by Peter Cunningham
Although Grey-backed Sparrow-Lark (Eremopterix verticalis) is encountered throughout the year in the dry southern parts of Namibia, Black- eared Sparrow-Lark (Eremopterix australis) is only observed after good rains. Very little has been published on the nests of both species from Namibia although various authors – e.g. Dean 1997a, Hockey et al. (2005), Keith et al. 1992, Lloyd 1999, Maclean 1970, Maclean 1993, Peacock (2015), Tarboton (2001) – provide nesting details from South Africa.
Nest location
Active searching for nests and serendipitous observations for both species accounted for 30 and 20 nests for Grey-backed and Black- eared Sparrow-Lark, respectively. These data were collected on a farm approximately 70km south of Grünau in southern Namibia between April and July 2020 for Black-eared Sparrow-Lark and August 2019, April and July 2020, for Grey-backed Sparrow-Lark. Most Grey-backed Sparrow-Lark nests were placed alongside a grass species while slightly more nests of Black-eared Sparrow-Lark were alongside a herb and/or shrub. No nests, for either species, were associated with rocks or trees. Hockey et al. (2005) indicates that nests of Grey-backed Sparrow-Lark are usually placed at the base of a grass tuft or dwarf shrub and only occasionally alongside a rock. Peacock (2015) indicates that nests of Black-eared Sparrow-Lark are usually placed next to a bush or tuft while Tarboton (2001) states that most nests are placed against a low shrub, especially Rhigozum trichotomum.
The habitat mostly favoured by Grey- backed Sparrow-Lark for nesting was sandy/gravel plains (70%) compared to Black-eared Sparrow-Lark whose nests were mainly associated with drainage lines (65%). According to Tarboton (2001), Hockey (2005) and Peacock (2015) the nests of both species are associated with various open habitats.
The placement of nests for Grey- backed Sparrow-Lark were mostly associated with grasses Stipagrostis fastigiata (n = 8), Stipagrostis ciliata (n = 5) and Stipagrostis uniplumis (n = 5) while Black-eared Sparrow-Lark selected Stipagrostis fastigiata (n = 5) and Rhigozum trichotomum (n = 4). Although both species nested alongside a variety of plant species, Grey-backed Sparrow-Lark was associated with more species – i.e. 12 versus 9 species. Grey-backed Sparrow-Lark nests were associated with grasses (63.3%) compared to Black-eared Sparrow-Lark with herbs and shrubs (55%). Tarboton (2001) confirms low shrubs, especially Rhigozum trichotomum, selected by Black-eared Sparrow- Lark while none of the authors provide species specifics for Grey- backed Sparrow-Larks.
The majority of nests were located on the southern side of vegetation for Grey-backed (83.3%) and Black-eared Sparrow-Lark (85%) with most nests located to the south and southeast (73.3%) for Grey-backed Sparrow- Lark and to the south (50%) for Black-eared Sparrow-Lark.
This is probably done for thermoregulation purposes. Tarboton (2001) and Hockey et al. (2005) indicate that most nests for both species are located in the shade – i.e. to the south and east. Although not assessed during this study, an interesting question is the advantage shrub nesters may have over bunchgrass nesters in moderating thermoregulation, as a nest placement strategy, as indicated by Wells & Fuhlendorf (2005) for some species of grassland ground nesting birds in the USA.
Nest concealment
To determine the visibility of the nests, I viewed the nests from directly above and allocated % cover classes as 25, 50, 75 & 100%, respectively. Although nests for both species are well concealed from above, Grey- backed Sparrow-Lark nests (66.7 ± 6.03%; SE) are less concealed than Black-eared Sparrow-Lark nests (80 ± 6.2%; SE). Better concealed nests are probably to avoid avian predators. Pied Crows were often seen flying low and landing in the veld and although not confirmed, probably predated on eggs and/or chicks.
