Santa Marta Screech-owl (Megascops gilesi) was first collected in 1919 in the Sierra Nevada de Santa Marta in northern Colombia, but was preliminary classified as Tropical Screech-owl (Megascops choliba). Based on the vocalisation and on genetic and morphological analysis of a second specimen taken in 2007 (Dantas et al. 2016, Krabbe 2017), the taxon was described as a new species in 2017 (Krabbe 2017).
Santa Marta Screech-owl inhabits humid forest at altitudes of 1,800-2,500 m (Krabbe 2017). To date, the species has only been observed on the San Lorenzo ridge in the north-western part of the Sierra Nevada de Santa Marta; however, it is likely that the species occurs in suitable habitat throughout the entire Santa Marta mountains, maybe even ranging to higher elevations than 2,500 m (Krabbe 2017).
Forests in the Sierra Nevada de Santa Marta have been heavily logged in the past, with only around 15% of the original vegetation remaining. Human encroachment in the area, which was accompanied by logging and burning of forests, began in the 1950s (Dinerstein et al. 1995, P. G. W. Salaman in litt. 1999, Snyder et al. 2000). Forests have been converted for the expansion of non-native tree plantations, such as pine and eucalyptus, and cleared for livestock farming (C. Olaciregui in litt. 2012). However, an analysis of the rate of forest loss between 2000 and 2012 found that deforestation in the Sierra Nevada de Santa Marta was only minor (per Tracewski et al. 2016), indicating that the area of remaining forests is stable, albeit small and fragmented.
Here, we present our assessment against all criteria for the newly described Santa Marta Screech-owl.
Criterion A – The population trend of Santa Marta Screech-owl has not been quantified, and therefore the species cannot be correctly assessed against Criterion A. While the remaining forested habitat within its range is likely only declining slowly (per Tracewski et al. 2016), the species is assumed to be threatened by the high degree of forest fragmentation and degradation in the Sierra Nevada de Santa Marta. Therefore, we can precautionarily suspect that the species is undergoing a slow decline.
Criterion B – The Extent of Occurrence (EOO) of this species has been calculated at 5,020 km2. This meets the threshold for Vulnerable under Criterion B1 (EOO < 20,000 km2). The Area of Occupancy (AOO) has not been estimated, and therefore the species cannot be assessed against Criterion B2. However, in order to be listed as Vulnerable under Criterion B1, other conditions have to be met.
The subpopulation structure has not been assessed, so it is unclear whether the species meets condition (a). Records on eBird (2019) suggest however that the species forms at least two relatively large subpopulations and thus cannot be considered severely fragmented sensu IUCN (most individuals are found in small and isolated subpopulations; IUCN 2012). The most serious plausible threat to the species is the loss and fragmentation of its forest habitat. Deforestation and illegal logging are site-specific and take place on a relatively small geographic scale; consequently we can conclude that the species is threatened in different areas by different logging events, and thus occurs in several locations*. However, given the small extent of the known range, it is highly likely that the species does not occur in >10 locations*. Therefore, the species meets the condition (a). Even though the rate of forest loss is likely low (per Tracewski et al. 2016), the species is assumed to be undergoing a decline in habitat quality and population size, meeting condition b(iii,v). There is no evidence that the species is undergoing extreme fluctuations, so it does not fulfil condition (c). Consequently, Santa Marta Screech-owl may be listed as Vulnerable under Criterion B1ab(iii,v).
Criterion C – The population size of this species has not been directly quantified. We can, however, derive a preliminary estimate based on the area of mapped range, habitat availability and population density of congeners. The mapped range (not equivalent to EOO) of Santa Marta Screech-owl covers an area of c.4,500 km2. Given that only about 15% of the original forests are remaining in the area, we can conclude that there is c.675 km2 of suitable habitat remaining within the range. Density estimates are available for the closely related Tawny-bellied Screech-owl (Megascops watsonii), ranging from 1.75 pairs/km2 in French Guiana to 5.5 pairs/km2 in Peru (Santini et al. 2018). We can preliminarily assume that Santa Marta Screech-owl occurs at a similar density, i.e. at 1.75-5.5 pairs/km2, which equates to 3.5-11 mature individuals/km2. Given the availability of suitable habitat for Santa Marta Screech-owl, the population may number c.2,300-7,500 mature individuals. Assuming that the true population size is closer to the lower end of the estimate, this meets the threshold for listing as threatened under Criterion C. However, in order to be listed under this criterion, other conditions have to be met.
The population is suspected to be in slow decline. The level of confidence is therefore too low to qualify for listing as threatened under Criterion C. However, in case that other conditions are met, the species might still be considered Near Threatened. As we do not have any data on the rate of decline, Santa Marta Screech-owl cannot be compared against Criterion C1. It therefore depends on the subpopulation structure if the species qualifies for Criterion C2. Data from eBird (2019) show two large subpopulations in the western part of the Sierra Nevada de Santa Marta, but it has been suggested that the species may occur throughout the massif (Krabbe 2017). While condition 2a(ii) is not met, we can preliminarily and very precautionarily assume that no subpopulation contains more than 1,000 mature individuals, or at least approaches this threshold. Thus, the species would meet or approach condition 2a(i). There is no evidence that the species is undergoing extreme fluctuations; thus condition 2b is not met.
Overall, unless new information on the population size and structure becomes available, the species may be considered Near Threatened, approaching the threshold for listing as threatened under Criterion C2a(i).
Criterion D – The population size and range of Santa Marta Screech-owl are too large to qualify for listing as threatened under Criterion D. Therefore, the species may be considered Least Concern under this criterion.
Criterion E – To the best of our knowledge no quantitative analysis of extinction risk has been conducted for this species. Therefore, it cannot be assessed against this criterion.
Therefore, it is proposed that Santa Marta Screech-owl (Megascops gilesi)be listed as Vulnerable under Criterion B1ab(iii,v). We welcome any comments on this proposed listing and specifically request information on the population size and trend of the species.
Please note that this topic is not designed to be a general discussion about the ecology of the species, rather a discussion of its Red List status. Therefore, please make sure your comments are relevant to the discussion outlined in the topic.
*Note that the term ‘location’ defines a geographically or ecologically distinct area in which a single threatening event can rapidly affect all individuals of the taxon present. The size of the location depends on the area covered by the threatening event and may include part of one or many subpopulations. Where a taxon is affected by more than one threatening event, location should be defined by considering the most serious plausible threat (IUCN 2001, 2012).
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