Su­gar wa­ter is good for bi­rds

Dr Mark Bro­wn, Na­tu­re’s Val­ley Trust:

Knysna-Plett Herald - - Letters | Briewe -

As a pro­fes­si­o­nal or­nit­ho­lo­gist I ha­ve stu­died nec­tar-fee­ding bi­rds and the plants they pol­li­na­te for ne­ar­ly 20 y­e­ars. I ha­ve al­so con­ducted re­se­arch on the im­pact of fee­ding bi­rds in ur­ban a­re­as, and tried to ex­a­mi­ne the que­s­ti­ons com­mon­ly rai­sed, such as “do bi­rds be­co­me de­pen­dent on my fee­ding?”.Al­low me to com­ment on so­me com­mon mis­con­cep­ti­ons.

Fir­st­ly, su­gar is not bad for bi­rds at all. Nec­tar in flo­wers is al­most pu­re­ly su­gar wa­ter, with very few ex­cep­ti­ons. The­re are no vi­ta­mins, no pro­teins (very few bi­rds ac­tu­al­ly in­ge­st pol­len at all), and no ad­di­ti­o­nal nu­trients. Most flo­wer nec­tar stu­died con­sis­ts al­most en­ti­re­ly of three main su­gars, na­me­ly su­cro­se, glu­co­se and fruc­to­se. Su­cro­se is a di­sac­cha­ri­de su­gar, com­po­sed of two mo­no­sac­cha­ri­des, glu­co­se and fruc­to­se. Plant nec­tars will either ha­ve su­cro­se, or glu­co­se and fruc­to­se or a mix­tu­re of the three su­gars in them. Sun­bi­rds and su­gar bi­rds are very ef­fi­cient at su­gar di­ge­s­ti­on, ex­tracting o­ver 99% of the e­ner­gy in such nec­tars (yes it has been me­a­su­red!).

Bi­rds ha­ve a much hig­her me­ta­bo­lism than ours – their bo­dy tem­pe­ra­tu­re is an in­cre­di­ble 42ºC, and with their lar­ge sur­fa­ce a­rea to vo­lu­me ra­tio (due to their small bo­dy si­ze), they lo­se he­at to the en­vi­ron­ment much quic­ker than us. T­his, cou­pled with their fast-pa­ced flying li­fe­sty­le, me­ans they need much hig­her e­ner­gy lo­ads than us.

A sun­bi­rd fee­ding on an a­vera­ge plant nec­tar will con­su­me three ti­mes its bo­dy weig­ht in a single day to main­tain e­ner­gy ba­lan­ce. We can’t e­ven con­su­me 10% of our bo­dy weig­ht in a day, so com­pa­ri­sons are point­less. The nec­tar in plants pol­li­na­ted by sun­bi­rds and su­gar bi­rds is ty­pi­cal­ly in the ran­ge of 15 to 25% con­cen­tra­ti­on, and tho­se pol­li­na­ted by oc­ca­si­o­nal nec­tar-fee­ding bi­rds li­ke whi­te-ey­es, we­a­vers, bul­buls etc is in the ran­ge of 8 to 15%.

Sun­bi­rds need a mi­ni­mum of 10% to meet e­ner­gy re­qui­re­ments. Con­cerns that a hig­her con­cen­tra­ti­on will at­tract in­sects ha­ve me­rit, but so­lu­ti­ons 10 to 15% do not at­tract them of­ten at all – the plants they pol­li­na­te ty­pi­cal­ly ha­ve so­lu­ti­ons with con­cen­tra­ti­ons of 30 to 60%. Con­cen­tra­ti­ons a­bo­ve 10% will not up­set bi­rds’ sto­ma­chs – as is thoug­ht by so­me. As men­ti­o­ned a­bo­ve, their na­tu­ral nec­tar ran­ges from 15 to 25%, and you can e­ven sa­fely feed bi­rds so­lu­ti­ons up to 50% or mo­re wit­hout ill ef­fect.

The­re is one group of bi­rds, star­lings, that can­not di­ge­st su­cro­se, so w­hen they feed on it they get os­mo­tic di­ar­rhoea, ho­we­ver, they le­arn t­his quick­ly and will a­void fee­ders on­ce they ha­ve tried them a few ti­mes. The plants they pol­li­na­te, li­ke al­oes, red hot po­kers and co­ral trees, ha­ve on­ly glu­co­se and fruc­to­se in their nec­tars. All ot­her nu­trients are a­chie­ved by ot­her com­po­nents of a bi­rd’s diet – e­ven sun­bi­rds and su­gar bi­rds in­clu­de a high per­cen­ta­ge of in­sects in their diet for ex­am­ple. A sim­ple 10 to 20% plain ta­ble-su­gar so­lu­ti­on is, in fact, the clo­sest na­tu­ral mi­mic to na­tu­ral nec­tar that you can get.

Se­cond­ly, bi­rds do not be­co­me de­pen­dent on bi­rd fee­ders. Flo­wers pro­du­ce nec­tar con­stant­ly, and the­re are new flo­wers in an a­rea all the ti­me. In a trans­for­med ur­ban en­vi­ron­ment, the­re is no re­a­son why not to con­stant­ly feed bi­rds. The­re are litt­le to no stu­dies that show dis­rup­ti­on to pol­li­na­ti­on sy­s­tems in ur­ban a­re­as, sim­ply be­cau­se our nec­tar fee­ders form one small part of an in­di­vi­du­al bi­rd’s fora­ging ran­ge. My own work, pul­sing be­t­ween fee­ding and not fee­ding, with rin­ged bi­rds (in­di­vi­du­al­ly mar­ked for i­den­ti­fi­ca­ti­on), shows that bi­rds do not be­co­me de­pen­dent on single fee­ders at all, but rat­her vi­sit them as one stop al­ong their daily fee­ding trips.

* For mo­re in­for­ma­ti­on on re­spon­si­ble fee­ding tips for bi­rds in ur­ban a­re­as, p­le­a­se vi­sit the Gar­den Rou­te Bi­rds Fa­ce­book pa­ge – the­re are re­gu­lar ar­ti­cles and tips pos­ted the­re, and it is a won­der­ful plat­form to share your bi­rds with ot­hers.

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