Wednesday, December 30, 2009

Dashing and Endangered - Saddle-billed Stork



Adult male Saddle-billed Stork walking along a water course in Moremi, Botswana

Possibly one of the most striking birds occurring along the rivers and wetlands of sub-Saharan Africa is the Saddle-billed Stork Ephippiorhynchus senegalensis. In South Africa, this species is classified as “Endangered” and the population estimate for the species 10 years ago was less than 150 individuals. Most of these birds occur in the Kruger National Park with a handful of birds still being recorded in northern Zululand as far south as Lake St Lucia within the Isimangaliso Wetland Park (Barnes, 2000). Further north on the continent it is also never common as it is not a gregarious bird like other most other storks are and its territoriality limits the number of birds that can occur, even in large areas of suitable habitat.



Suitable habitat for this species consists of aquatic habitats in open country, where they favour large rivers, freshwater wetlands and floodplains. In Kruger these birds are found along the large river systems and a few large man-made water reservoirs for most of the year, but in years of good rainfall, are quick to exploit the numerous seasonal pans and seeps that form in many areas and where a host of aquatic prey species abound under these temporarily favourable conditions. As mentioned, they feed mostly on aquatic animals and are capable fishermen that can take fish-prey up to 2kg!


Unlike most other southern African stork species, it is fairly easy to separate the male from the female of a pair in the field. Adult females have a bright yellow eye while males have a dark red eye and two yellow wattles at the base of the bill. It is also possible to identify individual birds from each other by looking at the pattern on the bill where the red and black meet. This seems to be unique in each bird, similar to fingerprints in humans. One does however need to get really close to the birds to be able to do this.






























Two male Saddle-billed Storks from the Kruger National Park clearly showing the unique patterning on their bills that facilitates individual identification of birds. The bird on the lft is one of a pair found near Manzinhlophe during the survey while the bird on the right was located on the Mbiyamiti two weeks later. No pair could be found at Mbiyamiti during the survey.

It is this technique which forms an important component of our population study of this species in the Kruger National Park, run by Marcelle van den Hoven, a BTech-student from the Tshwane University of Technology. The study will run from October 2009 – September 2010 and visitors to the Park are encouraged to assist in this study by contributing images and details of sightings of these birds to the database. Feedback and details of sightings can be e-mailed to storks@ewt.org.za




Copy of the flier that is available for information of visitors wishing to contribute to the survey. The initial response has been excellent.


The initial response from the public has been very good and a lot of data on sightings have been received, some with really good quality images that will assist in identifying individual birds. We also conducted a survey of the southern half of the Kruger National Park during early December 2009 using 5 teams of observers that covered over 3000km over the 3 days of the survey. Due to excessive rain in the area in the preceding 2 weeks, a multitude of little pans had formed in the veld making observations very difficult and initial results were rather poor due to the fact that the birds abandoned their usual haunts along the major rivers and were now concentrating their foraging on these pans. This made them rather tricky to find!


An interesting development regarding the survey was an e-mail sent to the SABirdNet by a Canadian birder that visited the Kruger Park during October 2009. He had seen pairs of Saddle-billed Storks on 4 occasions during his 3-day visit and had sent the information to the database. However, he questioned the accuracy of the figures of the population status of the species quoted on the posters and pamphlets of the survey that have been put up across the Park and are available at most reception areas, gates and shops. According to his calculations, that took into account the entire size of the Park and the road network that traverses it, he estimated that the population in Kruger alone should exceed 4000 birds! To add insult to wild assumption, he also accused the Project and the parties involved in it of dishonesty and blowing the status of the species out of proportion to suit their own needs.


After my initial reply to the individual quoting the Red Data Book of Birds of South Africa, Lesotho and Swaziland (Barnes, 2000) confirming the status and underlining the low density of this species throughout its range, I received a direct reply from the individual concerned that indicated his refusal to accept this and expanding on his theory that the species is far more numerous than what is believed. This was my second reply to the individual concerned:


“Dear XXX


Thanks for the reply.


I would be very interested to hear on what factual information you base your suggestion that there could be 4000+ individual SBS in Kruger. It is very difficult to base population estimates on a very small number of sightings from a limited number of individuals and on the incorrect assumption that the entire Kruger provides suitable habitat for this species. Hence our project which aims to obtain more extensive records on this species and ideally would like to reach a point where we can individually identify birds in the population. Considering that the majority of tourist routes in Kruger were developed in proximity to the river systems and larger drainage lines which could potentially provide habitat for this species, there could also be considerable bias towards the likelihood of seeing this species.


