Browsing by Autor "Tjalle Boorsma"

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Breeding and global population sizes of the Critically Endangered Red-fronted MacawAra rubrogenysrevisited
(Cambridge University Press, 2022) Sebastián K. Herzog; Tjalle Boorsma; Guido Saldaña-Covarrubias; Tomás Calahuma-Arispe; Teodoro Camacho-Reyes; Dirk Dekker; Suzanne Edwards de Vargas; Máximo García-Cárdenas; Víctor Hugo García-Solíz; Jazmín M. Quiroz-Calizaya
Summary The ‘Critically Endangered’ Red-fronted Macaw is endemic to seasonally dry, rain-shadowed valleys in the south-central Andes of Bolivia. The remoteness and inaccessibility of most of this region have hampered the rigorous collection of reliable range-wide data on the species’ global, local and breeding population sizes. Such data are imperative, however, for effective conservation and management. Estimated to number up to 5,000 birds in the early 1980s, the most recent and thorough survey to date reported a total of only 807 macaws and a breeding population fraction of about 20% in 2011, disjunctly distributed across eight breeding and six foraging areas and divided into four genetic clusters. Ten years later, we reassessed the species’ population sizes and breeding distribution with increased survey effort and geographic coverage. Six teams simultaneously surveyed different sections of the species’ entire known breeding range in four watersheds focusing on nesting sites. We estimated a global population size of 1,160 macaws, a breeding population fraction of 23.8–27.4% (138–159 nesting pairs) and discovered four new breeding areas. Watersheds and breeding areas differed widely in nesting pair and total macaw numbers. The Mizque watershed held 53% of the species’ breeding and 41.5% of its global population and had the highest breeding population fraction of 30.7–34.9%; the Pilcomayo watershed obtained the lowest values (6%, 8.5% and 14.1–18.2%, respectively). Two of the four documented genetic clusters (subpopulations) each held well over 50 breeding individuals. Two of the eight breeding areas documented in 2011 were found unoccupied in 2021. Numbers of nesting pairs per breeding area in 2011 were poorly correlated with those in 2021, and timing of breeding activities also differed between years. Our new data indicate that the Red-fronted Macaw no longer meets IUCN Red List criteria for ‘Critically Endangered’ species and that it should be downlisted to ‘Endangered.’
Cattle affect regeneration of the palm species Attalea princeps in a Bolivian forest–savanna mosaic
(Wiley, 2019) Iris Hordijk; Fabian Meijer; Esther Nissen; Tjalle Boorsma; Lourens Poorter
Abstract Attalea princeps is an important palm species that shapes the forest–savanna mosaic in Beni, Bolivia, as it dominates the two principal forest landscape elements (forest islands and gallery forest), and provides a vital microhabitat, food, and nesting source for numerous plant and animal species. The forest–savanna mosaic is used for extensive grazing, and the palm population is declining on the forest islands due to a low regeneration rate, which threatens the maintenance of this landscape. We therefore examined the (a)biotic factors that influence the population structure of Attalea in the centers and edges of forest islands and gallery forests. Ninety‐one 0.1‐ha plots were established, and 500 palm adults and 3,700 juveniles were measured for their size, health condition, and fire damage. For each plot, habitat characteristics, such as landscape position, grazing pressure, and soil conditions, were measured. Attalea population density was significantly lower on the forest islands than in the gallery forests, especially in the juvenile life stage. A structural equation model showed that juvenile density is positively related to the health condition of juveniles and amount of fruits present, where the amount of fruits is positively affected by the condition of adults. Juvenile density is negatively influenced by grazing, affecting the health condition of the juvenile, as well as organic matter and phosphate availability in the soil. Therefore, it is recommended to decrease the grazing pressure by decreasing livestock densities, fencing off vulnerable forest islands, or by rotating cattle.Abstract in Spanish is available with online material.
Deterministic population growth models and conservation translocation as a management strategy for the critically endangered Blue-throated Macaw (Ara glaucogularis): A critique of Maestri et al.
(Elsevier BV, 2018) Sebastián K. Herzog; Jens Bürger; Alejandra J. Troncoso; Renzo R. Vargas; Tjalle Boorsma; Rodrigo Wilber Soria-Auza
First report of a leucistic Brown Agouti (Dasyprocta variegata) in Bolivia
(De Gruyter, 2024) Jente Ottenburghs; Edward Smits; Mark van Leeuwen; Tjalle Boorsma; Luz Natalia Mercado Callaú; Miguel Martinez Diaz; Peter van der Sleen
Abstract Cases of anomalous coloration are regularly reported in Neotropical mammals, including the rodent family Dasyproctidae (agoutis and acouchis) where leucistic and albino individuals have been observed. Here, we document the first case of leucism in the Brown Agouti ( Dasyprocta variegata ) in Bolivia. During a camera trap survey of the Barba Azul Nature Reserve, we obtained footage of a Brown Agouti with a completely white body. Additional pictures of this individual revealed that it has black eyes, indicating leucism instead of albinism. Previous observations (since 2017) of a white agouti in the area suggest that these anomalously colored individuals can survive in the wild. Rare observations of top predators suggest a relatively low predation pressure in the area. We had only one record of a South-American Puma ( Puma concolor ) during our camera trap survey. Hence, leucistic individuals of a common prey species might also be indicative of the dwindling population densities of top predators in the region.
