From 2018 to 2022, Vicente dos Santos Teixeira determined the actual geographical distribution and population numbers of golden-headed lion tamarins as part of his doctoral thesis. In addition, a vegetation characterization of realized and potential habitats was carried out. The aim of the work was to estimate the actual geographical range and population numbers, to determine the factors limiting the distribution of golden-headed lion tamarins and to identify current threats. The doctoral thesis ("Distribution limits, population estimation and influence of landscape attributes on the occurrence of the endangered golden-headed lion tamarin") has now been published. This work is of particular importance to AMAP, as the results will enable AMAP to identify the areas whose conservation is crucial for the long-term survival of the golden-headed lion tamarin. Based on this, we can design and implement conservation projects, e.g. reforestation of wildlife corridors or buffer zones. As the results of the doctoral thesis show, this is also urgently needed.
The results show that the population numbers and the distribution area have declined considerably. Compared to the last survey in 1993, the population size has decreased from 40-54,000 individuals to 16,522-21,822 individuals, and the distribution area has decreased from 22,700 km² to 13,215 km². This corresponds to a 42% decline in distribution and a 60% decline in population over the last 30 years. The available habitat for golden-headed lion tamarins has been estimated at 395,450 ha, with 96% (378,600 ha) of this area in the eastern part of its range and 4% (16,850 ha) in the western part. The eastern, coastal part of the habitat is characterized by cabrucas as a landscape matrix. The western part of the distribution area is dominated by cattle farming, remaining relict forests are highly fragmented, which means that the remaining populations of golden-headed lion tamarins are highly isolated and threatened with extinction. Only 8 % (30,451 ha) of the habitat is under protection. These are the Una Nature Reserve, the Sierra das Lontras National Park and the Boa Esperança Municipal Park.
In addition to the conversion of cabrucas into other forms of use such as eucalyptus plantations and cattle farming, the intensification of cocoa cultivation and the associated simplification of the vegetation structure of the existing cabrucas is considered to be the cause of the decline in the population. Especially since the amendment of the forest law in 2014, which made it possible to reduce the number of shade trees in the cabruca to at least 40 trees per hectare in order to increase productivity. Traditional cabrucas in southern Bahia have an average of 197 shade trees per hectare (with a variance of 70-480 trees), but a much higher density of shade trees and thus also biodiversity. Due to the establishment of a minimum density and thus the possibility of logging, cabruca are becoming increasingly structurally simplified and are less suitable as habitats for native fauna or as corridors. A reduction in the number of large shade trees in cabrucas also has a negative impact on habitat suitability for golden-headed lion tamarins, as Almeida et al. showed in 2020.
During the survey, it was shown, as already by Raboy et al. 2010, that golden-headed lion tamarins can also use habitats at higher altitudes (above 500m). In light of ongoing habitat destruction due to anthropogenic activities, forest fragments and cabrucas at higher altitudes can serve as refuges and be considered as potential conservation areas. The original distribution area covers altitudes up to 1100 m, which are rather unsuitable for agriculture and pasture farming. However, potential habitats must first be recorded here.
The occurrence of a population of golden-headed lion tamarins in the "Mata de Cipó", the transition from the Mata Atlântica biome to the Caatinga biome, far west of the actual distribution area and all other habitats, is astonishing. This area is drier than all other habitats, typical food resources (fruit-bearing trees and bromeliads) as present in cabrucas and other forest fragments are severely limited here and could restrict long-term survival, it is unclear how large the population is and how long it has existed in this fragment. Previous surveys have not detected any golden-headed lion tamarins here. If this population has always existed and has not been introduced, further ecological and behavioral studies are needed to clarify which abilities and factors are crucial for their survival in this habitat.