant production? - An experiment. Trans. Intern. Congr. Game Biol. 14:331-334. With Görgen Göransson.
- 1982. A model of clutch size determination in birds. Oecologia 52:253-257.
- 1984. Breeding success in relation to parent size and experience in a population of the hooded crow. Ornis. Scand. 15:183-187.
- 1984. Predation on brown hare and ring-necked pheasant populations in south Sweden. Holarctic Ecol. 15:300-304. With Sam Erlinge, Bo Frylestam, Görgen Göransson, Göran Högstedt, Olof Liberg, Ingvar Nilsson, Torbjörn von Schantz, and Magnus Sylvén.
- 1985. Social organization in a population of the hooded crow. Ardea 73:61-75.
- 1986. Predation and habitat distribution of pheasant nests: A case of ideal freedistribution. Ardea 74:105-109. With Görgen Göransson.
- Manus. The importance of scavening on roadkills for a predator community. With Görgen Göransson, Göran Jansson, Olof Liberg, Torbjörn v. Schantz, and Magnus Sylvén.