Current view: Data table and detailed info
Taxonomic note
Has been separated in Natalornis, on basis of sexual dimorphism, distinctive plumage (without rufous, no white in tail), nest structure and egg coloration; within present genus, however, these features (apart from nest structure) are variable, suggesting that separate genus is not warranted. DNA data (Dor et al. 2010) indicate sister relationship with H. nigrorufa, despite striking morphological differences. N population, with plumage washed violet, sometimes separated as subspecies lynesi, but differences insignificant. Monotypic.
Taxonomic source(s)
del Hoyo, J., Collar, N.J., Christie, D.A., Elliott, A., Fishpool, L.D.C., Boesman, P. and Kirwan, G.M. 2016. HBW and BirdLife International Illustrated Checklist of the Birds of the World. Volume 2: Passerines. Lynx Edicions and BirdLife International, Barcelona, Spain and Cambridge, UK.
IUCN Red List criteria met and history
Red List criteria met
Red List history
| Migratory status |
full migrant |
Forest dependency |
does not normally occur in forest |
| Land-mass type |
continent
|
Average mass |
14 g |
Population justification: Numbers for each country are assessed and revised below, resulting in an updated estimate based on information from the breeding range of 1,564-3,074 mature individuals, rounded here to 1,500-3,000 mature individuals. The large range reflects the considerable uncertainties within the available data, especially in Zimbabwe and Malawi. Uncertainty over the population in DR Congo is not addressed here due to the lack of data, rather the value based on expert opinion (Evans et al. 2015) is retained unqualified. The total population has previously been estimated at between 1,169 and 1,338 pairs (Evans et al. 2016), equivalent to a population size of 2,338-2,676 mature individuals.
In deriving the revised population estimate here data used was in the form of individuals observed during the breeding season, where it is reasonable to equate numbers observed with mature individuals for this species (Evans 2008, Evans et al. 2016). The number of breeding pairs might be overestimated if the number of adult birds counted during a survey are converted to breeding pairs without taking the potential for cooperative breeding, frequently noted in parts of the range but not others (Evans et al. 2016), into account. However, as helpers are assumed to be capable of breeding should the opportunity arise and the population size is treated as the number of mature individuals, no adjustment to account for cooperative breeding is applied here. While the previous population size was conservatively placed in the band 1,000-2,499 mature individuals given the uncertainty over estimated numbers (BirdLife International 2016), the appraisal of available data from the whole breeding range indicates the minimum value was too low.
The species has been treated as occurring in multiple subpopulations on the basis of high natal fidelity (Evans et al. 2015). Three subpopulations were tentatively identified by Evans and Bouwman (2010): 1, those breeding in southeastern Democratic Republic of Congo and suspected to winter on the Lendu Plateau (c. 200 mature individuals); 2, those breeding in southeastern Malawi and southern Tanzania (Livingstone Mountains and Udzungwa Mountains) and wintering in Kenya and SE Uganda; and 3, those breeding in South Africa, Eswatini, Mozambique, northern and southwestern Malawi and southwestern Tanzania and wintering in southwestern Uganda. The latter grouping was separated on the basis of geographic distance by Evans et al. (2015) giving four 'clusters', however individuals from both the South Africa/Eswatini and Malawi/Tanzania breeding populations were suggested to have been found within a very small sample identified in from the same non-breeding area through stable isotope analysis (Wakelin et al. 2011), although that adult birds had been demonstrated to moult solely in non-breeding areas (Earle 1987) appears to undermine this finding (S.W. Evans in litt. 2023). However, there seems little biogeographic explanation for a division between those breeding in different parts of Malawi and Tanzania. While hypothesised to spend the non-breeding season on either side of Lake Victoria (Evans and Bouwman 2010), it may be that individuals wintering here originate from multiple breeding areas, as there is no apparent biogeographical barrier to birds coming from the south and therefore no barrier to mixing of dispersing birds. The apparent shift of non-breeding individuals into the Masai Mara National Park (Evans et al. 2015, eBird 2023) supports the suggestion that there may be movement between sites in the nonbreeding season. Logically this suggests that most of the population is subject to some level of exchange of individuals and therefore operate as a single subpopulation (per IUCN 2022). The separation noted for birds within the Democratic Republic of Congo (breeding in the southeast and occurring on the Lendu Plateau in the non-breeding season) suggests this may be a separate subpopulation. Comprising only around 200 mature individuals (though poorly evaluated), this would represent a maximum of 13% of the global population. However, in the knowledge that the species is fully migratory, capable of significant dispersal and that there is no firm evidence of subpopulation structure within the species, the precautionary position is adopted here and the species is assessed as a single subpopulation.