Nest construction
Except for one Grey-backed Sparrow- Lark nest with some fine plant roots included in the nest cup, all the other nests were constructed entirely of Stipagrostis spp. inflorescence. Black-eared Sparrow-Lark nest cups were similarly constructed of Stipagrostis spp. inflorescence, although two nests had some twigs and one nest had twigs and rootlets included. No animal hair, feathers or wool was observed in the nest cups encountered. Tarboton (2001) confirms the use of grass inflorescence by both species, although plant down (e.g. Eriocephalus spp.; Keith et al. 1992) and wool is also used as nesting material by Grey-backed Sparrow- Lark. The nests of both species are lined with the awns of Stipagrostis spp. grasses (especially S. ciliata) (Dean 1997b). Black-eared Sparrow- Lark also includes other plant petioles (Tarboton 2001) and rootlets (Maclean 1970). Similar to other authors (e.g. Hockey et al. 2005, Peacock 2015, Tarboton 2001) the nests of Grey-backed Sparrow-Lark observed were surrounded by a pebble pavement (70% of nests); combination of pebbles and twigs (16.7% of nests); twigs only (3.3%) on in some case no pavement at all (10% of nests). On the other hand all the Black-eared Sparrow-Lark nests observed had a pavement of twigs and rootlets covered by buck-spoor spider web (Seothyra spp.), something viewed as consistent with the nests for this species (Tarboton 2001). This sand encrusted silk flap which resembles a hoofprint (i.e. buck-spoor) in the sand, serves as a signal web at the entrance to the spider’s burrow (Dippenaar- Schoeman 2014). This web used by the Black-eared Sparrow-Lark to cover the twigs around the cup of the nest probably assist with the camouflage of the nest as they blended into their surroundings well and were usually difficult to locate.
Nest dimensions
Grey-backed Sparrow-Lark:
According to Keith et al. (1992) and Tarboton (2001), nests have a cup diameter of 54 mm and a cup depth of 30 mm; while Tarboton (2001) indicates that a pebble pavement (i.e. outer nest dimension) could extend another 100 mm beyond the rim of the nest. My data (n = 30) indicate the cup diameter being 52.3 ± 1.2 mm; cup depth being 33.7 ± 0.9 mm and total nest diameter, including pebble pavement, being 118.9 ± 5.6 mm. Except for the smaller pebble pavement, all other nest measurements are similar to that presented by Tarboton (2001). It is postulated that the smaller pebble pavements observed during this study are probably as a result of the open, more sparsely vegetated habitat in southern Namibia – i.e. larger pebble pavements would extend beyond the grass/shrub and thus make the nest more visible to avian predators.
Black-eared Sparrow-Lark:
According to Maclean (1970) and Tarboton (2001), nests have a cup diameter of 52 mm and a cup depth of 33 mm; while Tarboton (2001) indicates that an outer spider web encrusted rim (i.e. outer nest dimensions) could extend another 50 mm beyond the rim of the nest. My data (n = 20) indicate the cup diameter being 52.9 ± 1.1 mm; cup depth being 36.7 ± 1.2 mm and total nest diameter, including web encrusted twig rim, being 102.1 ± 2.6 mm. All nest measurements are similar to that presented by Maclean (1970) and Tarboton (2001).
Egg laying months
Grey-backed Sparrow-Lark:
Egg laying occurs during all months and opportunistically especially in response to rainfall events between 20-30 mm although between 40-50 mm is required for extensive breeding as well as sufficient grass growth (Lloyd 1999, Maclean 1970, Tarboton 2001). Data from Namibia (n = 116) indicate that egg laying occurs throughout the year although no nesting data exists for July, September to November (Brown n.d.). Of the 7 nests I encountered with eggs/chicks present, 5 nests were found during April (2 with eggs and 3 with chicks) and 2 nests during May 2020 (1 with eggs and chicks each). According to Brown (n.d.) 62.1% (n = 116) of the nesting records from Namibia are associated with April and May. This coincides with the main rainfall associated between February and April in southern Namibia – e.g. over 90 mm measured on farm between February and April 2020.
