African Sacred Ibis (Threskiornis aethiopicus): Impact of an introduced bird species (To cull or not to cull?)

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Historical Background
“The word Threskiornis comes from two words thrēskeuō ‘to worship’ and ornis ‘bird’. This Ibis was once called ‘Ibis religiosa’ in view of its veneration in ancient Egypt. The British Museum (2014) describes that this Ibis was considered sacred due to its association with the god Thoth (moon god) that represented wisdom and writing. This god was often depicted ‘in the form of a man’s body with the head of the Ibis and was the patron of the educated scribes who were responsible for the administration of Egypt’. HBW 2019 suggests that the ‘long bill of the ibis represented the pens or quills’ with which scribes wrote. The importance of animal mummies as ritual offerings, especially the Sacred Ibis, are illustrated in a research paper by Wasef et al (2016). They state ‘It is estimated that 4 million Sacred Ibis mummies were deposited in dedicated catacombs throughout Egypt, with approximately 10,000 mummies interred each year.’

Mummified African Sacred Ibis (Source: Brooklyn Museum).

Distribution and Spread of an ‘invasive’ species
“African Sacred Ibis distribution is classically sub-Saharan and south Africa, Madagascar and Iraq (south of the Sahara, formerly in Egypt). Its image can be found on the Gambia banknote, underlying its popularity. Over time it has spread to Europe, North America and Asia (Yesou et al 2005, Invasive Species Compendium 2019, HBW 2019). Introduction into the wild in these countries is linked to zoos which often allow these birds to fly freely and move out to form feral populations. In France concerted efforts have been taken to cull thousands of Sacred Ibis (3,000, or half of the population was culled by shooting in 2008).

African Sacred Ibis on Gambia banknote.

Entry into Taiwan Avifauna
“The Sacred Ibis entered the wild in Taiwan more than 35 years ago (before 1984) when a zoo enclosure (aviary) in the north (Hsinchu County) was damaged during a typhoon (Chen et al 2018, Wikipedia 2019). Soon the birds were noted to be breeding and by 1998 it was estimated that there were 200 in the wild. By 2010 they were found on islands off the coast 190 km from Taiwan but adjacent to mainland China (Wikipedia 2019; Note: No reports from China yet on eBird). By 2011 a survey estimated the population at 500-600 birds (China Wild Bird Society 2015). Current estimates by the Chinese Wild Bird Federation are 2,500 to 3,000 birds in the wild (Chen et al 2018). Nest counts from aerial photographs show an increase from 300 in 2016 to 800 in 2018 (Chen et al 2018). Attempts have been made since 2016 to reduce the numbers by egg oiling, removing its eggs, destroying its nests and removing young hatchlings. None of these measures have yet proven to be effective (Charlier 2016, Yang 2016, Chen et al 2018). I attempted a graph of available reports over time and the trend appears to be an exponential increase (assuming accurate reports). However the average yearly growth of populations in France was 21.5% and Netherlands 30.1%, supporting linear trends (Smits et al 2010).

African Sacred Ibis in Dayuan Township, Taoyuan City County, Taiwan, 14th January 2019 (Immature bird in image).
Graph of trend increase in Sacred Ibis in Taiwan.