The largest reported breeding numbers are in Malawi, southern Tanzania and eastern Zimbabwe. In Malawi, most breed within Nyika National Park, where 28 territories were located in 71 km2 in 1987 (Holroyd and Quinn, n.d.), with this used to generate a population of between 204-260 pairs for the central plateau above 2,200 m indicating that approaching 300 pairs were probably present (Fishpool and Evans 2001). The same data were used to suggest that given the amount of suitable habitat above 2,100 m at least 300 pairs are likely present (Dowsett-Lemaire 2006). A survey of Nyika National Park in January and February 2004, qualified as short (16 days) and noted to not cover the dry season, recorded 59 individuals but no attempt was made to derive an overall population size (Anon. 2005). It is possible that the specificity of suitable nest-sites for the species may mean that extrapolation from an apparent high density of nests in one area is inappropriate. A precautionary revision would be to halve the minimum value, suggesting a rounded preliminary figure between 100 and 300 pairs present, or 200-600 individuals. Additionally small numbers breed in Misuku Hills, North and South Viphya, Kirk Range and Mount Mulanje, with a value of 40 pairs/80 individuals assigned to sites in Malawi away from Nyika (Evans et al. 2015).
In southern Tanzania, surveys in 2008/9 and 2012 generated a total of 151 individuals observed in an estimated 1,905 km2 covered, with a habitat suitability model predicting a total suitable area of between 7,598-17,177 km2 and therefore a population between 602 and 1,362 individuals (Evans et al. 2016). There is one potential bias unaccounted in this data: that the transect route was not representative of the modelled suitable habitat area (Evans et al. 2016), however given the wide variance in potentially suitable habitat area used a significant error is unlikely.
Numbers in the eastern highlands of Zimbabwe were given as 620 individuals in Evans et al. (2015). Much of this is comprised of an estimated 200 pairs in Nyanga National Park and an additional 100-200 pairs patchily along the remainder of the highlands (Childes 2001, Mwizabi et al. 2003). However, Childes (2001) reported a total of 400 birds in 1988 having reduced to 271 by 1996, with 71 pairs reported from the Nyanga IBA in 2001 (per Mudereri et al. 2009). A survey was conducted in 2013/14 across the known sites within the country, recording 175 individuals from Nyanga in a surveyed area of 75 km2, suggesting that the total number of pairs at this time likely exceeded 71 but does suggest a decline since 1988 (Matsvimbo et al. 2014). Significant loss of grassland across the area is noted as the driver of the decline (Matsvimbo et al. 2014). The 2013/14 survey recorded 34 individuals in a surveyed area of 5 km2 in Chimanimani and only 4 individuals in each of Stapleford forest area and the Bvumba Highlands (Matsvimbo et al. 2014). At the latter site the species now appears to be restricted to a single site, with Matsvimbo et al. (2014) stating the future looks bleak for the species in the Bvumba highlands, and the survey also found little potential for larger numbers in the Stapleford forest area. This survey suggests that at a considerably lower minimum number of individuals is required to capture the potential reduction in the Zimbabwe population for this reassessment. A range of 100-200 pairs/200-400 mature individuals is assigned to Nyanga, 50-150 individuals at Chimanimani and with 10-50 mature individuals at the remaining sites, giving a precautionary revised country total of 260-600 individuals.
There is limited habitat in Zambia hence few individuals, 20-30 (Mwizabi et al. 2003), and these are considered contiguous with the Nyika plateau population (Evans et al. 2015). While there is a lack of proper survey data, very few have been observed recently suggesting even fewer, 10-15 may be present (F. Willems in litt. 2024).
In Mozambique the estimate of 50 pairs/100 individuals is considered a minimum estimate and previous reported numbers have been similar (Evans and Bouwman 2010, Little 2013, Allport et al. 2021). These are found in four or five sites, with 10-15 pairs in Catandica and Serra Choa, 25-30 pairs at 'Penhalonga' in Manica, 1-3 pairs at Mt. Tsetserra, likely breeding in the Mozambique side of Chimanimani and possible breeding in the vicinity of Mt. Gorongosa (Allport et al. 2021).
Recent, rapid declines have been recorded in the southern portion of the breeding range, estimated at 54% over 7 years between 2005 and 2012, which would equate to 77 % over 10 years (Evans et al. 2015). The population in South Africa and Eswatini was estimated at around 100 pairs (Monadjem et al. 2006) around 2000, with 84 pairs recorded in South Africa (Anon. 2005b, M. McNamara in litt. 2006) and 106 pairs in 2005 (Evans et al. 2015). By 2012 this figure was 57 pairs (Evans et al. 2015), though elsewhere was thought to potentially be only 40 pairs (McKechnie and Little 2012). Evans (2015) placed the number at between 35-50 pairs, and Evans et al. (2015) reported 39 pairs in South Africa and 12 in Eswatini, hence 102 individuals down from 84 and 22 pairs respectively in 2005. The most recent information suggests there are between 35-40 pairs in South Africa (Anon. 2021), consistent with Evans et al. (2015).
