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Providing evidence to improve practice

Action: Provide supplementary food for nectar-feeding songbirds to increase adult survival Bird Conservation

Key messages

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  • Two studies from Australia and New Zealand found that ten species of honeyeaters and stitchbirds Notiomystis cincta readily used feeders supplying sugar solutions, with seasonal variations varying between species and stitchbirds spending more time foraging for insects when food was supplied.
  • A series of ex situ trials using southern African birds found that most species tested showed a preference for sucrose solutions over glucose or fructose. One study found that sunbirds and sugarbirds only showed such a preference at low (equimolar) concentrations. Two more studies found that two species showed preferences for sucrose when comparing 20% (by weight) solutions, although a third species did not show this preference. All species rejected solutions with xylose (a natural sugar in nectar) added. A final study found that sucrose preferences only became apparent at equicalorific concentrations high enough for birds to subsist on.

 

Supporting evidence from individual studies

1 

A replicated study on heathland in New South Wales, Australia in 1986-8 (Armstrong 1992) found that ten species of honeyeater were observed using supplementary feeders over 129 hours of observation. The most common were New Holland honeyeaters Phylidonyris novaehollandiae, white-cheeked honeyeaters P. niger, yellow-faced honeyeaters Meliphaga chrysops, whiteeared honeyeaters Meliphaga leucotis, Little Wattlebirds Anthochaera chrysoptera. Species showed seasonal variations in use, but these were not consistent across species. Between eight and 14 feeders were distributed across a 4 ha patch of heath, at least 30 m from the centre of any known honeyeater territory. Feeders consisted of commercial hummingbird feeders modified so that they had a wider drinking hole, or larger plastic bottles with a curved drinking tube. Feeders were filled with 25% by weight sugar solution for four 48 hour periods each month. Feeders were also visited (briefly) by Silvereyes Zosterops lateralis, an eastern whipbird Psophodes olivaceus and non-birds (Antechinus – a small marsupial and honeybees Apis mellifera).

 

2 

A randomised and replicated ex situ choice experiment in South Africa (Downs & Perrin 1996) found that three species of nectarivorous African songbirds (Gurney’s sugarbird Promerops gurneyi, malachite sunbirds Nectarinia famosa and amethyst sunbird N. amethystina ) all preferentially consumed sucrose over glucose or fructose when all were offered at low concentrations (0.25 moles/litre), but there were no such preferences when birds were offered higher concentrations (of 0.73 moles/litre). No species preferentially consumed higher concentrations of sucrose when give the choice of high (0.73 moles/litre), medium (0.5 moles/litre) or low (0.25 moles/litre) sucrose solutions. All solutions were provided in 125 ml feeders. A total of five malachite and seven amethyst sunbirds and five sugarbirds were tested.

 

3 

A randomised, replicated ex situ choice experiment in South Africa in 1996 (Franke et al. 1998) found that 24 pale (Cape) white-eyes Zosterops pallidus tested over 12 days preferentially fed on 20% sucrose solution (measured by weight), compared to 20% glucose or fructose solutions. There were no differences between single sugars and a mix of glucose and fructose. Twenty one birds also rejected solutions containing the other sugars if they were mixed with xylose (a sugar isolated from some nectars), with the amount of solution consumed decreasing as xylose concentration increased. Birds appeared to be able to absorb sucrose, glucose and fructose very efficiently (absorbing 97.6-99.9%) but were less able to absorb xylose (averaging 61% absorption). Solutions were provided in 25 ml pipettes with a 5 mm hole in the top.

 

4 

A randomised and replicated series of ex situ choice experiments in the Western Cape, South Africa, in 1995 (Jackson et al. 1998) found that 13 southern (lesser) double-collared sunbirds Nectarinia chalybea showed a preference for 20% by weight sucrose solution, compared to 20% fructose or ‘hexose’ (equal parts fructose and glucose) solutions, both of which were preferred to 20% glucose. In contrast, 13 female Cape sugarbirds Promerops cafer did not show a preference for different sugar types. Individuals of both species appeared to avoid solutions with xylose in them, reducing their consumption as the proportion of xylose in the solution increased. Solutions were provided in 25 ml pipettes with a glass bulb on the end with a drinking hole in it, surrounded by red nail varnish to increase visibility.

 

5 

A controlled before-and-after study on Mokoia Island, Lake Rotoruais, North Island, New Zealand (Armstrong & Perrot 2000), found that stitchbirds (hihi) Notiomystis cincta used feeders providing 20% by weight sugar solution frequently and when feeders were present they spent more time foraging for insects and less time foraging for fruit and nectar. However, there were no differences in weight gain or loss or survival rates when feeders were present, compared to when they were not. Feeders were present for 16 days at a time and then removed for 12 days. This alternation continued between January and November 1995. Annual survival in the population was low (38%) and the population appeared likely to decline despite feeding.

 

6 

A randomised and replicated series of ex situ choice experiments in 2006-7 in KwaZulu-Natal, South Africa (Brown et al. 2010), found that eight malachite sunbirds Nectarinia famosa changed preferences for different sugars changed dependent on the concentration being used. At 5% concentration the birds preferentially fed on hexose (equal parts glucose and fructose); at 10%, 15% and 20% they showed no preference and at 25% concentration they preferentially fed on sucrose. Birds also showed a preference for sucrose solutions of higher concentrations, compared to lower-concentration sucrose, although the difference between 25% sucrose and 20% sucrose was not significant. The authors note that 5% sugar solution was not sufficient to maintain the birds’ energy levels. Sugar solutions were provided in 20 ml burette tubes, moved periodically to avoid biases.

 

Referenced papers

Please cite as:

Williams, D.R., Child, M.F., Dicks, L.V., Ockendon, N., Pople, R.G., Showler, D.A., Walsh, J.C., zu Ermgassen, E.K.H.J. & Sutherland, W.J. (2018) Bird Conservation. Pages 95-244 in: W.J. Sutherland, L.V. Dicks, N. Ockendon, S.O. Petrovan & R.K. Smith (eds) What Works in Conservation 2018. Open Book Publishers, Cambridge, UK.