Hartlaub's Gull Chroicocephalus hartlaubii Scientific name definitions

Hartlaub's Gull is a small gull that is endemic to southwestern Africa, where it occurs from central Namibia south to western South Africa. It primarily is found along the coast, but has adapted well to urban areas, and locally occurs up to 50 km inland. Adults of most members of Chroicocephalus have a black, brown, or gray hood during the breeding season; Hartlaub's is a species with at best a very faint gray hood, the head basically appearing white throughout the year. It is named after Gustav Hartlaub, a 19th century German ornithologist.

37–39 cm; 235–340 g; wingspan 89–92 cm. Two-year gull. The breeding adult is white-bodied , with grey mantle ; often with a suggestion of a faint lavender-grey hood with darker border; outer primaries black , with small white windows; bill and legs deep red; eye brown. “Hooded” birds are very like a pale version of L. cirrocephalus, but eye is dark, not white. Non-breeding adult fully white-headed. Juvenile has white head and body, no dark ear spot; back and wings brown, marked with pale buff; tail white, lacking a dark terminal bar. 

• Gray-hooded x Hartlaub's Gull (hybrid) Chroicocephalus cirrocephalus x hartlaubii

Coastal SW Africa, mainly from C Namibia (Swakopmund) to SW South Africa (Dyer I, in SW Western Cape). Has nested exceptionally east to Port Elizabeth, E Cape Province (2 Crawford, R.J.M., Tree, A.J., Whittington, P.A., Visagie, J., Upfold, L., Roxburg, K.J., Martin, A.P. and Dyer, B.M. (2008). Recent distributional changes of seabirds in South Africa: is climate having an impact? African Journal of Marine Science. 30(1): 189–193. Close ).

Coasts, harbours, wet lawns, rubbish dumps and slaughterhouses. Breeds on low, flat islands, including artificial islands and dykes in sewage lagoons and salt-works; sometimes on buildings. Large numbers gather to feed on flooded fields. Does well in urban areas and has spread up to 50km inland around Cape Town. Often feeds at night. (3 Sinclair, I., P. Hockey, W. Tarboton, and P. Ryan (2011). Birds of Southern Africa. Fourth edition. Struik Nature, Cape Town, South Africa. Close ).

Non-migratory. Most ringing recoveries are within 30 km of the ringing site; the longest recovery was 228 km away (4 Anon. (2001). Hartlaub's Gull records. Bull. African Bird Club. 8(1): 6. Close ). Disperses to the mainland coast in both directions; wanders N on Atlantic coast, and rarely E to Natal.

Marine invertebrates, small fish, earthworms, insects, offal and refuse. Much of its natural diet comprises invertebrates, such as kelp fies, associated with stranded kelp Ecklonia maxima and its original distribution is closely correlated with that of kelp (5 Ryan, P.G. (1987). The foraging behavior and breeding seasonality of Hartlaub’s Gull Larus hartlaubii. Cormorant. 15: 23-32. Close ). Occasionally feeds on  flying termites and behind ploughs. Feeds by plunge-diving, swimming, and aerially; also scavenges. On Robben Island eats the eggs of the Swift Terns Thalasseus bergii that nest alongside the gulls and also steals food from them (6 Gaglio, D. and Sherley, R.B. (2014). Nasty neighbourhood: kleptoparasitism and egg predation of Swift Terns by Hartlaub's Gulls. Ornithological Observations. 5: 131–134. Close )

Hartlaub's Gull is quite a vocal species, but its voice is typically considered just 'noisy' and hasn't received much attention, reflected in both lack of voice-specific literature and poor availability of sound recordings.

Vocal Development

No information.

Vocal Array

Kwaaarrr. A loud drawn-out harsh and nasal downslurred kwaaarrr or krrraaah. Note duration ca 0.6‒1.0 s. Uttered at irregular intervals.

Rrreh. A grating nasal short overslurred rreh or krruk, often repeated in series at steady pace. Note duration ca 0.25‒0.5 s. With increasing excitement notes may become longer and louder, evolving into Kwaaarrr type calls.

Squeal. A high-pitched overslurred squeEEeh or wheEEEer. Note duration about 0.5 s, fundamental frequency reaching ca 5‒6kHz.

