Hartlaub's Francolin
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[Photo] Hartlaub's Francolin (Francolinus hartlaubi). Joris Komen.

The Hartlaub's Francolin, Francolinus hartlaubi is an endemic bird species of the escarpment zone of Namibia and Angola. Its name commemorates the German zoologist Gustav Hartlaub.

Identification

Appearance
A small, squat bird; both sexes of this species have disproportionately large bills for their size (in comparison to other Francolin species). The bare parts are mostly a dull yellow; the large bill is a brownish yellow.

Male: Strong contrast of mottled buff/brown upperparts and white underparts streaked with brown. Black forehead with white eyebrow conspicuous. Black-and-white barred undertail coverts especially diagnostic in flight. Female: Like male, but with cinnamon (not white) unstreaked underparts, grey-brown head and orange-brown eyebrow. Lacks undertail barring of male. Juvenile: Buffy forehead and brown crown tinged with rufous. Upperparts buffy grey with black and white vermiculations. Breast barred black and white, with buffy grey belly

Measurements
Length: Male 28cm (11 in) Female 25cm (10 in).
Weight: 210-290g (~0.5-0.63 lb); the male is heavier than the female.

Distribution and habitat

Distribution and status
Hartlaub's Francolin is endemic to southwest Africa, occurring only in northcentral to northwestern Namibia and a small area of southwestern Angola. It is not especially common throughout its limited range. The Namibian population is estimated at c. 26 000 birds. However, this bird's conservation status is not threatened, probably because its habitat is of little commercial value to humans at this stage. Granite mining activities are a potential threat to their habitat. Though Francolins are a gamebird, Hartlaub's is too small to be of any special culinary value.

Habitat
Hartlaub's Francolin is an inhabitant of medium-altitude arid and semi-arid regions from 800-1600m (2600-5200 ft). Throughout its range its preferred habitat consists of higher ground, mostly on rocky granite and sandstone outcrops (popularly known as "koppies" to locals), surrounded by semi-desert steppe. There is invariably relatively dense grass and shrubbery associated with these outcrops.

Behaviour and diet
Habitat use, foraging behaviour and diet of male and female Hartlaub's Francolin are related to the availability of corms, seed and insects of different sizes in different habitats. Hartlaub's Francolin primarily forage on granitic outcrops, and use a variety of feeding techniques, with significant sexual differences in foraging behaviour and, to a lesser degree, dietary composition.

Males consume a greater diversity of food items than females, although there is considerable dietary overlap between the sexes, and sexual differences in feeding techniques result in some food items being prioritized by each sex. In particular, distinct functional differences results from females' almost exclusive digging habits, in contrast to males' wider range of foraging techniques, including an apparently male-specific foraging technique of exposing cryptic termites.

The relatively larger-billed females specializes on digging out the corms of Cyperus sp which, within the species, appears to be primarily carried out by females, with males spending proportionally more time foraging for a more diverse diet of insects and seed. It is hypothesized that this sexual difference in diet is adaptive, in response to predator and sexual selection pressures. The relatively narrow dietary spectrum of female Hartlaub's Francolins may be a causative factor in vigorous perrenial defence of territorial resources.

Hartlaub's Francolins occur in pairs or small family parties of 3-4 and are inconspicuous unless calling. They are not easily flushed, preferring to hide between boulders. Flushed birds will utter a rapid, chattering 'krak', flying rapidly.

Red-billed Francolin and Orange River Francolin occur alongside this species, but they occupy different habitats. The Red-billed Francolin prefers bush along watercourses and Orange River Francolin can be found on the slopes leading up to the rocky outcrops occupied by the Hartlaub's Francolin .

Breeding habits
Hartlaub's Francolins appear to be perennially territorial, with variable numbers of boundary call sites demarking each territory. Call-sites are used by territorial pairs on a regular basis, for daily bouts of antiphonal duets. The frequency of use of particular call-sites appears to be influenced more by the presence (vocalizations) of un-mated females on particular boundaries, than by the daily duetting of neighbouring pairs. The mean territory size of Hartlaub's Francolin pairs is 40863.9±12016.1 square metres (n = 12 pairs). Dependent on annual breeding success and offspring survival, the mean population density of the study area during 1983 through 1989 ranged from one bird in 0.82 ha to one bird in 2.04 ha, with an average annual population density of one bird in 1.43 ha. There was no significant difference in outer convex polygon areas determined by call sites and radio-telemetry. However, core ranges and utilization distributions of pairs, and, in particular, the multiple nuclei of different daily activities could only be distinguished by radio-telemetry. The 90% multiple nuclei of seasonal distribution are correlated with patchy distribution of food resources favoured by females, and, whilst rearing young, the distribution of insects, and especially cryptic termites.

Antiphonal duets of territorial pairs are audibly distinguishable, on the basis of temporal and structural differences in the female vocal elements of duets. Territorial pairs use antiphonal duets on a daily basis to advertise their presence, and such calling was most frequent shortly after sunrise. Un-mated females call far more frequently than territorial pairs, often throughout the day, with peaks at shortly after sunrise and before sunset. Playback experiments with the advertising calls of un-mated females within territory boundaries of established pairs, elicited vigorous vocal and behavioural responses from territorial females. Male calls are more conservative than female calls, with females using a wider repertoire of vocalizations.

The mating system of Hartlaub's Francolin can be described as a female dominated resource defence monogamy. Perrenial territorial resources (food, traditional call-sites, refuge and suitable nest-sites) are primarily defended by female Hartlaub's Francolins. By excluding other females from the vicinity of the resource, the defending female can count on male visitation, life-mating and thus biased mating access with guaranteed fertilization. The pair bond is maintained by ritualised behaviours, including pair-distinct (female initiated) antiphonal duetting and reverse mounting during courtship and incubation. Operational sex ratios are "female skewed" and probably strongly influenced by predation, with noticeably large numbers of strongly- vocal female 'floaters' and a virtual absence of un-mated males. It is unusual that this sex-role reversed monogamy occurs in a species which is strongly sexually dichromatic and dimorphic, with the males more brightly coloured and somewhat larger than females.

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