Being spring here in South Africa, many creatures have already been a-courting and are turning to nest building or are in the process of brooding their young.
Last week’s post highlighted the increased activity of Egyptian geese and I mentioned how these geese may harass nesting birds such as black sparrowhawks with a view to evicting them and taking over their nests.
Egyptian geese evicting black sparrowhawks from their nests has been documented by researchers working in the Cape Peninsular. For more information and photographs of geese evicting nesting sparrowhawks and occupying nests see here and here.
Interestingly black sparrowhawks that have experienced being evicted from their nests by Egyptian geese have developed strategies that include building multiple nests and breeding earlier in the season (Foote 2016).
A pair of Egyptian geese. These geese are not in our garden – I photographed them at Nsumo Pan at Mkhuze Game Reserve in KwaZulu-Natal
In previous years black sparrowhawks have nested in a tall eucalyptus tree on the margins of the commercial plantation behind our garden. In some breeding seasons we witnessed something like open warfare between Egyptian geese noisily attacking the nesting pair and the black sparrowhawks fighting back in defence of their nest. In each season the black sparrowhawks managed to prevail and went on to raise their young.
Unfortunately though, the last time the black sparrowhawks used their breeding tree they had other problems in the form of tree felling going on all around them, as documented in an earlier post here.
A female black sparrowhawk photographed in July this year, perching in a nearby eucalyptus tree, which is about 80 m from the nesting tree
Although, as explained in the previous post on sparrowhawks, I managed to intervene to stop their nesting tree from being felled, and the female stayed on to raise one chick, the male disappeared during all the disruption and noise of chainsaws and falling trees, and in subsequent years the nesting tree has not been used, not even by Egyptian geese.
However, each year since then, in mid-winter, a female has arrived and remained a few days, often perching in a nearby tree calling loudly. One year a visiting female even teamed up with a mate and although they commenced nest building they too soon disappeared from the neighbourhood.
Photographed in September 2014, a male black sparrowhawk, a dark morph variant, in a tree in our garden. For reasons unknown to us, he and his mate abandoned their nest building and disappeared from the neighbourhood
But this winter a female appeared again and then two other sparrowhawks were seen flying around, which we guessed were skirmishing males. She picked a mate, and one day I even saw them mating (see video below). The pair remained in the neighbourhood, calling their distinctive ‘teddy bear’ call often and they built a nest in the same nesting tree used years before, but in a higher fork of branches against the main stem, starting from scratch as the old nest had disintegrated.
A still from the video of the pair of black sparrowhawks mating in July this year
All seemed to be going well, and a few weeks ago from a distance I could just make out the shape of a chick in the nest. The chick being pure white and about the size of domestic hen was visible from a distance if it stood up near the edge of the nest, but it was too far for a photograph. When closer it is impossible to see into the nest because of the surrounding foliage and its height from the ground. We often saw the parents coming and going from the nest, and although they were not as vocal as before, we heard them calling from time to time.
The nest, looking like a heap of sticks in forks of branches against the main trunk, is extremely well hidden, being very high in a tall eucalyptus tree and obscured by foliage
A few days after seeing the chick we realised that something was wrong. There was no calling and we no longer saw the parents at all. Peering at the nest from a distance all was quiet.
During the past weeks we never heard or saw Egyptian geese going anywhere near the nesting tree. The only largish bird to approach the nesting tree that we were aware of was an African harrier-hawk (gymnogene) that we heard calling from the tree, but although they hunt nestlings I can find no mention of them taking from nests prey as large as black sparrowhawks. Although African harrier-hawks may make use of nests made by other raptors, including black sparrowhawks, I have not read that they actively evict occupants of a nest that is in use.
The female black sparrowhawk is larger than the male. The weight range for a female is 820–1040 grams, and the smaller male 505–630 grams
So there is no closure to this story. We have not seen or heard black sparrowhawks or African harrier-hawks in the neighbourhood for at least the past two weeks (although they may be there unnoticed by us), nor have we been aware of any human activities that may have interfered with the birds. As so often is the case in nature, much happens that we humans remain oblivious of.
All I can offer you is some video footage of the pair of black sparrowhawks who nested unsuccessfully in our neighbourhood this year. First is the female in her favourite perching tree followed by rather shaky footage of her calling – she was quite far off being about 90 metres away. Next is a clip of the pair mating in the same tree. When I first saw them mating I got the camera and had it ready to capture what seemed to be their final coupling. Lastly are some clips from our trail camera of a black sparrowhawk drinking from a trough of water we keep filled for wildlife outside our garden and on the margins of the plantation.
We decided to provide this water trough as the stream that used to run in the small valley between us and the plantation prior to the advent of the commercial plantation, no longer runs – probably because the fast-growing eucalyptus plantation trees require so much water.
Sources: Black sparrowhawks of the Cape Peninsula. 2011. https://blackspar1.wordpress.com/; Roberts VII Multimedia Birds of Southern Africa: PC Edition. 1997-2016 Southern African Birding. For details go to http://www.sabirding.co.za/roberts7/portal.html; Foote, Christopher. 2016. Hawk vs. goose: How to cope with an unpleasant neighbour. BMC Series Blog. https://blogs.biomedcentral.com/bmcseriesblog/2016/05/09/hawk-vs-goose-cope-unpleasant-neighbour/; Suri, Jessleena . . Raptors as urban adaptors? What can Cape Town’s black sparrowhawks tell us about city-dwelling raptors? British Ornithologists Union. https://www.bou.org.uk/suri-urban-raptors/
Posted by Carol