Box 5.1 Invasive Common Starlings and Common Mynas
Both Common Starlings Sturnus vulgaris, and Common Mynas, Sturnus
tristis have not fully exploited their potential niches in southern Africa and
are still expanding eastwards and northwards. Of the estimated 2.38 billion
birds and 3.87 million on average per species for the region, the two invasive
starlings (Common Starling: 3.15 million; Common Myna: 1.08 million) are
comparable with the average of 2.52 million each of the 14 native Sturnidae
species (Hui et al. 2009). Sturnidae species are medium sized, c. 100 g, and
highly detectable due to their conspicuous features and flocking behaviours.
Both species are dietary generalists and commonly occur in urban areas and
farms, with no feasible control measures planned. Common starlings are often
seen with Pied Starlings (Spreo bicolor) and Wattled Starlings (Creatophora
cinerea) in mixed flocks; in contrast, Common Mynas are bold and particularly aggressive during feeding and roosting (Hockey et al. 2005).
A number of studies have explored the population genetics, dispersal
strategies and morphological traits of both species during their range expansion in the region (Berthouly-Salazar et al. 2012a, b, 2013; Hui et al. 2012;
Phair et al. 2018). In particular, the invasion dynamics of the two species have
supported the two contending mechanisms behind boosted/accelerating invasive range expansion (Hui and Richardson 2017): frequent long distance
dispersal (LDD) and spatial sorting. Frequent LDDs are often captured by a
leptokurtic fat-tailed dispersal kernel (Kot et al. 1996; Ramanantoanina et al.
2014), whilst spatial sorting of individuals with stronger dispersal abilities at
the advancing range edge could leave behind a shift of dispersal-related traits
from the introduction point to the range front (Shine et al. 2011). The coreedge comparison of morphological traits for Common Starlings sampled
across South Africa shows little signs of spatial sorting of wing morphology,
but instead reveals associations of resource competition traits (bill morphology) with distance to the introduction location (Phair et al. 2018). This is
similar to the pattern of Common Starlings in North America (Bitton and
Graham 2015) but contrasts with detected spatial sorting of wing morphology
in Australia (Phair et al. 2018). Genetic analyses of Common Starlings in
South Africa have confirmed strong genetic connectivity between core and
edge populations, supporting frequent LDDs behind boosted range expansion
(Berthouly-Salazar et al. 2013). The acceleration of range expansion of Common Starlings in South Africa is linked to increased contact with changing
precipitation regimes (Berthouly-Salazar et al. 2013), supporting the “good
stay, bad disperse” rule identified for Common Starlings in Britain (Hui et al.
2012). The detected spatial sorting of bill morphology reflects altered selection
forces imposed by different environmental heterogeneity (Phair et al. 2018),
also pointing out potential trade-offs between dispersal and foraging traits that
could offset the pattern of spatial sorting of dispersal traits (Brown et al. 2013).
(continued)
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Both Common Starlings Sturnus vulgaris, and Common Mynas, Sturnus
tristis have not fully exploited their potential niches in southern Africa and
are still expanding eastwards and northwards. Of the estimated 2.38 billion
birds and 3.87 million on average per species for the region, the two invasive
starlings (Common Starling: 3.15 million; Common Myna: 1.08 million) are
comparable with the average of 2.52 million each of the 14 native Sturnidae
species (Hui et al. 2009). Sturnidae species are medium sized, c. 100 g, and
highly detectable due to their conspicuous features and flocking behaviours.
Both species are dietary generalists and commonly occur in urban areas and
farms, with no feasible control measures planned. Common starlings are often
seen with Pied Starlings (Spreo bicolor) and Wattled Starlings (Creatophora
cinerea) in mixed flocks; in contrast, Common Mynas are bold and particularly aggressive during feeding and roosting (Hockey et al. 2005).
A number of studies have explored the population genetics, dispersal
strategies and morphological traits of both species during their range expansion in the region (Berthouly-Salazar et al. 2012a, b, 2013; Hui et al. 2012;
Phair et al. 2018). In particular, the invasion dynamics of the two species have
supported the two contending mechanisms behind boosted/accelerating invasive range expansion (Hui and Richardson 2017): frequent long distance
dispersal (LDD) and spatial sorting. Frequent LDDs are often captured by a
leptokurtic fat-tailed dispersal kernel (Kot et al. 1996; Ramanantoanina et al.
2014), whilst spatial sorting of individuals with stronger dispersal abilities at
the advancing range edge could leave behind a shift of dispersal-related traits
from the introduction point to the range front (Shine et al. 2011). The coreedge comparison of morphological traits for Common Starlings sampled
across South Africa shows little signs of spatial sorting of wing morphology,
but instead reveals associations of resource competition traits (bill morphology) with distance to the introduction location (Phair et al. 2018). This is
similar to the pattern of Common Starlings in North America (Bitton and
Graham 2015) but contrasts with detected spatial sorting of wing morphology
in Australia (Phair et al. 2018). Genetic analyses of Common Starlings in
South Africa have confirmed strong genetic connectivity between core and
edge populations, supporting frequent LDDs behind boosted range expansion
(Berthouly-Salazar et al. 2013). The acceleration of range expansion of Common Starlings in South Africa is linked to increased contact with changing
precipitation regimes (Berthouly-Salazar et al. 2013), supporting the “good
stay, bad disperse” rule identified for Common Starlings in Britain (Hui et al.
2012). The detected spatial sorting of bill morphology reflects altered selection
forces imposed by different environmental heterogeneity (Phair et al. 2018),
also pointing out potential trade-offs between dispersal and foraging traits that
could offset the pattern of spatial sorting of dispersal traits (Brown et al. 2013).
(continued)
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J. Measey et al.