The case for the BLACK STILT

Forest and Bird, Volume 18, Issue 3, 1 August 1987, Page 14

The case for the BLACK STILT

Christine

Reed,

In the November 1986 issue of Forest & Bird Conservation Department scientist Dr Murray Williams put forward some personal views on native bird management. It included comments on the black stilt programme in the Mackenzie Basin, questioning the value of the programme in light of the fact that black stilt

~ are naturally hvybridising with the self-introduced pied stilt. Conservation Officer (Aviculture),

who is working on the black stilt, here replies to Murray Williams’ arguments.

| Diedoey: species generate public support and finance for wildlife conservation in general. However there are other side benefits of endangered species research and management. Often it is on the basis that areas are of critical value to an endangered species that it is set aside for conservation, benefitting all wildlife. The application by the Wildlife Service for conservation of the Ahuriri River was a case weighted strongly on the dependence of black stilts on this river. At the time of application, 50 percent of all black stilt breeding pairs were nesting on the river. However, other species will now benefit: wrybill, banded dotterel, blackfronted tern and black-backed gulls. The two predator exclosures erected by the Forest and Bird Society around black stilt nesting areas near Lake Tekapo also benefit scaup, shoveler, paradise shelduck, marsh crake, grey teal and other waterfowl. Similarly the eradiction of cats on Little Barrier Island has long term consequences not only for kakapo and stitchbirds, but also the assemblage of other birds on the island. Internationally, the establishment of

reserves in India for the tiger benefitted this species as well as leopards, the rare swamp deer, and nilgai (blue bull). In this case, an individual species approach was necessary for the greater impact that could be made on decision making. To have taken a community approach to this conservation problem would not have been successful. Attention needed to be drawn to a critical need for conservation before anything was achieved. Research on endangered species-related problems has wider implications for whole communities. A two year study of predator ecology, movements and population dynamics within the Mackenzie Basin has provided information for black stilt management and has implications for the wider sphere of community conservation (R. Pierce, pers.comm.). We are fortunate in New Zealand to have access to a productive valuable pool of researchers, through our six universities. Graduate students should continue to be encouraged to conduct conservation orientated research and avoid a wholly scientific, purely theoretical approach to research.

The "Black stilt Dilemma"

In the face of major predator problems, | would agree with Williams that management of an endangered species on the mainland can only be achieved through long-term population maintenance. We may never be able to leave an endangered species to its own devices on the mainland, unless effective long-term predator control methods are devised while habitat protection continues. This may be impossible for some, if not all mainland endangered species such as the black stilt. At present there are few options open to managers since we are only now beginning to understand predator ecology and control. For this species at least, maintenance of the population on the mainland is the only option until an alternative such as an island situation can be appraised. Management of black stilts for conservation has come under particular criticism from not only Williams but from some scientific staff of the Conservation Department and universities. As Williams points out, hybridisation between black and pied stilts is a problem of much concern. However, he offers a simplistic view of what he terms the "black stilt dilemma’’, that is that black stilts are being genetically swamped by pied stilts through a natural process. Firstly, hybridisation cannot be proclaimed a completely ‘‘natural process’ in the black stilt context, as it is an after fact of a declining population brought about through human alteration of the natural environment. Black stilts evolved in the absence of mammalian predators within a relatively little modified system. With the introduction of ferrets, cats and stoats, black stilts declined dramatically. They have less effective behavioural displays for coping with predation pressure than do their global relatives. Their distraction displays are not very effective against aggressive ground predators. Black stilts are specialists in their feeding

