Response of avian nectarivores to the flowering of Aloe marlothii: a nectar oasis during dry South African winters

Abstract

In southern Africa, Aloe marlothii flowers during the dry winter season and offers copious dilute nectar to a variety of birds. Avian abundance and community composition were monitored at an A. marlothii forest at Suikerbosrand Nature Reserve, South Africa. Sampling occurred during two summer months (February-March) when no flowers were present, and six months (May-October) that spanned the winter flowering. We hypothesized that an influx of occasional nectarivores to the A. marlothii forest during flowering would lead to significant changes in the avian community. Overall bird abundance increased 2-3 fold at the peak of nectar availability (August). We recorded 38 bird species, of 83 species detected during transects, feeding on A. marlothii nectar; this diverse assemblage of birds belonged to 19 families, including Lybiidae, Coliidae, Pycnonotidae, Sylviidae, Cisticolidae, Muscicapidae, Sturnidae, Ploceidae and Fringillidae. Surprisingly, only two species of sunbird (Nectariniidae) were observed feeding on A. marlothii nectar, and both occurred in low abundance. We predicted that competition for nectar resources would be high, but few aggressive inter-and intraspecific interactions occurred between birds while feeding on inflorescences. During peak flowering, insect feeders (insectivores, omnivores, nectarivores) fed on nectar during the cold morning when insect activity was low, whilst non-insect feeders (frugivores and granivores) fed on nectar in the middle of the day. Our study highlights the importance of A. marlothii nectar as a seasonal food and water source for a diverse assemblage of occasional nectarivores.

Evolutionary associations between nectar properties and specificity in bird pollination systems

“…Another suggestion is that low sugar concentrations could discourage robbing of the relatively exposed nectar of GBP flowers, but some of these flowers require secondary compounds to deter insects and sunbirds ( Johnson et al 2006). Occasional nectarivores may visit GBP flowers partly for water (Symes et al 2007): this needs to be tested formally, but we have observed that occasional nectarivores prefer GBP flowers to open water sources. Another related possibility is simply that occasional nectarivores might not discriminate strongly among nectars according to concentration, thus weakening selection for concentrated nectar.…”

“…The first involves sunbirds that are highly specialized nectarivores, and the second involves a variety of occasional nectarivores (Oatley & Skead 1972;Johnson et al 2006;Linder et al 2006;Symes et al 2007). Plants adapted to sunbirds typically rely on a small suite of birds and the birds, in turn, feed mainly on nectar.…”

Sugar preferences and digestive efficiency of the village weaver: a generalist avian pollinator of African plants

“…The village weaver Ploceus cucullatus Müller was studied, as this species and several other closely related weavers are important pollinators of plants with flowers adapted to short-billed generalist avian nectarivores (Oatley and Skead, 1972;Daniels, 1987;Botes et al, 2008;Symes et al, 2008;Brown et al, 2009). Village weavers are predominantly granivores but feed on nectar opportunistically throughout of the year.…”

Stable Isotope Research in Southern African Birds

“…Saguaro provided an important source of nutrients and water for White-winged Doves, whereas for Mourning doves saguaro provided nutrients and less importantly water (Wolf et al, 2002). In South Africa, the importance of sugar in the dilute nectars of A. marlothii has been demonstrated as an important carbohydrate source for numerous opportunistic avian nectarivores (Symes et al, 2008;. In particular the analysis of breath samples has indicated that ingested sugars are used as an income resource for a wide range of opportunistic nectar feeding species .…”