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Name: Vida
Location: N/A
Country: N/A
Date: N/A 


Question:
I live near a 17 acre lake. We had a pair of nesting mutes which had successfully raised 6 surviving cygnets each summer for three summers.
This year, two trumpeters flew in and the mute male fought them to the death. His efforts were complicated by the fact that wire had been placed in the water to keep the geese and ducks from walking onto the shore. The mute male died from his attack of the trumpeter and being tangled in the wire.
The female mute remained on her nest and successfully hatched 7 cygnets! We were all so happy to see her doing such a great job!
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The cygnets are not quite full grown now. They are still dark grey and their wings are still small. For some reason, the mother has begun 'rejecting' one of the cygnets. She has gone so far a crying cygnet into the weeds away from the other 6. She had been raising the 7 toghether all along and I don't have any idea why she would 'turn' on this one.

Her attack on it this morning was quite violent. It must have returned to the group during the night. At day light, she drove it away by trying to drown it with her head, and then with her body. It scrambled onto shore and tried to escape her.

Do you have any idea why she might do this? I'm thinking perhaps she thinks she should only have 6? She is alone raising them, perhaps he wasn't 'behaving'. Or, perhaps it's too small help this poor cygnet.



Replies:
I have been trying for some days to figure out how to respond to this message. First of all, it is almost certain that the mute swan did NOT die from fighting the trumpeter, such fights are almost never fatal. Wire in the water? That seems an incredible hazard for all birds and wildlife; without knowing details it seems that would be a much more likely cause of death.

As for the aggression of female to young, I haven't found any references yet that help. It is most unlikely the adult can count; there is very little evidence that birds have that capacity, certainly not swans. I really can't think of any reason she would turn on one cygnet. Sometimes parents abandon young that can't keep up, etc. but there really wouldn't be any reason to attack. Are you quite sure this is one of her cygnets?

One of the problems I've had responding is my bias - as a naturalist I would favor a native trumpeter swan over a non-native mute any day. The whole situation: an ecosystem with a high level of human disturbance and modification, and non-native species, makes me a bit sad: where can the trumpeter swans go in such a system?

But I'm sorry I can't answer the question. If I find out anything else I will send it along.

John Elliott



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