Provide supplementary food for gannets and boobies to increase reproductive success

Overall effectiveness category Unknown effectiveness (limited evidence)
Number of studies: 2
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How is the evidence assessed?

Effectiveness

33%
Certainty

25%
Harms

0%

Calculating overall effectiveness category

Study locations

Key messages

A small controlled study in Australia found that Australasian gannet Morus serrator chicks were significantly heavier if they were supplied with supplementary food, but only in one of two years. Fledging success of fed nests was also higher, but not significantly so.
A randomised replicated and controlled study in the Galapagos Islands found that fed female Nazca boobies Sula granti were more likely to produce two-egg clutches if they were fed, and that second eggs were significantly heavier.

About key messages

Key messages provide a descriptive index to studies we have found that test this intervention.

Studies are not directly comparable or of equal value. When making decisions based on this evidence, you should consider factors such as study size, study design, reported metrics and relevance of the study to your situation, rather than simply counting the number of studies that support a particular interpretation.

Supporting evidence from individual studies

A small controlled study at a marine reserve in Queensland, Australia, in the breeding seasons of 1997-8 and 1998-9 (Bunce 2001) found that Australasian gannet Morus serrator chicks were reached significantly heavier weights in 1997-8 when they were fed every 2-3 days (starting at five days old and continuing until 40 days old) with approximately 5% of their bodyweight in pilchards Sardinops sagax, compared to control (unfed) chicks, however there were differences in weight in 1998-9 were not significant, although trends were in the same direction (1997-8: maximum weight of approximately 3900 g for fed chicks, n = 4 vs. approximately 3250 g for controls, n = 8). Over both years fledging success was higher for fed nests, but this was not significant (100% fledging success for fed nests vs. 90% for controls). This study also investigated the impact of adding foster chicks to gannet nests (see ‘Foster eggs or chicks with wild conspecifics’).
Study and other actions tested
Referenced paper
Bunce A. (2001) Effects of supplementary feeding and artificial twinning on nestling growth and survival in Australasian gannets (Morus serrator). Emu, 101, 157-162.
A randomised, replicated and controlled trial on Isla Española, Galapagos Islands, Ecuador, in the 1997-8 breeding season (Clifford & Anderson 2001) found that female Nazca boobies Sula granti were more likely to produce two-egg clutches if they were fed at least 200 g of mullet Mugil cephalus twice daily, compared with control (unfed) females (92% of 49 fed females produced two eggs vs. 70% of 50 control females). Second eggs were also slightly larger from fed females, compared to controls (68 mm³ for 44 eggs from fed females vs. 66 mm³ for 32 from control females), first-laid eggs were no different between groups. Egg laying date and laying interval were similar between treatments. Females were fed until ten days had passed without laying an egg.
Study and other actions tested
Referenced paper
Clifford L.D. & Anderson D.J. (2001) Food limitation explains most clutch size variation in the Nazca booby. Journal of Animal Ecology, 70, 539-545.

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. (2020) Bird Conservation. Pages 137-281 in: W.J. Sutherland, L.V. Dicks, S.O. Petrovan & R.K. Smith (eds) What Works in Conservation 2020. Open Book Publishers, Cambridge, UK.

Where has this evidence come from?

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This Action forms part of the Action Synopsis:

Bird Conservation

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