Are Feral Bird Populations Harmful?
“Over the centuries, birds from one region have been introduced into other regions, at times with unexpected, negative impacts. Reflecting on bird introduction/movements/change over time I can think of a few recent local examples. Java Sparrows (Lonchura oryzivora) have been introduced to my region from caged escapees but after many years are still struggling to establish long-term stable populations. In recent years (since 2012) we have seen Hadada Ibis (Bostrychia hagedash) escape from bird parks in the Klang Valley area and slowly establish breeding sites. We have no idea of their impact as yet but they have spread northwards to my region since late 2017. Birds of course will migrate and establish populations in new countries. Since 2008 (especially since 2013) we have seen increasing numbers (thousands) of Asian Openbills (Anastomus oscitans) come south to Peninsular Malaysia either because conditions up north are inhospitable or the widespread infestation of Golden Apple Snails (Pomacea canaliculata) have provided them the necessary food source. Again there does not, as yet, appear to be competition with local bird life and they serve an important role in getting rid of the invasive Golden Apple Snails that feed on aquatic plants, devastate rice crops, are an important vector for parasites (the nematode Angiostrongyulus cantonensis which is linked to human meningitis) and reduce native biodiversity. Finally there is the relentless northward march of the Javan Mynas (Acridotheres javanicus) from Singapore up the peninsula to Perak; a species well known to displace the local Mynas and possibly even Oriental Magpie Robins (Singapore Bird Group 2015). Although some argue that it is critically endangered in its natural Indonesian habitat and introduction elsewhere may save the species (Lewis 2017). I have no romantic notions of supporting exotic introduced species (often called biopollution) but there is a need to see the balance of supporting species struggling in other areas while we prevent feral populations from harming local species.

Are feral populations of the African Sacred Ibis harmful?
The African Sacred Ibis is not a threatened species. Although, in its native region, populations have significantly declined due to loss of habitat and hunting, however it is still considered not globally threatened (HBW 2019). In Taiwan the bird is considered ‘one of the most invasive animal species in the nation’ (Chen et al 2018). It is claimed to compete for resources with species local to Taiwan like herons and egrets (Charlier 2016, Yang 2016). However it is also noted in Taiwan that ‘environmentalists have yet to find any evidence of it harming the local ecology’ (Chen et al 2018). Yesou et al (2005) notes that in France predation has been observed on Tern eggs and other wetland birds (Cattle Egrets, Mallards, Stilts and Lapwings). In addition they have been seen competing for nest sites with Cattle Egrets and Little Egrets. Yesou et al (2005) goes on to say ‘Although the cases outlined above are believed to have had no serious impact on the populations of the species preyed upon, nature conservation societies are concerned that such predation may increase’. The most comprehensive evaluation of the risk of the Sacred Ibis in non-native regions was carried out by Smits et al (2010). They note that the Sacred Ibis can ‘adapt quickly to new situations, has a high dispersal probability and a large distribution’. Birds lay 2-3 eggs and hatching success is good at 60-80% (Avifauna of Taiwan, 2nd edition states ‘4 chicks per nest’). This means that population growth, in the face of no natural predators, is considerable. Foraging behaviour involves taking a large range of prey: invertebrates, molluscs, fish, frogs, lizards, small mammals, bird eggs, nestlings, carrion, vegetable waste and seeds (HBW 2019). Prey is taken by pecking or probing in mud or soft earth or shallow waters. This large range of food and habitat enable easy spread of this species.

African Sacred Ibis feeding in Dayuan Township, Taoyuan City County, Taiwan, 19th January 2019 (Adult birds in image).

“When discussing the ecological impact of the birds Smits et al (2010) suggests ‘possible predation of colonial birds (especially terns and cormorants) and possible competition for nests with spoonbill and species of heron’. But they do indicate that competition of food and nesting sites with other species is still not settled and needs more study. The economic and social impact are low.

“The issues for Taiwan (and lesson we can also learn) include:
1. Possibility of displacement of local wetland species especially Herons and Egrets. Some damage to vegetation due to nest building and droppings possible.
2. Taiwan’s responsibility to its neighbouring countries – possible spread of the African Sacred Ibis beyond Taiwan to mainland China, Japan, Philippines (Note there are eBird reports from Thailand).
3. Finding a humane eradication or control mechanism is needed.
4. There is the possibility of a well-meaning resistance from animal rights or other citizen groups to any form of culling.

“With the good growth rate (~30%) and rapid increase in population, it would be wise to control the African Sacred Ibis bird population early.”

