Saturday 23 May 2015

First Sunt Forest visit for a while

I haven't visited the Sunt Forest for a while, so I made a visit today with Marwa and her sister Safaa. The White Nile is rising and starting to flood some of the fields, making it good for waterbirds. We took a boat our to Um Shegira, the long thin island about 100m out, which was a first time for me (though known as a former birding and ringing site of local birder Esmat). The big surprise for me was the large number of African Swamphens feeding out on the open mud, with 66 counted from the shore and another 59 on Um Shegira, and both numbers being highly conservative. Previously known by only one published record, Marwa and I have found them to be common at local sewage sites, but I never expected to see numbers like these. I have visited this site 7 times previously, though never at this time of year, and never seen them before.

African Swamphens, Sunt Forest 22nd May 2015

Marwa has seen African Jacanas here before and several others have seen them in the area around Khartoum and published about them on this blog, but this was the first time I have ever seen them in Sudan. Again, they were quite common. There were quite a lot of storks around, including a few Abdim's and Yellow-billed, plus hundreds of African Openbills. The arrival of these species often signal the start of the rains. There were a number of other interesting waterbirds around, including some migrants still present.

African Jacanas, Sunt Forest 22nd May 2015

Pink-backed Pelican, Sunt Forest 22nd May 2015

African Openbill, Sunt Forest 22nd May 2015

Black-crowned Night Herons, Sunt Forest 22nd May 2015

Sacred Ibises, Sunt Forest 22nd May 2015

Great White Pelicans, Sunt Forest 22nd May 2015

Spur-winged Geese, Sunt Forest 22nd May 2015

Grivett Monkey, Sunt Forest 22nd May 2015

Unfortunately this will probably be my last visit here. I wish I had taken the boat out to Um Shegira more often. It only cost 100 SDG for the three of us to take a short 15 to 20 min trip along the length of the island.

Wednesday 20 May 2015

The amazing variation of weaver eggs

I have been doing little general birding recently, hence the lack of posts. The reason is that I am trying to finish off my study of Cinnamon and Northern Masked Weavers before I leave Sudan in early June. I have been trying to get some more information about nesting, so, wearing my chest waders, I have been wading through sewage at Bahri to check nests and take measurements. As with the Cinnamon Weavers I've been studying in Sennar, I have been struck by the incredible variation of the eggs. Generally birds show little egg variation within a single species, but many weavers (possibly all, but I do not know) show huge variation, with different background coloration, different levels of spotting and different colours of the spots. A selection is shown below.

Cinnamon Weaver eggs, Sennar, Sudan

Northern Masked Weaver eggs, Bahri, Sudan

These two species have almost never been studied before, but one of the few studies was by Wendy Jackson, who investigated the reasons for this egg variation by studying Northern Masked Weavers in northern Kenya. She tested the hypothesis that this is a defence against brood parasitism, a behaviour more commonly known from groups such as cuckoos and cowbirds. The big difference here is that weavers are not looking to lay their eggs in the nest of another species, but simply to offload eggs into the nests of other weavers to increase their own chances of raising more young. It seems that the small woven nests of weavers limit the number of eggs that can be laid to 3, so any additional eggs above this number are best laid in a nest nearby. By having such variation in eggs the birds are better able to spot when an egg is from a neighbour and remove it. There are actually many species that are known to do brood parasitism in this way, such as the Common Starling, but few have evolved such variation in egg design as a way to combat it.