The reality of realty for parrots on Cayman Brac

Posted by Stuart Marsden

Recently, I have been working with Paul Watler of National Trust for the Cayman Islands and Dr Juliet Vickery of RSPB on a Darwin Initiative project looking at the status and conservation of the Near-threatened Cuban Parrot Amazona leucocephala and other birds on the tiny island of Cayman Brac in the Caribbean. 

Little Cayman from the tiny plane

The parrot on Cayman Brac is an endemic sub-species (A. l. hesterna) which was thought by
Cayman Islands Department of Environment to have a population of around 570 in 2012. It is threatened both by natural events such as hurricanes, and rather unnatural clearance of the island’s forest for housing developments.  The former can cause severe, but temporary, damage to the forest, particularly knocking down large old trees used by nesting parrots. The latter, of course, can destroy habitat for parrots and the island’s few other breeding landbirds, which, importantly, include the Near-threatened VitellineWarbler Setophaga vitellina, which is confined to the Caymans and the tiny Swan Islands, off Honduras.

 

Above: Parrot Estates offering plots in Cayman Brac. Below: Much of the island is for sale it seems.

The parrot surveys, nest searches and habitat measurements in the sweltering xeromorphic semi-deciduous forest of the Brac was just about the hardest fieldwork I have ever been involved with. It took us 20-30 minutes to cover just 100 metres. Nevertheless, Paul managed to accumulate a great dataset: nine active nests were found; forest birds were counted at 198 points; and potential nest site trees were recorded in forest across the island  in an attempt to identify the best areas for the Trust to try to purchase, to safeguard the parrot, in the future.

All these data will allow us to estimate population densities for key bird species in different habitats on the island, generate island-wide population size estimates, and, we hope, to gauge the likely effects on the island’s birds of potential real estate development over the next 20 years or so. While we hope to publish our full results in due course, our preliminary analyses point to several important findings 

A pair of Cuban Amazons stands guard 
at an active nest cavity

•  A high proportion of the island is owned by developers or potential developers

• Our initial population estimate for the parrot on the Brac is around 450 individuals, with the parrot occurring at a density of around 12 per sq km.

• Population densities of key landbirds were high – for example, perhaps in the order of 700 birds per sq km for Vitelline warbler, and 450 per sq km for Thick-billed Vireo Vireo crassirostris.

• The birds in general and the parrot in particular were not restricted to the least disturbed forests on the island.

Both high abundance and broad habitat use is something we would expect from birds on a small island with so few breeding land bird species. This is through processes known as ecological release and density compensation. It bodes reasonably well for the future of birds on the Brac – so long as real estate developments are not extensive, and those that do go ahead, retain native vegetation within the housing plots. Particularly important is retention of big old trees which contain cavities that may be used by the island’s parrots. Of course nobody can predict when the next big hurricane will strike the Brac, but the healthier the forest and its bird populations, the better they may be able to withstand its effects.

The project was coordinated by the National Trust for the Cayman Islands. For more information or to join, click here

The project was funded by Darwin Initiative 


Photos: Stuart Marsden

Timneh Parrot and Grey Parrot represent two species

Posted by Nigel Collar

When species are split into two or more new species, there can be serious implications for the conservation status of the newly elevated taxa. For a start, each of the new species will have a smaller range and a smaller population ‒ therefore increasing the chance that it will be considered ‘Threatened’ according to the IUCN Red List. In the case of grey parrots, it also has serious implications in terms of trade monitoring. Here, Nigel Collar of BirdLife International explains the scoring system he uses for taxonomic assignment and why the two ‘old’ subspecies of African Grey Parrot Psittacus erithacus erithacus and P. e. timneh are now recognised by BirdLife as two distinct species.

Using the scoring system of Tobias et al. (2010), BirdLife staff measured the degree of phenotypic differentiation between West African timneh and nominotypical erithacus using a system in which an exceptional difference (a radically different coloration, pattern or vocalisation) scores 4, a major character (pronounced difference in body part colour or pattern, measurement or vocalisation) 3, a medium character (clear difference reflected, e.g., by a distinct hue rather than different colour) 2, and a minor character (weak difference, e.g. a change in shade) 1; a threshold of 7 is set to allow species status, species status cannot be triggered by minor characters alone, and only three plumage characters, two vocal characters, two biometric characters (assessed for effect size using Cohen’s d where 0.2–2 is minor, 2–5 medium, 5–10 major and >10 exceptional) and one behavioural or ecological character may be counted (Tobias et al. 2010). Moreover, under this scheme a parapatric range (where two taxa replace each other across an extremely narrow line, with no gap between populations) scores 3, a narrow zone of hybridisation 2 and a broad zone of hybridisation 1 (these degrees of hybridisation without full character merging reflect different levels of genetic independence).

Left, Grey Parrot (photo: Keith Allison) and Right, Timneh Parrot (photo: Snowmanradio)

The form timneh can be considered distinct at the species level on account of its

•                     darker grey plumage (2);

•                     maroon (vs bright red) tail (3);

Left, Grey Parrot (photo:L. Miguel Bugallo Sanchez); Right, Timneh Parrot (Photo: Diana Sophia)

•                     smaller size (no score yet; measurements not taken);

•                     pinkish-grey (vs blackish) upper half of upper mandible (2);

Left, Grey Parrot (photo: Greg Glendell); Right, Timneh Parrot (Photo: Simon Brusland)

•                     parapatric distribution (now blurred owing to escapes of taxa either side of the line, but somewhere in eastern Côte d’Ivoire) (3).

