Cooperative Breeding & Sociality in Birds
Cooperative Breeding & Sociality in Birds
Dr Rita Covas (CIBIO, University of Porto and PFIAO, University of Cape Town)
Dr Claire Doutrelant (CEFE-CNRS)
Prof. Ben Hatchwell (‘Nest building' project; Sheffield University)
Kate Carstens (PhD student, PFIAO)
Dr Rob Little (PFIAO)
Dr Martha Nelson-Flower (Postdoctoral Fellow, PFIAO)
Dr Matthieu Paquet (Postdoctoral Fellow, PFIAO)
Dr Andrew Radford (Univ. Bristol, UK)
Margaux Rat (PhD student, PFIAO)
Dr Lizanne Roxburgh (PFIAO Associate)
Dr Doug Schaeffer (PFIAO & Univ California Berkeley)
Dr Robert Simmons (PFIAO Honoroary Research Associate)
Dr René van Dijk ('Nest building’ project; Sheffield University)
Blair Zoghby (MSc student, PFIAO)
Cooperative breeding describes a social system in which animals live in groups, most often comprised of closely related individuals. Within a group, usually only the dominant pair breed, but the other group members (subordinates/helpers) assist in rearing the offspring, despite not being the parents. This creates an apparent conundrum in terms of Darwinian precepts and the search for a unifying theory that explains the evolution of cooperative breeding remains one of the most tantalising holy grails of behavioural ecology. Globally, it is a rare social system – only about 3% of the world’s birds are thought to breed cooperatively (although most of these species are capable, at least under some conditions, of breeding successfully without helpers). Some of these cooperative breeders have been the focus of intense study, often concentrating on the extent to which helpers contribute to group reproductive success. Results of these studies have proved inconclusive in terms of developing a unifying theory to explain the behaviour. In some species, helpers are beneficial to group reproductive performance, yet in others they seemingly confer no benefit or may even be detrimental. The Fitztitute previously embarked on two studies of cooperative breeding in Green Wood-Hoopoes Phoeniculus purpureus and Karoo Scrub-Robins Cercotrichas coryphoeus. Three current, ongoing projects on Southern Ground-Hornbills Bucorvus leadbeateri, Sociable Weavers Philetairus socius and Southern Pied Babblers Turdoides bicolor have, in the last few years, highlighted some key findings regarding the dynamics of cooperative breeding behaviour, its origins and implications for conservation
Southern Ground Hornbill Research and Conservation Project
Research team: Peter Ryan, Rob Little, Kate Carstens & Blair Zoghby
Southern Ground-Hornbills Bucorvus leadbeateri are globally Vulnerable, but their conservation status in South Africa has been up-listed to Endangered. They have experienced a two-thirds reduction in their national area of occupancy, and due to high site fidelity their population size as well, in the past 100 years. They have been on the South African research agenda for decades, mainly thanks to the efforts of Dr Alan Kemp. Since 2000, they have been the focus of a study at the FitzPatrick Institute, UCT, largely to inform activities of the Mabula Ground-Hornbill Project (MGHP) and the national Ground-Hornbill Action Group who are our partners in implementing the national Species Recovery Plan. Our study area is the Associated Private Nature Reserves (APNR) adjacent to the central Kruger National Park.
Co-operatively breeding Southern Ground-Hornbill groups have large spatial requirements, and the APNR supports about 30 groups. We have reproductive histories spanning a decade for more than 20 of these groups. We have been able to show that positive influences on breeding success include group size, the availability of artificial nests, and the amount of open habitat within 3 km of the nest site. A fair amount of information exists, in both South Africa and elsewhere, about the density of ground-hornbill groups, including how many groups exist in a given area. The highest density recorded in southern Africa is one group per 40 km2 at Mana Pools in Zimbabwe. In most places however, including the APNR, densities are much lower at a group per 100 - 250 km2.
There were important aspects of the species’ biology about which we knew very little. These include how big home ranges/territories really are, whether they abut or overlap, and whether seasonal use of home ranges change and is reflected in different seasonal patterns of habitat preference. Trying to answer these questions on the ground by following the birds would take forever and yield less than ideal results because when the birds see an observer, they may change their behaviour. We discovered this fairly early in the project while trying to track the birds ‘on the cheap’ using radio transmitters.
By 2009, we realised that we had to invest in satellite tracking technology. The first satellite transmitter was deployed on a bird in the APNR in February 2010, and since then we have had up to five devices transmitting simultaneously. Each device sends a positional signal once an hour starting before sunrise, while the birds are still on their night-time roosts, until after they return to a roost that evening. We now have more than 25 000 positional fixes, accurate to within a few metres.
During 2011, BSc Honours student William Wyness undertook a preliminary analysis of the satellite data from four ground-hornbill groups, each of which had been tracked for at least a year. This is being continued in more detail by MSc student Blair Zoghby. William’s results suggest that the areas used by different groups across the entire year ranged from 55 km2 up to 103 km2. In the summer breeding season, however, home ranges contracted dramatically. Three of the four groups bred successfully and, during the breeding season these groups used only 24 - 36% of the areas they used in winter. The fourth group attempted to breed, but failed at the chick stage, and ended up using 70% of their winter range during the summer. In summer, there was no overlap between home ranges, in fact, groups never even got close to one another. In winter, however, when groups ranged over much larger areas, there was a small amount of home-range overlap.
