by Peter Cunningham (Snr), Peter Cunningham (Jnr) and Janke Cunningham
We present some data on seventeen Namaqua Sandgrouse (Pterocles namaqua) nests serendipitously encountered on a farm located roughly midway between Grünau and Noordoewer in southern Namibia.
Habitat
According to various authors Namaqua Sandgrouse breeds on “flat, open ground, mostly on calcrete, sand or on shingle/gravel plains” (Tarboton 2001); “sparsely vegetated calcrete and sandy flats” (Little and Crowe 2011); “within a local concentration of low objects” (Lloyd et al. 2000) or “generally in exposed situations, but within a local concentration of objects, most of them <15cm high and concentrated within 30cm of the nest” (Lloyd et al. 2001).
This study:
The farm is located within the dwarf shrub savanna (Giess 1971) or Karas dwarf shrubland (Mendelsohn et al. 2002) vegetation type – i.e. Nama Karoo – with sparse shrubland being the dominant vegetation structure. Slightly more nests were associated with small ephemeral drainage lines, either located within the drainage line (n = 3 nests) or on the edge thereof (n = 6 nests) than on sandy/gravel plains (52.9% versus 47.1%) (Table 1). As the drainage lines typically have denser vegetation in the general area, these nest site selections probably indicate the increased camouflage value of this habitat type.Nests were associated with – i.e. in close proximity to – a wide range of vegetation although Stipagrostis fastigiata (n = 5 nests) and Rhigosum trichotomum (n = 4 nests), speciestypically associated with ephemeral drainage lines throughout the area, were species often favoured (Table 2). S. uniplumis is the dominant grass in the area.
Nest
According to Hockey et al. (2005) the nest is a simple scrape in the ground usually exposed to the elements or placed “next to” a natural feature such as a couple of stones or a tuft of grass (Little and Crowe 2011) while Tarboton (2001) states that nests are usually not set right against a stone or bush. Lloyd et al. (2001) indicates that most nests are located close to various objects (within 30cm of the nest) which may serve as disruptive camouflage or serve as concealment of the incubating bird (Lloyd et al. 2000).
This study:
The mean average distance between the nests and the nearest perennial grass and nearest herb/shrub/tree was 41.1±12.2cm and 51.3±14.5cm, respectively (Table 3). This study indicates that nests are not usually located “next to” a natural feature as indicated by Little and Crowe (2011)and slightly further than 30cm as indicated by Lloyd et al. (2001), but rather in accordance with Tarboton’s findings (2001). However, 5 nests (29.4%) were located within 1cm of perennial vegetation – i.e. directly against and/or under such vegetation (Figures 1a to 1c).Why nests were placed below vegetation is unclear and probably not for shade purposes as the nests were all located during the cooler months (i.e. June [n = 1]; July [n = 12] & August [n = 4]), but probably rather to avoid predators. Lloyd et al. (2000) indicated that mammalian predators accounted for most of their predated nests and that avian predators are not viewed as important predators. However, placing nests below shrubs, as encountered for 29.4% of the nests during this study, probably indicates an attempt at avoiding avian predators. Pied Crow and Southern Pale Chanting Goshawk have a constant presence in the area with Lanner Falcon and Booted Eagle also occasionally observed. These birds are known predators of Namaqua Sandgrouse and/or their eggs (e.g. Hockey et al. 2005). Only three nests were located close to rocks during this study (17.6%) and probably reflect more on the general habitat rather than structures selected for nesting as suggested by Lloyd et al. (2000).
Nesting material
Nests are usually unlined, although some may have a rim of pebbles (Tarboton 2001) while Maclean (1968) states that the nest may become filled with grit and plant matter during the incubation period.
This study:
Of the 17 nests we encountered, only one nest (5.9%) had no ‘nesting material’ present while other material encountered in the nests included small stones (41.2%), grass remains (58.8%), twigs from shrubs (35.3%), faeces from sheep/springbok (29.4%) and Tribulus terrestris seeds (17.6% ) (Table 1). None of the nests we encountered had a rim of pebbles while the ‘nesting material’ – detritus – observed may have blown into the nest and/or against the incubating bird and become so embedded as nesting material. However, this does not account for the 41.2% of the nests with pebbles therein – i.e. material too heavy to be blown into the nest. Furthermore, the nesting material seemed orderly placed rather than randomly included as windblown detritus (Figures 1b & c; 2 & 3). Another interesting observation seemed like bill scrape marks located on the edge of some nests potentially indicating the incubating bird actively collecting passing detritus to be included within the nest (Figure 2). It is thus probable that windblown material collects passively in the nests, although the heavier material (pebbles – Figure 3) together with the bill scrape marks suggests that some active collection of nesting material potentially takes place.
Nest dimensions
The nest scrape is 100-110 mm in diameter and 20-30mm deep (Tarboton 2001).
This study:
Our nest data indicate a diameter of 13.9±0.4cm and depth of 1.9±0.1cm (n = 17 nests; Table 3) – i.e. slightly larger and shallower than presented by Tarboton (2001). This probably depends on the substrate – e.g. sandy areas have bigger nests than on harder surfaces – or differences in determining the actual outer rim of a nest without a typical border.
Eggs
The clutch is usually 3 eggs, rarely 2 (Tarboton 2001) with a mode of 3 eggs (2.88; n = 256 complete clutches) (Lloyd et al. 2001).
This study:
The mean average number of eggs we encountered was 2.19±0.3 eggs per nest (range 1-3; n = 17 nests; Table 3), although we did not revisit all nests to confirm if these were complete clutches. One nest (Nest No 14; Table 3) had 2 eggs on 1/8/2018 and again on 14/8/2018 indicating that this was a completed clutch of 2 eggs. Eggs in three of the nests we encountered had recently hatched as was evident from partial egg shells in the nest and immediate vicinity. We also encountered 2 single eggs (both cold – abandoned) not associated with a nest probably indicating some birds laying eggs although not for breeding purposes and/or disturbed at the onset of laying (this data was not included in our analyses).
Laying season
Eggs can be laid throughout the year, but mainly between July and August throughout most of its range (Tarboton 2001) or April to July in the southern Namib and August to January in the Nama Karoo (Lloyd et al. 2001) while Little and Crowe (2011) indicate that although strongly variable, the Namibian populations breed from late summer into the winter (January to August with a peak in May).
This study:
Our breeding records are in accordance with other authors (See above). Although birds are observed throughout the year, we only encountered nests during June, July and August during this study – i.e. cooler winter months. Chicks wereobserved during June 2018 (3 chicks each on 2 occasions). During 2018 we had late rains – between 23 and 30mm during late March – resulting in good grass growth, probably resulting in associated breeding as no nests were encountered during previous years (2015-2017) with below average rainfall.
Giess, W. 1971. A preliminary vegetation map of South West Africa. Dinteria 4: 1 – 114.
Maclean, G.L. 1968. Field studies on the sandgrouse of the Kalahari Desert. Living Bird 7: 209-235.
Mendelsohn, J., Jarvis, A., Roberts, A. & Robertson, T. 2002. Atlas of Namibia. A portrait of the land and its people. David Philip Publishers, Cape Town, RSA.