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Providing evidence to improve practice

Action: Provide supplementary food for auks to increase reproductive success Bird Conservation

Key messages

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  • Two replicated and controlled studies from the UK found that Atlantic puffin Fratercula arctica chicks provided with supplementary food were significantly heavier than control chicks. One study found differences between populations, suggesting some are more food-limited than others.
  • The two UK studies found that fed chicks fledged at the same time as controls, whilst a randomised, replicated and controlled study from Canada found that tufted puffin Fratercula cirrhata chicks supplied with supplementary food fledged later than controls.
  • The Canadian study found that fed chicks had faster growth by some, but not all, metrics.


Supporting evidence from individual studies


A controlled, replicated study on St. Kilda, western Scotland, in 1975 (Harris 1978), found that Atlantic puffin Fratercula arctica chicks fledged at significantly higher weights if they were provided daily with 50 g of sprats Sprattus sprattus, compared to control chicks (average weight of 316 g for 11 fed chicks vs. 301 g for 37 controls). Five chicks removed from burrows and fed sprats ad libitum were even heavier (365.g) while three unfed chicks with a single parent were lighter (240 g). All removed chicks and fed chicks fledged, 37 of 39 controls fledged and three of six single-parent chicks fledged. There was no difference in fledging age between fed and control chicks (40 days), but single-parent chicks took longer to fledge (45 days). A parallel study on the Isle of May (eastern Scotland) found smaller differences between treatments (removed: 367 g for six chicks; fed: 344 g for ten; controls: 331 g for 70; single-parent: 303 g for four), suggesting that St. Kilda puffins are to some degree food limited.



A replicated, controlled trial on the Isle of May, eastern Scotland, in June and July 1995 (Cook & Hamer 1997), found that Atlantic puffin Fratercula arctica chicks attained greater peak and fledging weights if they were fed daily (starting at eight days old and continued until fledging) with 25 g of sardines Sardina pilchardus, compared with control (unfed) chicks (peak weight of 319 g and fledging weight of 287 g for fed chicks, n = 22 vs. 305 g and 271 g for controls, n = 22). There was no difference in growth rates between treatments until chicks were 32 days old and no differences between growth rates of wing, head or tarsi. Fed chicks reached peak weights later than controls (peak weight at 35 days for fed chicks vs. 32 days for controls) but fledged at the same age (41 days old). Fed chicks were supplied with food by their parents significantly less often than control chicks. The authors suggest that additional weight was due to significantly less feeding by parents shortly before fledging, meaning that supplementary food provided a higher proportion of food received.



A randomised, replicated and controlled experiment on Triangle Island, British Columbia, Canada, in 1999 and 2000 (Gjerdrum 2004) found that growth rates of tufted puffin Fratercula cirrhata chicks’ culmen (upper beak) and tarsi (lower leg) were significantly higher when chicks were fed daily with either 58 g of herring Clupea sp. (in 1999) or 50 g of sand lance Ammodytes sp. (in 2000), compared to control (un-fed) chicks, although analysis revealed the effect on culmen growth was only apparent late in chick development. There was no effect of feeding on the rates of either wing growth or weight gain, and, in both years, fed chicks fledged later than unfed chicks (47-48 days at fledging for 32 fed chicks vs. 43-46 days for 32 controls). Parents of fed chicks made fewer provisioning trips but did not change the number, or species, of prey delivered each time.


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. (2019) Bird Conservation. Pages 141-290 in: W.J. Sutherland, L.V. Dicks, N. Ockendon, S.O. Petrovan & R.K. Smith (eds) What Works in Conservation 2019. Open Book Publishers, Cambridge, UK.