SPECIES

Swynnerton's Robin Swynnertonia swynnertoni Scientific name definitions

Flemming P. Jensen
Version: 2.0 — Published February 4, 2022

Demography and Populations

Introduction

Generally a low-density species with the majority occurring in a rather narrow zone between approximately 1,200–1,700 m elevation. The total population likely includes around 6,000 birds (see Population Status), the majority of which occurs in Tanzania’s Udzungwa Mountains. Only in a few forests in Zimbabwe and Tanzania is it known to be locally common. However, because it is generally an unobtrusive and quiet bird with a subdued song, it is likely sometimes overlooked so populations may be underestimated.

Measures of Breeding Activity

In Zimbabwe, young birds appear not to breed until they are about 2 years old (1, 3). In a ringing study in Zimbabwe, 4 pairs were repeatedly recaptured in their respective territories over 3–8 yr (3). Clutch typically 2 eggs, occasionally 3 eggs. Normally one brood per year, but the species is certainly double brooded at times (1).

Life Span and Survivorship

Among ringed birds in eastern Zimbabwe, the oldest (a female) was recaptured at approximately 10 years old; a more than 9 year-old male was recaptured during the same study (3).

Disease and Body Parasites

No information.

Causes of Mortality

No information.

Population Spatial Metrics

No information.

Population Status

The total population is estimated at around 6,000 birds, the majority of which occurs in the Udzungwa Mountains of Tanzania.

S. s. swynnertoni

In Mozambique, the population on Mt. Gorongosa was previously considered large (21), but the number of birds is expected to be lower due to destruction of much of the highland forest. In 1970, upper moist forest on Mt. Gorongosa was estimated to cover 125 km2 (T. Oatley, in litt. 1999 in17), but in 2007 only ~80 km2 of remained from 900 to 1,800 m (22). In 2005, Parker estimated that the Gorongosa population at no more than 1,000 birds (38).

On Mt. Mabu (Mozambique), where a population was discovered in 2008, it is assessed to be “fairly frequent” in about 800 ha (8 km2) of forest and with a total population of 100–200 pairs (35), which corresponds to about 300–600 individuals including first-year birds and floaters.

In Zimbabwe it was very common in Chirinda Forest in the 1970s, where it has been suggested it might have occurred at densities of 4 to 6 pairs per ha in optimal habitats (19, 15). It was not uncommon in Bvumba Highlands in the early 1980s (R. Dowsett, in litt. in 20), but was probably less abundant than in Chirinda Forest (19). Since the total area occupied in Zimbabwe was estimated at only 30 km2 in the early 1980s (A. Manson, in litt. in 20), and since habitat in this area is likely smaller today, the Zimbabwe population must be very small.

The population of the nominate subspecies (Zimbabwe and Mozambique populations combined) was considered to be less than 2,000 individuals in 2005 (39), but this estimate does not include the recently discovered population on Mt. Mabu in Mozambique.

S. s. rodgersi (Tanzania)

The population in the Usambara Mountains foothill forests in northeastern Tanzania (26) is believed to be very small (27), but no population estimate is available.

In Udzungwa Mountains it is mostly a low-density species, but is locally common (24, FPJ) with 12.5 pairs/km2 recorded by spot-mapping in Mwanihana Forest (40) and 25 pairs/km2 recorded by territory-mapping at Uhafiwa in southern Uzungwa Scarp (29). The forest area where Swynnerton’s Robin has been recorded in the Udzungwa Mountains covers about 360 km2 (FPJ, unpublished data). Of this, at least 240 km2 is within the species preferred altitudinal range (FPJ, unpublished data). If a conservative estimate assumes 5 pairs/km2 or 15 individuals/km2 when first-year birds and floaters are included, the total Udzungwa population is estimated at 3,600 individuals. It therefore seems likely that the Udzungwa forests contain the species largest population.

Population Regulation

No information.

Recommended Citation

Jensen, F. P. (2022). Swynnerton's Robin (Swynnertonia swynnertoni), version 2.0. In Birds of the World (P. G. Rodewald, Editor). Cornell Lab of Ornithology, Ithaca, NY, USA. https://doi.org/10.2173/bow.swyrob1.02