Please keep in mind that the population of SBS in Kruger and elsewhere is influenced by a range of factors which severely limits their distribution to a fraction of the entire Park, namely:


• Although this species occurs widely throughout sub-Saharan Africa (apart from the arid south-west), it is nowhere considered to be numerous.
• Even in extensive suitable habitat, its territoriality and solitary nesting habits contribute to the fact that they are nowhere abundant. They are very different to most other storks species due to the fact that they are not gregarious and sightings of more than 2 birds together are very likely that of a pair with their offspring.
• Available habitat in Kruger is restricted to riverine areas. Seasonal pans and seeps are only accessible in years of sufficient rainfall and does not provide suitable foraging areas throughout the year.
• The seasonal nature of the flow of most of the smaller rivers and streams in Kruger severely limits the accessible habitat for this species. This is especially important when it should be considered that such systems will need to function as foraging areas during the breeding season which mostly occurs during the dry season in Kruger when the demand for food with this species would possible be highest.
• Several of the larger rivers are also not flowing throughout the year anymore due to a number of factors, mostly induced by human activities further up-stream. This further reduces suitable habitat and feeding opportunities for breeding birds in this area. For example, one of the major rivers in the Park is the Olifants. Our annual surveys (2006-2009) of fish-eating birds along the 92kms of this river that runs through Kruger shows that there are at most 3 pairs that occur along it.
• If you extrapolate this figure to the available suitable habitat in Kruger, it is highly unlikely that you will get to the figure you have quoted.
• Alan Kemp and his team conducted an aerial census of the entire Kruger in 1993 that revealed a total of 40 adults and 17 juveniles and sub-adults (like the bird in your photograph). That’s a little less than 2% of your estimate. We do plan to repeat this census this coming dry season and, hopefully, for a number of years to come. Will keep you posted on results.
• Subsequent records and surveys have revealed at total of 20 active nesting sites of this species in Kruger in 1993 (Benn et al, 1995). We are hoping to acquire more current data in this regard during the coming months, but it is unlikely that there would have been a marked increase in the number of breeding sites in the Park, especially if you consider the current ecological status of rivers in the Kruger.


Based on the above, the estimate of a 100 individuals in Kruger is probably optimistic.


There are several references available to support the above, but I suggest that you work through the texts of the following for a start:


• Hancock, J.A., Kushlan, J.A. & Kahl, M.P. 1992, Storks, Ibises and Spoonbills of the World. Academic Press.
• Barnes, K.N. (ed.) 2000. The Eskom Red Data Book of Birds of South Africa, Lesotho and Swaziland. BirdLife SA/ADU.
• Hockey, P.A.R., Dear W.R.J. & Ryan, P.G. (eds.) 2005. Roberts Birds of Southern Africa. 7th edition. John Voelcker Bird Book Fund.
• Renshaw, E. 1993. Modelling Biological Populations in Space and Time. Cambridge University Press.


Please let me know if you have any further queries on this matter.


Regards
AndrĂ© Botha”


Unfortunately, this misconception is not uncommon with species such as the Saddle-billed Stork and several more of the birds that we work with. Even experienced birders are sometimes lured into to the illusion that some species are more common than what they in reality are. Rarity and scale of threat cannot be attributed to a species based on a handful of sightings or the ease with which it is found.


An excellent example of this is the Taita Falcon Falco fasciinucha. Most birders in South Africa know that a pair of these birds breed just west of the Strijdom-tunnel on the way to the Lowveld, a site looked after by one of the BirdLife-trained guides, Michael Kumako. On most days, it is possible to have good views of these birds within about 30 minutes of your arrival and most birders that have visited this part of Africa and ticked this species off their lists, probably saw them here. What people don’t realize however is that this is one of only 7 breeding pairs of this bird in the country and that they are nowhere common throughout their very scattered range in Africa. In fact, this is easily the rarest of all breeding birds in South Africa!




Taita Falcon - one of the rarest breeding birds in South Africa
(Photo: Ron Hartley)

Further details on the activities and findings of the Saddle-billed Stork Survey of the Kruger National Park will be provided in due course.

3 comments:

  1. Wow, the Saddle billed Stork is an awesome looking bird. Great photos and post.

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  3. what a beautiful Saddle billed stork! I love those pictures, they reminded me of the great bird photo album by Sildenafil Citrate the Russian bird expert!

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