and nesting requirements. They are unique in the Family Recurvirostridae (stilts and avocets) in their preference for braided river systems where they nest as solitary pairs on mid-channel islands. Chicks are reared along the invertebrate-filled side-channels of the riverbed. Destruction of riverbed channels through damming for hydro-elec-tricity generation, creation of artificial channels, diversion of water and water abstraction, together with the drainage of wetlands has forced some birds to nest in more marginal areas where there is less food for chicks and a higher risk of predation (Pierce 1982). The average black stilt fledgling will die before it becomes a productive breeder (Pierce 1986). While black stilts have declined, opportunistic pied stilts have taken advantage of modified habitats and have expanded in number and range since the mid-1850s. In part, success of pied stilts in contrast to poorer survival of blacks can be attributed to their colonial nesting habits, shorter fledgling period, more effective distraction displays and later more synchronised nesting at a time when predation risk is lower (Pierce 1986). There are then, considerable ecological, behavioural and morphological differences between the two species. Hybridisation is partly a result of reproductive compatibility with the pied stilt, since the two species were probably not geographically separated long enough to evolve complete behavioural or ecological barriers to interspecies reproduction. It has been promoted by low black stilt numbers and an imbalance in the sex ratio, biased toward males. Male black stilts tend to take hybrid or pied mates if no other black is available. This mate choice is not random as Williams would suggest. Pierce (1982) experimentally demonstrated positive assortitive mating in black stilts. That is, they tend to choose the darkest plumaged mate available.

Environmental pressures

The parallel drawn by Williams between hybridisation of stilts and that of grey and mallard ducks does not take into account the environmental pressures being exerted in each case. Where black stilt hybridisation can be attributed to low population numbers spread over a million hectares, the duck dilemma has arisen through encroachment of grey duck habitat by the more aggressive successful mallard, a less well defined species discrimination in mate choice and the phenomenon of rape as a sexual strategy in mallards. Perhaps a separate case can be made for conservation of both black stilts and grey ducks, but the type of mangement involved in each case will differ. If one takes the extreme view of what constitutes a species, perhaps we should discount black stilts as such by pure virtue of the fact that they hybridise with a different taxa. Taking a less extreme view, evidence for obvious morphological, ecological and behavioural differences between pied and black stilts, in conjunction with positive assortitive mating led Pierce (1982) to conclude that black stilts should "retain their full specific status’’. This then draws attention to the question

put by Williams of what is worth saving. Where on the continuum of species, subspecies and colour morph do we draw the line of conservation? I suggest that endemic forms having evolved within and being unique to the New Zealand environment, are worthy of preservation irrespective of taxonomic status.

Captive breeding -- the last resort?

Human nature persists in leaving action on wildlife preservation until it becomes a matter of urgency. The propagation of endangered species in captivity is attempted too often at a late stage of population decline when recovery is uncertain. It takes enormous resources to avoid total loss of a species if there is not already a captive breeding population available. The California condor captive propagation project runs at a cost of $2 million per year and is now the only option left for this species. Similarly the Hawaiian crow (Alala) is all but extinct in the wild and attempts to breed them in captivity have not succeeeded to date. Instead of viewing captive breeding as a final alternative, we should realise that it takes years to develop techniques necessary to propagate a species. An understanding of behavioural constraints and nutritional requirements are vital to maintaining and breeding endangered species. When this option is left to a last resort, there is no longer the genetic background left in a wild population from which to draw founder members of a captive stock. Through the knowledge and experience gained over many years by aviculturalists at the National Wildlife Centre and keen members of Ducks Unlimited, the future of the blue duck and brown teal are at least assured in captivity. Methods of release back into the wild can be investigated. Unfortunately the same cannot be said for black stilts, kakapo and Campbell Island teal at present although captive breeding programmes are being intensified. A species taken from the wild and represented by captive individuals ceases to be a complete behavioural representation of that species. But at the very least, they still offer an accessible resource for public viewing and are a representation of a unique genetic form. We should heed the warning of Murray Williams and not leave action on any of our native species until too late for successful recovery. Instead of reallocating existing restricted resources from endangered to the less critical species, we should recognise the value of the former in generating further public support, financing, research and habitat acquisition to benefit all our native wildlife. p=

References

Pierce, R.J. 1982. A comparitive ecological study of Pied and Black Stilts in South Canterbury. PhD thesis, University of Otago. Pierce, R.J. 1986. Differences in susceptibility to predation during nesting between pied and black stilts (Himantopus spp.) The Auk 103: 273-280. Williams, G.R.; Given, D.R., 1981 The Red Data Book of New Zealand Nature Conservation Council, Wellington, New Zealand. 62 pp.