The latest Paper of the Month for Bird Conservation International is Differences in breeding phenology between two geographically separated populations of the ʻuaʻu (Hawaiian Petrel Pterodroma sandwichensis) and is freely available for one month.

The ʻuaʻu, or Hawaiian Petrel (Pterodroma sandwichensis), is one of two endemic seabirds found in the Hawaiian Islands.  Unfortunately it is also endangered due to a whole range of threats including introduced predators (such as cats, rats and pigs), collisions with power lines and potential threats at sea.  The majority of their colonies are located on the islands of Kauaʻi, Maui and Lānaʻi, and interestingly these different island populations are now showing genetic, morphological and behavioural differences.  Assessing potential differences in their breeding phenology is therefore an important step in helping to direct conservation measures at an island level.

Over a 12-year period we studied two island populations – those on Kauaʻi and Lānaʻi.  Cameras were deployed on hundreds of burrows, which were also checked on a near monthly basis.  We then assessed breeding pair activity from first arrival through to fledging to chart the breeding phenology of these two distinct populations.  Based on this data we found that ‘ua’u on Kauaʻi arrive in mid-April, then take a month-long exodus before returning to lay their egg in early June.  The 56-day incubation period continues until August, followed by chick rearing of 95 days.  Fledging starts around mid-October, peaks in November, and wraps up by the third week of December.  Interestingly, there were clear differences with birds on Lānaʻi where the whole process starts two weeks earlier, and fledging ends a week sooner than on Kauaʻi.

We considered this data in the context of existing data for all ‘ua’u populations across the Hawaiian Islands and found that ʻuaʻu arrive in the following order: first on East Maui, then Lānaʻi, Hawaiʻi Island, and finally Kauaʻi. These differences in timing probably contribute to the genetic differences occurring between island groups.  Why does all this matter?  Knowing exactly when ʻuaʻu breed on each island helps conservationists and land managers assess when the birds are most vulnerable—especially to introduced predators. It’s also essential for efforts like directing rescue campaigns for fallout chicks (when newly fledged chicks are grounded by artificial lights), preventing collisions with powerlines, and improving ongoing restoration and monitoring programs.  As our study has shown, at an island level this is clearly not a case of one size fits all!    And there’s more on the horizon: future studies using sound recordings and data from social attraction sites could help us understand what’s going on with non-breeding birds at the colonies.

The paper “Differences in breeding phenology between two geographically separated populations of the ʻuaʻu (Hawaiian Petrel Pterodroma sandwichensis)“, by A. F. Raine, S. Driskill, R. Sprague, J. Rothe, G. Caceres, J. Schuetz, M. McFarlin and M. S. Travers, published in Bird Conservation International, is freely available for one month.