Recently, St Nicholas Convent celebrated their 75th anniversary. Naturally, this called for a celebration. Preparations were painstakingly made. Part of the preparations involved getting 2 beautiful white doves to be released at the celebrations. With the entire school population gathered (both primary and secondary school), the cage of the two white doves was opened with much trepidation.
Imagine the horror when upon release, the doves were immediately attacked by 2 house crows (Corvus splendens)!
Source: The Amateur Birder’s Journal, Stories & Photographs by JRCompton
(Picture provided for visual effect. Bird attacked in the picture is a Juvenile Hawk)
As all the action was taking place high in the sky, the teachers were unable to intervene and the entire school population watched as one poor dove got caught and tried to fight back. To the cheers of the school’s population, it managed to escape for a bit… only to get caught again. The crows carried it to a nearby roof to continue working on their prize. This time, the dove’s efforts to fight back proved to be futile and, in front of the assembly, the dove went still and the crows flew off with it, leaving a rather shocked school assembly.
In the end, the other white dove fell into a drain and was rescued by teachers. The students then had to write a story on the incident and how it affected them. Lol!
This incident was related to me by my younger sister who had been present at that assembly. While she was more interested in the symbolism (plaintively wailing “Those birds were supposed to represent my school!”), I was curious as to why would the crows think about attacking another bird.
I often hear about birds attacking people and other animals but why do they attack other birds? All along, I have had the impression that birds live together in harmony… bickering only over food like siblings (and I blame Disney for this!).
Crow Attacks on other Birds
Intrigued, I went to scour the net for any such stories. To my surprise, there are many accounts of birds attacking other birds! Most sightings have been mentioned in forums and blogs.
Examples found include:
- IslamOnline.Net “Symbolism? The Young Dove, The Black Crow and the Storm” http://www.islamonline.net/discussione/thread.jspa;jsessionid=HhvFBLvLnP384Jtfv0tLh1wBwZYySvsp9PGnp1G1JkRDQZTTS5jl!-1763432234?messageID=2392क़
- Bird Ecology Study Group “Mobbing of Spotted Wood Owl at Toa Payoh” http://besgroup.talfrynature.com/2008/01/27/mobbing-of-spotted-wood-owl-at-toa-payoh/
- Bird Ecology Study Group “Nesting of Spotted Dove” http://besgroup.talfrynature.com/category/doves/
Possible Reasons of Crow Attacks on Other Birds
Among the many explanations offered up, self-preservation, removal of a threat to their young and food are the more accepted explanations.
i) Mobbing:
Mobbing occurs when a bird or many birds start attacking another bird by making repeated dives and loud calls to disturb it. They may or may not strike the targets of the mobbing. Often, the birds on the receiving end of the mobbing are birds of prey, buzzards, hawks and owls in particular. Owls and Hawks are the crow’s largest predators. While it might seem stupid (or should I say bird-brained? Heh) for the crows to disturb the very birds who could and would eat them, mobbing behaviour is a defence response to a perceived threat from a predatory bird. This typical anti-predator behaviour is to keep predator birds out of the crow’s territory (The crow is known to be an aggressive bird which is fiercely territorial).
Source: Flickr “Mobbing a redtailed hawk” by wolfpix.
Several eyewitnesses to mobbing incidents by crows have detailed their stories.
a) Rojak Librarian “Collared Scoop owl ‘captured’ in the afternoon” http://mymindisrojak.blogspot.com/2006/06/collared-scoop-owl-captured-in.html
b) Bird Ecology Study Group “Mobbing of Spotted Wood Owl at Toa Payoh” http://besgroup.talfrynature.com/2008/01/27/mobbing-of-spotted-wood-owl-at-toa-payoh/
The targets of the mobbing behaviour in the blogs’ accounts are owls. Owls are popular targets, especially when caught resting during the daytime. It is possible that the mobbing birds know that it is safe to mob owls as these nocturnal birds are unable to attack the constantly moving mobbing birds. Fret not for the owls. Mobbing rarely escalates into physical confrontation which could be damaging to all birds involved. As seen from the eyewitness accounts, most birds on the receiving end of a group mobbing will either sit it out (by ignoring them) or make a hasty retreat.
Source: Flickr ““unfazed2” by akryszkiewicz
While the crow family is perhaps the most well known for its mobbing behaviour, it is not limited to crows. As in the stories, mobbing usually involves more than one bird in pursuit. Any species of the bird can join in with the mobbing of birds which are potential predators. Mobbing birds may include songbirds, crows, woodpeckers and those as small as hummingbirds. Symbolism? The Young Dove, The Black Crow and the Storm” (found in http://www.islamonline.net/discussione/thread.jspa;jsessionid=HhvFBLvLnP384Jtfv0tLh1wBwZYySvsp9PGnp1G1JkRDQZTTS5jl!-1763432234?messageID=2392क़) is one such account of how different bird species came together to chase off a predator. A crow was attacking a young dove when a human and other birds came to intervene. While reading this story, i was struck by how similar this incident was to the bull incident in the youtube video Prof Sivasothi had shown us in the last lecture.