The original description (by Fraser 1844) diagnosed the form by ‘its much darker tints of colouring, and the tail-feathers terminating in a point’, and this latter observation proves largely to be correct in specimen material in the Natural History Museum, Tring, with the shaft of each rectrix slightly protracted so as to give the feather tip the shape of a curly bracket (also known as braces, flower brackets and gullwings)—as in: }

Distribution range of Psittacus timneh and
Psittacus erithacus in West Africa (distribution data by BirdLife International)

This newly recognised taxon may already be in trouble. The only places across its range where we know for certain that there are ‘reasonable’ numbers of Timneh are the Gola Forest in Liberia/Sierra Leone and on the Bijagós Islands in Guinea-Bissau. Across much of the rest of its range, we either know that it is rare or totally absent, or we do not know about its status. It may well be pretty rare over much of Sierra Leone and Cote d’Ivoire, although it may be faring slightly better in Liberia. What we must do is to conduct research at key sites across its range to determine its status and conservation needs – this is now a high priority.

References

Fraser, L., 1844. Description of three new species of birds. Proc. Zool. Soc. London 12: 37-38

Tobias, J. A., Seddon, N., Spottiswoode, C. N., Pilgrim, J. P., Fishpool, L. D. C. & Collar, N. J. (2010) Quantitative criteria for species delimitation. Ibis152: 724-746.

Designing working landscapes with important birds in mind

Posted by Matt Geary

Species distribution modelling has become an invaluable tool in conservation science over the past decade. It has been widely used to delimit species' ranges, identify potential survey areas and predict future range-shifts due to climate change. Species distribution models have also been used to identify suitable habitat features for focal species and to suggest future management actions. In this paper, published in the latest issue of Ibis, we extended these ideas using multi-scaled models to 'design' landscapes for a species with complex habitat requirements, the black grouse.

Black grouse Tetrao tetrix is a medium-sized gamebird which has experienced serious population declines across western Europe over the last 100 years. In Britain populations are thought to have been negatively affected by land-use changes in the uplands, particularly canopy-closure in commercial plantation forests and increases in grazing pressure. Black grouse is a bird of the forest-edge and requires a habitat mosaic consisting of woodland, moorland, scrub and upland bog among other habitat types. Because of these complex requirements it can be difficult to assess habitat combinations for black grouse, never mind isolate one particular habitat mix.

Male black grouse in snow. Photo: Steve Garvie

Black grouse are relatively faithful to territories across years and compete for mates at traditional, communal display sites, within these territories, each spring. We used records of these territories (kindly provided by the volunteers at the Perthshire Black Grouse Study Group) along with habitat data from satellite imagery to fit species distribution models for black grouse within our study area in Perthshire, Scotland. We used MaxEnt to fit the models and performed the modelling at six radii around lek sites (between 0.2 and 3 km). We tried to identify habitat features which were associated with a high relative suitability for black grouse at each of these scales.

  

A view of the study area in Perthshire from Ben Vrackie. Photo: Jan Zeschky.

With this information we could start to show how habitat features in different parts of black grouse territories could contribute to the overall suitability of the landscape for black grouse. As you might expect, different habitat types were suitable at different proportions in different parts of our 'ideal' territory. Close to display sites, large proportions of several individual habitat types or varied habitat mixtures could all result in high relative suitability for black grouse. One habitat type in particular, though, was always detrimental at small distances from the lek. Closed canopy forestry in these locations reduced the suitability for black grouse, most probably because this sort of forestry would strongly reduce the visibility of the lek site. Dense commercial forests are very difficult for black grouse to move through and where these forests have hard edges they prove difficult to use as a refuge from predators. These factors would all be detrimental close to a display site.

   

Caledonian pine forest in North Scotland. Open canopy forestry with a rich understorey

At larger distances from the lek, however, larger proportions of forestry become acceptable. We also found that, while closed-canopy forestry might not be suitable close to the lek, at moderate distance a relatively large amount of open-canopy forestry, such as native woodland, would be less damaging. We also identified more than one habitat combination which could result in large or growing black grouse leks. Through use of multi-scaled models, we were able to consider a range of habitat mosaics which have the potential to be beneficial for this species. We believe that the messages from this study translate well across bird species. Combining landscape-scale conservation, translated into policy for example, with fine-scale habitat management can benefit not only individual groups but contiguous populations of species and ensure their survival into the future.

Photo: Billy Lindblom

Matt Geary finished his PhD at MMU last year. He used a range of modelling methods to assess the long-term viability of black grouse populations in the face of changes to the Scottish uplands. The PhD was funded by Manchester Metropolitan University and the World PheasantAssociation. Matt is now a lecturer in Conservation Biology and Animal Behaviour at the University of Chester. Contact him at M.Geary@Chester.ac.uk. More information about his research is at http://mattgeary.github.com.