Other. During courtship feeding, presumably the female utters a klew-klew or crew-crew begging call during bill flicking, often leading to regurgitating food by the male and taken by the female (7 Williams, A. J. (1989) Courtship feeding and copulation by Hartlaub’s Gulls Larus hartlaubii and probable Hartlaub’s Grey-headed Gull L. cirrocephalus hybrids. Cormorant. 17: 73-76. Close ). During copulation, males on their partner's back balance and open their bill uttering a loud, rhythmic kokoko (7 Williams, A. J. (1989) Courtship feeding and copulation by Hartlaub’s Gulls Larus hartlaubii and probable Hartlaub’s Grey-headed Gull L. cirrocephalus hybrids. Cormorant. 17: 73-76. Close ). Alarm call a staccato kekekek or kakakakaka (8 Urban, E. K., C. H. Fry, and S. Keith, Editors (1986). The Birds of Africa. Volume 2. Academic Press, London, UK. Close ).

Geographic variation

No information of any geographic variation.

Phenology

Vocal year-round, but with increased intensity during the breeding season, when breeding colonies may become very noisy places.

Daily Pattern of Vocalizing

Vocal most of the day, without a clear daily cycle. Vocal activity is mainly determined by daily activities, such as keeping contact with group or family members while feeding, alarming against intruders, and breeding activities.

Places of Vocalizing

Vocalizes both from the ground, when swimming, and in flight. Kwaaarrr calls are typically given in flight.

Sex Differences

Little information. Year-round calls presumably uttered by both sexes, but vocalizations described above for female during courtship feeding and male during copulation may be gender-specific.

Social Content and Presumed Functions of Vocalizations

Little information. Rrreh and Kwaaarrr calls are given frequently in various contexts, respectively for normal contact among members of a group and when more alarmed. Squeal is presumably a begging call given by fully grown juvenile birds, both when still in the breeding colony and later on feeding grounds.

None documented.

The breeding season differs between locations. Laying variously listed as February or April to September, or peaking April–June. It begins breeding in November in the north and in January in the south. Breeds throughout year at Swakopmund. Frequently nests with Greater Crested Terns (Thalasseus bergii), and may be displaced by them. Colonies of 10–1000 pairs, with inter-nest distance usually 1–2 m. Prefers bare or slightly vegetated ground. Sometimes nests on roofs. Nest a slight hollow with variable lining material, occasionally 50 cm up on shrubs. Usually 1–3 eggs (1–5, mean 1·8); shell constitutes 11·6% of fresh weight, greater than in almost all other gull species; many eggs lost, replacement clutches having lower survival; incubation c. 25 days; incubating gulls responded to human intrusion at distance of 5 m, returning quickly to nest after intrusion; chick buff with black spots, pale on belly; average hatching weight 28 g, by 5th day 68 g; fledging c. 40 days. Productivity is often very low. First breeding at 3 years. The oldest ringed bird known was 26 years old (9 Demey, R. and Kirwan, G.M. (2003). Africa Round-up: Oldest Hartlaub’s Gull... Bull. African Bird Club. 10(2): 83. Close ).

Not globally threatened (Least Concern). The total population was estimated at around 30,000 birds in 2001 (10 Wetlands International (2015). Waterbird Population Estimates. Wetlands International, Wageningen, The Netherlands. Close ) and has since shown an increasing trend. An earlier estimate, in 1990, estimated the total population at c. 31,000 individuals, based on 12,000 pairs then breeding at 31 localities; at that time it was reported to be declining in Namibia, but increasing in Cape Province, with 28% of the population at Robben Island.

This species has been found to be susceptible to a high rate of breeding failure from both man-induced and natural causes; 60% mortality documented around fledging period, mainly from predation; roof-nesting hazardous, as chicks run off the edge. The main cause of egg mortalityis displacement of incubating gulls by Swift Terns Thalasseus bergii; displaced gulls usually renest, but replacement clutches average smaller and survival lower than in initial nests. On the other hand, on Robben Island the gulls themselves have been found to eat the eggs of Swift Terns and to steal food from them (6 Gaglio, D. and Sherley, R.B. (2014). Nasty neighbourhood: kleptoparasitism and egg predation of Swift Terns by Hartlaub's Gulls. Ornithological Observations. 5: 131–134. Close ).  Kelp Gulls L. dominicanus take eggs, chicks, and occasionally adults; Sacred Ibises Threskiornis aethiopicus and Cattle Egrets Bubulcus ibis eat eggs and chicks. Common Egg-eater Snakes Dasypeltis scabra also target eggs in unguarded nests (11 Underhill, L.G., Sherley, R.B., Dyer, B.M. and Crawford, R.J.M. (2009). Interactions between snakes and seabirds on Robben, Schaapen and Meeuw Islands, Western Cape province, South Africa. Ostrich. 80: 115–118. Close ). Mongooses Herpestes spp. are also major predators.