Hello everyone. First time forum user here. Just wondering if there is only 1 pair of swamp harriers per wetland/swamp/lake system. If so, where do the offspring go to make their mark on the world?
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Welcome to the forum digbyboel,
I would say, it depends on the food supply, if there is enough to sustain a larger population of any kind, they will tolerate more birds. I don’t know a lot about the Swamp Harrier, but some months ago I counted about 20 Black-shouldered Kites in wetlands I often go to, there were mice in abundance. Unfortunately humans create those problems for birds , and most other animals in the wild, by destroying their habitat, we deprive them of food and living space. What happens to the birds that can’t find their own territory? No habitat, no food, no breeding, no life…… Anyway, sorry to sound pessimistic, there are many people around trying their best to change the grim outlook .
M-L
Welcome to the forum, Digby.
Interesting question. I presume you've only ever observed a maximum of two swamp harriers in the swamps you've visited. I've observed swamp harriers on the edge of Lake Alexandrina in SA & I can't recall seeing more than two at a time. I imagine that numbers would depend on the size of the swamp & its natural qualities such as food & nesting resources & lack of unnatural disturbances resources such as jet skis, grazing cattle & toxins. Given the vandalism of so many wetlands by developers it must surely be increasingly difficult for young swamp harriers to find new areas to colonise.
I'd be interested to learn of your thoughts on this, Digby.
Thanks Woko,
I appreciate your thoughts. I live just by Lake Joondalup which is north of Perth and have visited many of the other swamps and wetlands in and around Perth (eg Herdsman Lake, Lake Claremont, Moore River, Bibra Lake) and always only see a single pair of swamp harriers. As they have a clutch size of 3-4, I thought there might be more of them around, especially considering the size of Lake Joondalup and its abundance of prey. Unfortunately I don't know the survival rate of swamp harrier chicks but I assume that because they nest on the ground on a trampled reed platform then they are more prone to feral animal attacks (cats/foxes). The breeding adults also will abandon the nest at any threat or approach from intruders, leaving their chicks vulnerable. But in saying that, the nest is usually in dense extensive reed beds making access difficult. Perhaps the swamp harriers just keep reproducing in the hope that their offspring will fly off and find a lake/swamp with recently deceased senior swamp harriers. The fact that there are always a pair of swamp harriers in all these places may suggest this. I just keep wondering if juvenile swamp harriers compete for regions or simply don't have the resources to survive with other swamp harriers. Sorry if I am going on a bit, but a part of me really worries about these raptors and I am hoping I have nothing to worry about.
Regards,
Digby
Hello Araminta,
Thank you for your thoughts. Yes it is shame that the wetlands are a habitat that us humans so often transform into suburbia.
Regards,
Digby
Hi Digby. To a considerable extent I suppose that what applies to young Swamp Harriers seeking new territories could apply to many bird species. E.g., I often wonder what happens to all the New Holland Honeyeater young at our place. Our population on 17.5 revegetated hectares seems to have stablised at about 30. There are other properties nearby which would take some as the revegetation projects there mature. Whether the increase in habitat is sufficient to cater for all the young New Holland Honeyeaters produced here is an interesting question.
In the case of Swamp Harriers, natural & unnatural losses would account for some of the young. Perhaps only enough young survive to replace or partially replace dead adults. Given the depletion in wetlands it's a grim picture for many young Swamp Harriers, at least theoretically.
I understand that in the UK their Marsh Harriers are increasingly nesting in fields. Whether this is happening in Australia I don't know but I guess it's possible that the Australian Swamp Harrier might adapt to this environment. If so, there may be a movement of Swamp Harrier young into drier country. All good stuff for research if it hasn't been done already.
On the subject of numbers (you wrote that you've only ever seen one pair in a swamp), the Readers Digest Book of Australian Bird says that "Swamp harriers are usually seen alone or in pairs, though groups may congregate where food is abundant. But even then they do not behave as a flock."