First systematic sampling approach to estimating the global population size of the Critically Endangered Blue-throated MacawAra glaucogularis
(Cambridge University Press, 2020) Sebastián K. Herzog; Oswaldo Maillard Z.; Tjalle Boorsma; GUSTAVO SÁNCHEZ-ÁVILA; Víctor Hugo García-Solíz; Anahi Cosky Paca‐Condori; MARTA VAÍLEZ DE ABAJO; Rodrigo Wilber Soria-Auza
Summary Reliable population size estimates are imperative for effective conservation and management of globally threatened birds like the ‘Critically Endangered’ Blue-throated Macaw Ara glaucogularis. Endemic to one of South America’s largest grassland floodplains, the Llanos de Moxos in northern Bolivia, the species’ global population size is uncertain. The region’s inaccessibility renders the application of traditional methods for obtaining bird population estimates impracticable or cost prohibitive. We developed a simultaneous, multilocality, double-sampling approach combined with quantitative habitat availability analyses to obtain the first rigorous population size estimate for the Blue-throated Macaw. We established 11 survey areas across its three subpopulations that were visited twice by one team in each subpopulation over a 23-day period in the 2015 dry season and obtained additional count data from two roost sites. We classified suitable habitat (palm forest islands) using Landsat 8 images and CLASlite forest monitoring software. We extrapolated the number of macaws detected (conservative estimate of the total number of macaws [CETN], highest single count [HSC]) per 100 ha of suitable habitat in each survey area to the entire area of suitable habitat in all subpopulations combined, corrected for the species’ range occupancy of 34.3%. The total number of Blue-throated Macaws detected by survey (CETN) and roost site counts was 137. Across all survey areas, the number of macaws per 100 ha of suitable habitat was 4.7 for the first and 4.4 for the second period for CETN and 3.2 and 3.4, respectively, for HSC data. Corresponding global population estimates were 426–455 (CETN) and 312–329 (HSC) individuals. Other recent research and anecdotal data support these estimates. Although it would be premature to propose downlisting the species to ‘Endangered’, our findings indicate that it has a larger population and slightly larger range than previously thought, and that the positive effects of conservation actions are now becoming apparent.
Priorities for translating goodwill between movement ecologists and conservation practitioners into effective collaboration
(Society for Conservation Biology, 2022) Rascha J. M. Nuijten; Todd E. Katzner; Andrew M. Allen; Allert I. Bijleveld; Tjalle Boorsma; Luca Börger; Francesca Cagnacci; Tom Hart; Michelle Henley; Richard M. Herren
Abstract Addressing ongoing biodiversity loss requires collaboration between conservation scientists and practitioners. However, such collaboration has proved challenging. Despite the potential importance of tracking animal movements for conservation, reviews of the tracking literature have identified a gap between the academic discipline of movement ecology and its application to biodiversity conservation. Through structured conversations with movement ecologists and conservation practitioners, we aimed to understand whether the identified gap is also perceived in practice, and if so, what factors hamper collaboration and how these factors can be remediated. We found that both groups are motivated and willing to collaborate. However, because their motivations differ, there is potential for misunderstandings and miscommunications. In addition, external factors such as funder requirements, academic metrics, and journal scopes may limit the applicability of scientific results in a conservation setting. Potential solutions we identified included improved communication and better presentation of results, acknowledging each other's motivations and desired outputs, and adjustment of funder priorities. Addressing gaps between science and implementation can enhance collaboration and support conservation action to address the global biodiversity crisis more effectively.
Satellite Telemetry of Blue-Throated Macaws in Barba Azul Nature Reserve (Beni, Bolivia) Reveals Likely Breeding Areas
(Multidisciplinary Digital Publishing Institute, 2021) L. Davenport; Tjalle Boorsma; Lucas A. Carrara; Paulo de Tarso Zuquim Antas; Luciene Carrara Paula Faria; Donald J. Brightsmith; Sebastián K. Herzog; Rodrigo Wilber Soria-Auza; A. Bennett Hennessey
The Blue-throated Macaw (Ara glaucogularis) is a Critically Endangered species endemic to the Llanos de Moxos ecosystem of Beni, Bolivia. To aid conservation of the northwestern population that utilizes the Barba Azul Nature Reserve during the non-breeding season, we set out to learn the sites where these birds breed using satellite telemetry. We describe preliminary tests conducted on captive birds (at Loro Parque Foundation, Tenerife, Spain) that resulted in choosing Geotrak Parrot Collars, a metal, battery-operated unit that provides data through the Argos satellite system. In September 2019, we tagged three birds in Barba Azul with Geotrak collars, and received migration data for two birds, until battery depletion in November and December 2019. Our two migrant birds were tracked leaving Barba Azul on the same date (27 September), but departed in divergent directions (approximately 90 degrees in separation). They settled in two sites approximately 50–100 km from Barba Azul. Some details of the work are restricted out of conservation concern as the species still faces poaching pressures. Knowing their likely breeding grounds, reserve managers conducted site visits to where the birds were tracked, resulting in the discovery of breeding birds, although no birds still carrying a transmitter were seen then. A single individual still carrying its collar was spotted 13 August 2021 at Barba Azul. The work suggests that the Blue-throated Macaws of Barba Azul use breeding sites that are scattered across the Llanos de Moxos region, although within the recognized boundaries of the northwestern subpopulation. We conclude that the use of satellite collars is a feasible option for research with the species and could provide further conservation insights.