Breeding success and population growth of Southern Ground Hornbills Bucorvus leadbeateri in an area supplemented with nest-boxes

Abstract

SummaryThe provision of artificial nests can improve the conservation status of threatened bird species that are limited by nest-site availability. The shortage of natural cavity nesting sites is one factor limiting the population growth of the Southern Ground Hornbill Bucorvus leadbeateri. In an 1,800 km2 study area in north-eastern South Africa, 31 wooden nest-boxes were installed during 2002–2015. We investigated the relationships between nests, as well as environmental and social factors, with breeding. Generalised linear mixed models were fitted to the observational data and identified positive relationships between breeding attempts and each of home range size and the previous year’s rainfall; as well as positive relationships between breeding success (amongst the groups that attempt breeding) and each of earlier breeding, nest height and thickness of the nest cavity wall. The provision of nest-boxes increased the number of breeding groups and although breeding success also increased initially, it later declined as the density of breeding groups increased above 20 groups. Although nest-boxes alone did not increase overall breeding success, they are an effective conservation tool to enhance the population of Southern Ground Hornbills if spaced optimally, to enhance reproductive output in areas where suitable nest-sites are scarce or lacking.

Review of trial reintroductions of the long-lived, cooperative breeding Southern Ground-hornbill

“…No impact or reduction in viability of source populations has been found following the removal of redundant second-hatched chicks (Carstens et al 2019a), supporting the 'insurance' hypothesis for obligate brood reduction (Morandini and Ferrer 2014). These chicks, despite captive rearing, were able to function as founder and mentor stock, bred successfully and reared a new generation, provided that behavioural factors were adequately addressed, and that the reintroduction happened during the rainy season.…”

Avian Behavioral and Physiological Responses to Challenging Thermal Environments and Extreme Weather Events

“…Additionally, significantly more breeding attempts succeeded (fledged at least one chick) in nondrought seasons (61.5%) compared to drought seasons (17.4%). The near-ubiquitous nest failure across a range of T air in drought years presumably occurred because low rainfall leads to low food abundance in arid and semi-arid systems since rainfall drives primary productivity and the energy available through the entire trophic cascade (Mares et al, 2017;Carstens et al, 2019). These results suggest that breeding performance in this population of hornbill is susceptible to both low rainfall and high T air independently, compared to studies suggesting vulnerability only when low rainfall and high T air co-occur (Flesch, 2014;Cruz-McDonnell and Wolf, 2016;Bourne et al, 2020b).…”

“…Possible consequences for animals inhabiting arid regions include increased frequency of mass mortality events and disastrous reproductive failures (Bolger et al, 2005;Seabrook et al, 2014;. However, heatwaves, especially in association with droughts, may also have insidious sublethal effects Bourne et al, 2020b, including loss of body condition , reduced egg or clutch sizes in birds Keynan and Yosef, 2010), reduced provisioning rates and compromised offspring quality (van de Ven et al, 2020a;, and the foregoing of breeding altogether (Moreno and Møller, 2011;McCreedy and van Riper, 2015;Carstens et al, 2019).…”

Killing with kindness: Does widespread generalised provisioning of wildlife help or hinder biodiversity conservation efforts?

“…Replacement feeding for vultures which have lost natural resources due to human activity, and to steer them away from contaminated food, is also allowing threatened populations to persist (Cortés-Avizanda et al, 2016). Additional feeding of several threatened species under population management programs has allowed them to expand and/or recolonise former ranges, conferring greater resistance to stochastic events (Clout et al, 2002;González et al, 2006), as has nestbox provision (Carstens et al, 2019). Reintroductions of species of conservation concern often rely on initial additional resource provisioning to encourage population persistence (Cortés-Avizanda et al, 2016;Piper et al, 1999).…”