It really does change one's perspective. To an onlooker, the flock of birds attacking one lone bird may seem unfair and even cruel. But, knowledge that the bird on the receiving end is a predator of the very birds attacking it and that the attacking birds might one day lose their life to the victim of the mobbing shows how matters are not always what they seem.
Why do birds mob predators? Many answers have been readily offered. Besides uniting to chase off potential threats to the community, it could be to alert others of the presence of the predator birds, educate young birds on the identity of their enemies or protect their young from potential threats.
ii) For food:
The crows attacking the doves in the introduction story were of course attacking the young doves for food purposes. It was just amusing to imagine how the jaws of the entire school population dropped at the same time. Lol!
Kidding aside, the omnivorous crow is not just interested in food scraps. It is known to attack and kill indigenous birds to eat, or to get to, their eggs. Two blog posts bear eyewitness accounts as to how crows attack the nests.
a) Bird Ecology Study “Nesting of Spotted Dove” http://besgroup.talfrynature.com/category/doves/
The crows were trying to attack the nest in order to eat the eggs in the
Spotted Dove’s nest. Human intervention saved the eggs.
b) Bird Ecology Study “Attack on the Black-shouldered Kite’s nest” http://besgroup.talfrynature.com/category/crows/
Crows were successful in raiding the nest located in Lim Chu Kang cemetery area.
Down with the Crow?
Does this give us a stronger argument to cull Crows? Not necessarily. A number of studies have concluded that removing crows will make no change in the end result (that of most of the young birds/eggs being eaten). The removal of crows does not increase nest success of survival of the bird to be protected. This is because nearly always some other predator steps up to eat the same number of eggs and young birds, or they die for other reasons.
This idea is called compensatory mortality in which nature manages to strike a balance. (It is interesting to note how similar compensatory mortality and the bee example in the last lecture are in how nature balances its proportion.)
Compensatory mortality can be better explained with the analogy of handicapped parking spaces at the shopping centre. Kevin McGowan did a great job of explaining it.
“ You drive up to the mall, looking for a parking space in a crowded lot. You can't find a parking space, but there are four near the entrance that are reserved for handicapped permits only. You complain and think that if only those handicapped restrictions weren't there, you could park in those spots (common sense). In truth, of course, if those spaces were not reserved they would have been taken long ago, just like all the other spaces in the lot.
So if one more egg hatches, that will be one more nestling that gets eaten by a raccoon. Or if one more nestling makes it out of the nest, that's one more fledging for another predator to eat. Or, if one more young bird survives to fly to South America, that's one more bird that falls into the ocean during the bad storm (1001dying instead of 1000). And so on and so on. This concept of compensatory mortality is vital to the idea of game management. What it says to the managers is that it doesn't matter to the population if hunters take a bunch of young that were slated to die anyway. If you keep your take within the limits of the mortality that normally occurs, exactly NOTHING happens to the overall population, even if you kill a million individuals (like the million Mallards that are killed in the US every year). And it works! Of course, if you exceed the normal mortality things go awry. Or if the sources of mortality increase in an unusual way (huge losses in habitat, for instance, or total loss of food supply at a staging ground) then bad things happen. But the normal fluctuations of a stable community just absorb the small perturbations.
So, although you might see a crow eating a baby robin, that is not bad. MOST baby robins die before reaching adulthood. That's why the robins nest so many times during the summer. The presence of crows in an area will not mean all the robins and cardinals will disappear.“
In other words? The doves released at the school may have been eaten by another predator if the crows had not gotten to it first. Not much consolation to the many witnesses of the school’s incident, but here’s hoping that this blog post helps to vindicate the crow a little!
References:
Bird Ecology Study Group “Crows Archive”
http://besgroup.talfrynature.com/category/crows/
Frequently asked questions about crows by Dr Kevin J. McGowan , Cornell University “Since the crows came we don’t have any little birds around anymore!” http://www.birds.cornell.edu/crows/crowfaq.htm#compens
Removal Studies "Studies investigating the removal of crows as an aid to reproductive success in other birds." http://www.birds.cornell.edu/crows/removal.htm
The RSPB Advice: Ask an Expert “Why would a crow attack a buzzard in flight? – I would’ve thought the buzzard to be more powerful of the two birds?” http://www.rspb.org.uk/advice/expert/previous/mobbing.asp