An investigation to determine the critical habitat requirements of the breeding Blue Swallow Hirundo atrocaerulea Sundevall.

Abstract

This study investigated the critical habitat requirements of breeding Blue Swallows Hirundo atrocaerulea Sundevall, in KwaZulu-Natal, South Africa. Blue Swallows, as a 'flagship species' of the KwaZulu-Natal endemic Mistbelt Grassland, were tagged and radio-tracked to obtain positional data to determine their habitat use while breeding. This information was correlated to the type and nature of the habitat used and to the nature of the land cover to determine the likely impact of habitat transformation and fragmentation on breeding Blue Swallows. Insect type and abundance was assessed in five surrounding habitat types using Malaise insect traps and the findings correlated to Blue Swallow habitat usage. Data on environmental variables were collected using HOBO® sensors and the findings related to insect type and abundance within each habitat type. A comparative investigation was undertaken using temperature and humidity data obtained below-ground at a Blue Swallow nest site and compared to temperature and humidity findings from above-ground. Preliminary investigations were also made into the breeding system used by the Blue Swallow using unique wing markings to estimate the number of individuals involved at a single active nest. Overall, wetland and grassland were first choice habitats a function of the increased individual insect mass in these habitats. Tea plantations were the next most important habitat type and timber plantations were avoided. Furthermore, it was shown that the Blue Swallow is a species that favours ecotones as preferential forage zones, particularly the ecotone between wetland and grassland. Malaise insect traps were effective in gathering suitable insect samples for analysis, revealing that significant differences occur in insect order, number and mass between habitat types. The most significant finding is that average insect mass per order, which was correlated closely to habitat type, matches the order of positive habitat type selection by the Blue Swallow. These findings were statistically significant and it is suggested that this correlation is the main reason behind the habitat selection by Blue Swallows. This study found a clear indication that insect numbers and mass, in grassland and wetland, increase with an increase in temperature and decrease with a decrease in average temperature. Clear trends were obvious during long periods of either cold or dry weather which .negatively influenced insect abundance and potentially, in turn, Blue Swallow well-being. The underground cavity used as the nesting site by Blue Swallows, experiences a greatly moderated climate in terms of the range of environmental factors compared with those experienced above-ground. This climate moderation is thought to be a clear advantage for the well-being of the Blue Swallow eggs and nestlings. Through the use of radio-tracking, visual markers and video footage it was clear that Blue Swallows breed with a number of adult birds at one nest. The recorded average sex ratio was 1(; : 3<;2, however, the need remains to elucidate the co-operative breeding system used by the Blue Swallow. In conclusion, the findings of this work present recommendations and suggestions on habitat management, offer insight into future research opportunities, and suggest strong conservation action for the species.