I wrote to the Section Ranger at MZNP with your initial post. Herewith her reply:
Please reply to this lady thanking her for her enquiry.
We unfortunately do not have a large colony of red bishop birds in Mountain Zebra National Park, although we do see a few individuals during breeding season in one of the reeded river crossings along Kranskop loop.
We don’t have records of sightings as early as July (as it’s still too much in the deep of winter).
I suggest, if you are capable, to visit Addo Elephant National Park. Although their temperatures don’t reach as cold as MZNP, they do have a very large colony and a superb bird hide in which to view the birds.
Their breeding season (in summer-rainfall areas as is the Eastern Cape) are September to March, which is the best time to view them in large colonies in their breeding plumage and, of course, courting and nesting.
Lastly, there is quite a lot of information on the internet (as well as links to research papers), which may assist you with the information you require regarding thermal tolerances.
I hope this assists with your enquiry. Please let me know if it is not suitable for you to visit AENP (or it’s too far a field) so that I can find out more about breeding colonies in this (Cradock) area, however I strongly suggest AENP for excellent viewing opportunities.
Robyn Woods (Miss)
Senior Section Ranger
South African National Parks (Pty) Ltd
Mountain Zebra National Park
It might be an idea for you to email Robyn directly yourself - if you would like to do this, please PM me.