Black-eared Sparrow-Lark:
Egg laying occurs during all months and opportunistically especially in response to rainfall although requires between 40-50 mm to stimulate extensive breeding (Dean 1997a, Lloyd 1998, Maclean 1970, Tarboton 2001). Data from Namibia (n = 8) indicate that egg laying occurs during April (Brown n.d.). Of the 10 nests I encountered with eggs/chicks present, 6 nests were found during April (3 with eggs and chicks each) and 4 nests during May 2020 (all 4 nests with eggs). According to Brown (n.d.) 100% (n = 8) of the nesting records from Namibia are associated with April. This coincides with the main rainfall associated between February and April in southern Namibia – e.g. over 90 mm measured on farm between February and April 2020.
Clutch size
Grey-backed Sparrow-Lark:
Clutch size is usually 2 eggs (1-3 and rarely 5) (Tarboton 2001, Peacock 2015) or 2.6 eggs (mode of 3; n = 338) (Lloyd 1999) with egg colour indicated as being dull white speckled with yellowish brown, brown and grey marking concentrated at the obtuse end (Tarboton 2001). Data from Namibia indicate a clutch size of 2.2 eggs (n = 74) (Brown n.d.). My data (n = 7) indicate that both nests with eggs and/or chicks present had a mean of 2.43 ± 0.2 eggs/chicks with the colour being similar to that indicated by Tarboton (2001) (Figures 6&8). Eggsizesare19x14mm (Tarboton 2001) or 16.9-21.4 x 12.3- 16.4 mm (n = 363) (Maclean 1993). Data from Namibia indicate egg size of 18.2-21.4 x 13.1-16.4 mm (n = 52) (Brown n.d.). My data (n = 6) indicate eggs size of 18.5-21.5 (20.3 ± 0.6 mm) x 13.0-16.0 mm (14.2 ± 0.6 mm). Clutch and egg sizes are similar to other above mentioned author’s data.
Black-eared Sparrow-Lark:
Clutch size is usually 2 eggs (1-3 and rarely 4) (Tarboton 2001, Peacock 2015) or 2.54 eggs (mode of 3; n = 148) (Lloyd 1999) with egg colour indicated as being white speckled with pinkish brown marking concentrated at the obtuse end (Tarboton 2001). Data from Namibia indicate a clutch size of 1.5 eggs (n = 8) (Brown n.d.). My data (n = 10) indicate that both nests with eggs and/or chicks present had a mean of 2.3 ± 0.2 eggs/chicks with the colour being similar to that indicated by Tarboton (2001) (Figures 7 & 9). Egg sizes are 16.7-20.6 x 12.3-14.9 mm (n = 103) (Keith et al. 1992). There is currently no data from Namibia (Brown n.d.). My data (n = 16) indicate eggs size of 16.8-20 mm (18.1 ± 0.2 mm) x 13-14.5 (13.7 ± 0.1 mm). Clutch and egg sizes are similar to other above mentioned authors’ data.
Although most of my nesting data of Grey-backed and Black-eared Sparrow-Lark from southern Namibia are similar to those published by other authors from South Africa, these data nevertheless increase our knowledge of species often overlooked and/or taken for granted throughout their range. New data include plant species selected as nesting sites for both species and nesting habitat, egg laying months and egg measurements for black-eared sparrow-lark from Namibia.
As Grey-backed and Black-eared Sparrow-Lark breeding is associated with rainfall events, especially events equalling and/or exceeding 40-50 mm, coupled with suitable grassgrowth required for nesting, they are potentially species negatively influenced by climate change issues such as fluctuating rainfall events. Furthermore, Black-eared Sparrow- Lark may also be affected by overgrazing (Del Hoyo et al. 2004),which in turn will be exacerbated by variable rainfall events. Although, probably viewed as insignificant now, the presence/absence of breeding of these small sparrow-larks may be indicative of local climate change phenomena.
Brown, C.J. n.d. (accessed on 14-04- 2020). Breeding data on the birds of Namibia.