Experimental harvest of waterfowl eggs informs management by indigenous peoples.
An experiment was conducted by the Māori tribe Ngāi Tahu and researchers (Māori and non-Māori) in Aotearoa/New Zealand, to assess how customary egg harvest regimes (removal of one-third, two-thirds or all eggs from individual nests) impact hatching success of a culturally important waterfowl species, the black swan (kakī anau, Cygnus atratus). The tribe is interested in re-initiating customary harvests of swan eggs and this study aimed to update the knowledge of harvest impacts under current environmental conditions. It was shown that partial harvests caused a loss of approximately one hatchling per egg removed, because swans replaced few of those harvested eggs yet incubated most unharvested eggs until they hatched. Conversely, harvesting an entire clutch caused a loss of approximately one hatchling for every two eggs removed, because swans often subsequently re-laid new, but smaller, clutches. in conclusion, for a given number of eggs harvested during a nesting season, removing entire clutches early during nesting could induce some re-laying and prevent abandonment of unharvested eggs in black swans. Restoring foraging habitat in degraded wetlands such as the study site could provide the plant resources these birds require to re-lay additional eggs.