Dato’ Dr Amar-Singh HSS
Ipoh, Perak, Malaysia
22nd. January 2019

References:
1. The British Museum. 2014. A History of the World: Egyptian Ibis. BBC. Available online: LINK.
2. Sally Wasef, Salima Ikram, Sankar Subramanian, Eske Willerslev, Barbara Holland, David Lambert. 2016. Ancient Egyptian sacred ibis mummies: mitogenomics resolves the history of ancient farming. Sciences Conf.org:isaae2016:89429. Available online: LINK.
3. Matheu E, del Hoyo J, Christie DA, Kirwan GM, Garcia EFJ. 2019. African Sacred Ibis (Threskiornis aethiopicus). Handbook of the Birds of the World Alive. Lynx Edicions, Barcelona. Available online: LINK.
4. Invasive Species Compendium: Threskiornis aethiopicus (Sacred Ibis). 2019. Available online: LINK.
5. Chen Kuan-Pei, William Hetherington. 2018. Sacred ibis nest control ineffective: environmentalist. Mar 21, 2018. Taipei Times. Available online: LINK.
6. From Wikipedia, the free encyclopedia: African Sacred Ibis 2019. Available online: LINK.
7. Yesou P, Clergeau, P. 2005. Sacred Ibis: a new invasive species in Europe. Birding World 18 (12): 517-526. (Available online)
8. Alien invasive bird species. The Republic of China Wild Bird Society. 2015. Available online: LINK.
9. Charlier, Phillip. 2016. The Sacred Ibis Runs Rampant in Taiwan. Taiwan English News. Available online: LINK.
10. Yang Shu-Min, Elizabeth Hsu. 2016. Focus Taiwan. Available online: LINK.
11. Singapore Bird Group. 2015. The Javan Myna – mixed fortunes of a familiar stranger. Available online: LINK.
12. Lewis, Danny. 2017. How Escaped Exotic Pet Birds Could Help Save Threatened Species. Smithsonian Magazine. Available online: LINK.
13. Smits RR, P. van Horssen, J. van der Winden. 2010. A risk analysis of the Sacred Ibis in The Netherlands (Including biology and management options of this invasive species). Bureau Waardenburg bv. Commissioned by: Invasive Alien Species Team, Ministry of Agriculture, Nature and Food Quality. Report nr 10-005. Available online: LINK.
14. Avifauna of Taiwan, 2nd edition. Available online: LINK.

Special Note: I am not able to read all the China Wild Bird Society reports (in Chinese) and have to rely on English references with occasional translations using Google.

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2 Responses

  1. Lee Chiu San

    I cannot comment about the African ibis species, but since this website drew my attention to the matter, I have been observing local mynahs for the last 10 years. And yes, I can state categorically that the Javan Mynah does displace the Common Mynah and the Straits Robin.

    I used to maintain a number of aviaries. Every morning, when feeding the birds, I would give the previous day’s leftovers to wild birds. Common Mynahs were, well, common when I started this practice more than 40 years ago.

    In the last 10 years I have noticed a steady decline in their population, and in the last two years I have hardly seen any – perhaps one every three or four months. But there are hordes of Javan Mynahs.

    When the two species were still present in about equal numbers, I noticed that the Javan was more bold, and willing to come closer to humans to take food. In fact, it was not difficult to get wild birds to come to the hand for mealworms.

    The Common Mynah on the other hand, is more circumspect. However, when food was tossed to the birds, I found that Common Mynahs could hold their own and even fight off their Javan cousins.

    As for Magpie Robins, their population in Singapore has declined tremendously. Whether this is due to poaching, habitat change, or competition from various Mynahs, I cannot say specifically.

    But I do know that Magpie Robins are birds that frequent large suburban gardens and feed off grasshoppers. Both are extremely rare in Singapore today. 50 years ago I could sweep a butterfly net over expanses of grass and collect enough insects to feed my birds. Due to extensive chemical fogging today, any kind of insect is rare, even in my garden, which has been specifically set up with plants to attract them. The Robins could simply have starved to death.

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    • Thanks Lee CS for that response. Regarding the insect life in gardens: my wife and I maintain a wild urban garden with a compost heap and use no insecticide. Yet the insect population has declined markedly, especially these past 3-5 years. Probably a global phenomena linked to man’s destruction & pollution of the environment by everyday activities that have reached a tipping point.
      Amar

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