We had hypothesised that the boundaries of home ranges may be set by patches of high resource density, as has been shown for foxes. However, this was not the case. Whilst there are some favoured areas that do lie on the edges of home ranges, such hot spots cannot explain the boundaries convincingly. We are fortunate in that a detailed, geo-referenced vegetation map of the study area exists. This allowed William to analyse seasonal patterns of habitat preference in more detail. Despite the large home ranges, the proportions of these that were favoured at any time of year were fairly small (0.5 - 22% across four groups and four seasons). On average, more habitat types were avoided than preferred (2 - 55%), but most habitats were used in proportion to their availability (23 - 98%). The birds were apparently more ‘choosy’ about habitats in the breeding season, but this may be spurious because at this time of year, group members regularly visit the nest to feed either the incubating female or the chick. This central place foraging in summer may merely be an unwillingness of the birds to go too far from the nest. One habitat type that was consistently favoured was open ground. Although open habitats are fairly rare, this may explain why those groups that do have relatively large amounts of open ground close to their nests are the most successful. It also suggests that bush clearance should be used as a management tool to provide optimal sites elsewhere for the placement of artificial nests or for the reintroduction of ground-hornbills. To further inform the reintroduction programme PhD student Kate Carstens is investigating the dispersal behaviour and population structure of subpopulations.
Reintroductions depend on the availability of birds for release which are usually wild stock. Fortunately, ground-hornbills lay two eggs, yet invariably rear only a single chick. The second hatched chicks succumb to dehydration after a few days, having been largely ignored by the incubating female, and are therefore available for harvest and captive rearing allowing reintroduction with no impact on the source population. Since 2010, with permission from the APNR management, we have harvested 17 second-hatched chicks which have been transported by MGHP staff to partner facilities at Loskop Dam, Boscia Birds, Montecasino Bird Gardens and the Johannesburg Zoo where they are reared for the captive breeding and reintroduction programmes. Reintroduction initiatives are already underway at three sites in the Limpopo Province and release techniques for this socially complex species are being refined. We work closely with this initiative which is led and implemented by the MGHP and with the national Ground-Hornbill Action Group.
Thanks to the Department of Science and Technology, the National Research Foundation, the APNR, Dow Southern Africa (Pty) Ltd, the Hans Hoheisen Charitable Trust, Airlink and Senelala Estates for research support. We also thank the Endangered Wildlife Trust’s Large Birds of Prey Programme for assistance with chick harvesting and for recording sightings of our ringed birds.
To help us with data on current populations and breeding sites please send any records of groups and active nesting sites, particularly outside protected areas, to Lucy Kemp at email@example.com. For more information on the Mabula Ground-Hornbill Project visit http://www.ground-hornbill.org.za/. Kate Carstens maintains a Facebook page on the APNR Ground-Hornbill Project at https://www.facebook.com/GroundHornbillResearch.
Pied Babbler Research Project
Research team: Mandy Ridley (team leader), Sabrina Engesser, Margot Oorebeek, Martha Nelson-Flower, James Westrip & Elizabeth Wiley.
Pied Babblers (Turdoides bicolor) are obligate cooperative breeders that live in groups of 3-14 adults which occupy and defend territories year-round. Each group comprises a single dominant breeding pair, and subordinate helpers who assist in rasiing the young produced by the dominant pair. The Pied Babbler Research Project is a long-term research project that was set up by Mandy in 2003. Continuous research and monitoring of the population has continued since then. The study site is based in the southern Kalahari, and researchers conduct observations on fully habituated and ringed groups to ask questions in the areas of behaviour, evolution, and conservation. Our research focusses primarily on the causes and consequences of helping behaviour, parent-offspring conflict, kin recognition, sexual selection, vocal communication and population dynamics. See the Pied Babbler Research Project webpage for more details.
Sociable Weaver Research Project
Research team: Rita Covas (Team Leader), Claire Doutrelant, Matthieu Paquet, René van Dijk & Ben Hatchwell
Sociable weavers Philetairus socius are highly social passerines of the semi-arid savannas of the Kalahari region in southern Africa. They cooperate to build large thatched colonies which they occupy throughout the year. They also cooperate to raise their young, with 30-80% of nests being attended by a group consisting of the breeding pair and 1-5 helpers. We have a long-term study on the sociable weavers at Benfontein Game Farm, near Kimberley, where we investigate fascinating aspects of the species’ cooperative behaviour, life-history and population dynamics. Of particular interest are the benefits and consequences of sociality and cooperation in this species, understanding dispersal patterns and population dynamics, and how cooperation is achieved in colony building. More specific projects currently ongoing are investigating maternal investment in relation to helping and dispersal patterns, the role of dominance and signalling in cooperative behaviour and how the ‘tragedy of the commons’ is avoided in nest building and maintenance. See Sociable Weaver Research Project webpage for more details.