Just noticed your post. I have been to Port El Kantaoui a number of times but have not done that much birding. There were a number of interesting birds in the farmland on the opposite side of the road from the hotels. I saw Hoopoe, Spotless Starling, Southern Grey Shrike, Laughing Dove and Spanish Sparrow on a few of the walks I did. Port El Kantaoui harbour and beachfront may provide seabirds such as Caspian Tern and Yellow Legged Gull.
I did not do any wetlands but I think there may be some down near Monastir. The organized tours to the Sahara can be good as I saw a House Bunting on the way to the Schott El Jerid, which is a great salt lake down south where Star Wars was filmed.
I would suggest that Djerba is a little too far for you to travel as it is way south, but it depends on what sort of holiday you want.
Hope this is of some help. Enjoy the holiday and let us know what you see.
I went on holiday to the Island of Djerba, Tunisia last September 15th to 28th. I thought it worth sharing the birds seen as it was quite productive. All the main hotels are along a strip of the North East coast and are conveniently situated between two rather good coastal salt-flats, one of which remains as a tidal lagoon known as the Blue Lagoon south of the headland of Rass Taguermes and to the east of the small town Tazdaine and the other the main bay and peninsula off the capital Houmt Souk called Ras Rmal. A number of rather good birds were also seen around the hotel grounds (Iberostar Mehari). The list is as follows:
Greater Flamingo Eurasian Spoonbill Grey Heron Great White Egret Little Egret Common Kestrel Western Marsh Harrier Eurasian Oystercatcher Black Winged Stilt European Golden Plover Grey Plover Common Ringed Plover Kentish Plover Whimbrel Eurasian Curlew Spotted Redshank Common Redshank Common Greenshank Common Sandpiper Ruddy Turnstone Sanderling Curlew Sandpiper Dunlin Audoin's Gull yellow Legged Gull Lesser Black backed Gull Slender Billed Gull Gull Billed Tern Caspian Tern Lesser Crested Tern Sandwich Tern Rock Dove Collared Dove Laughing Dove Little Owl Wryneck Ring Necked Parakeet European Bee Eater Common Hoopoe Southern Grey Shrike Common Raven Barn Swallow Crested Lark Tristram's Warbler Sardinian Warbler Spotless Starling Blackbird Black Redstart Northern Wheatear Black Eared Wheatear Yellow Wagtail Spanish Sparrow
That was 52 species in all and an enjoyable set of early mornings birding. Aim to be finished by 11.00 am as the heat is hard work after. I can recommend the local yellow taxis to get to the sites as they are cheap, helpful and abundant.