Declines are thought to be occurring in Zimbabwe (Matsvimbo et al. 2014) and also possibly Mozambique (Evans et al. 2015) but this is uncertain given the need for further survey (Allport et al. 2021). In Malawi/Zambia the important population around Nyika is thought stable and there is no evidence for a contraction in breeding range for southwestern Tanzania (Evans et al. 2015). No information on any change in the population breeding in DR Congo is available.
Numbers in non-breeding areas are poorly monitored. The species has ceased wintering around Mabira Forest and apparently also from the Busia Grasslands, attributed to loss of grassland habitat to grazing and agriculture (Ogoma 2013a), although the species was reported to still occur by the local community. However the species now occurs in the Masai Mara in Kenya and Serengeti National Park in Tanzania, apparently a recent change to the non-breeding distribution given the high level of visitation to these protected areas (Evans et al. 2015).
Based on an analysis of the change in occupied sites over the full historical span of records, an annual rate of population reduction was derived of between 0.36% overall (1850-2005) and 0.64% for South African and Eswatini if the start of declines is set to 1890 to coincide with the onset of commercial forestry expansion (Evans and Bouwman 2010). Loss of the suitable habitat to agriculture and forestry is continuing today (Monadjem et al. 2006, Evans 2015, Evans et al. 2015). Based on a linear model of reduction the population is suspected to be declining at between 4-6 % over ten years (Evans and Bouwman 2010), while a population viability model predicted an ongoing rate of 8 % decline (Evans et al. 2015). In conjunction with the rapid rate of reduction noted in the south of the breeding area these analyses infer that there is an overall continuing decline in the population.
Trend justification: Based on an analysis of the change in occupied sites over the full historical span of records, an annual rate of population reduction was derived of between 0.36% overall (1850-2005) and 0.64% for South African and Eswatini if the start of declines is set to 1890 to coincide with the onset of commercial forestry expansion (Evans and Bouwman 2010). Loss of the suitable habitat to agriculture and forestry is continuing at this slow to moderate rate today (Monadjem et al. 2006). Based on a linear model of reduction the population is suspected to be declining at between 4-6 % over ten years (Evans and Bouwman 2010), while a population viability analysis approach yielded an 8% decline in 10 years, and an overall probability of extinction over the 100 years from 2005-2105 of 3% (Evans et al. 2015). An overall continuing decline is inferred from these analyses.
While this rate of decline appears relatively slow, recent very rapid declines (52% in 10 years in South Africa and Eswatini) have been recorded in the southern part of the breeding range (Evans and Bouwman 2010, Evans 2015, Evans et al. 2015, Anon. 2021). In 2000 the population in South Africa and Eswatini was estimated at 240 mature individuals (Evans and Barnes 2000) and in 2005 at 106 pairs (Evans et al. 2015). By 2012 this figure was 57 pairs (Evans et al. 2015), and only 35-40 pairs were present in South Africa in 2021 (Anon. 2021), with very few now in Eswatini (down to presence in a single quarter degree grid cell) (Evans et al. 2015) and multiple years with no nests located even before this (J. Wakelin in litt. 2007).
There is no evidence of a decline in range and by inference population in the core breeding areas in Tanzania, Malawi and Zambia (Evans et al. 2015, 2016: though F. Willems in litt. [2024] reports a decrease is more likely than stability in the latter country), but there is little information on the population in DR Congo (Evans et al. 2015). However, the limited survey effort that has taken place within Zimbabwe does suggest that a significant decline has taken place: Childes (2001) reports totals of 400 individuals in 1988 but only 271 recorded in 1996, while a more recent survey recorded 175 individuals in 2013/14 (Matsvimbo et al. 2014).
Given the very rapid declines observed in best monitored parts of the range and much lower monitoring effort in the core of the range it is suspected that the overall recent and ongoing rate of decline may be greater than that predicted by the historical range change information and the population viability analysis. To reflect this and the uncertainty, the rate of population reduction over the past, current (using 2016 as the start year) and future three generations is placed in a band of 5-20%. Regular monitoring is required in the areas with the largest numbers of breeding pairs.
Country/territory distribution
Important Bird and Biodiversity Areas (IBA)
Recommended citation
BirdLife International (2024) Species factsheet: Blue Swallow Hirundo atrocaerulea. Downloaded from
https://datazone.birdlife.org/species/factsheet/blue-swallow-hirundo-atrocaerulea on 22/12/2024.
Recommended citation for factsheets for more than one species: BirdLife International (2024) IUCN Red List for birds. Downloaded from
https://datazone.birdlife.org/species/search on 22/12/2024.
