BREEDING BIOLOGY OF TRISTRAM STORM-PETREL ON LAYSAN ISLAND

Breeding biology of Tristram's Storm-Petrels (Oceanodroma tristrami) was studied on Laysan Island in the Northwestern Hawaiian Islands from 3 February to 14 June 1991. Adults arrived on Laysan from mid-October to November. Most egg laying occurred in December and January and hatching in February and March. The young fledged from late April to early June at 85-92 days of age. Their growth rate was best described by the logistic curve. Adults did not begin molt of remiges until after the breeding season. Eggs hatched at only nine of 27 nests (33%) found during incubation; five of these hatchlings fledged (56%). Abandonment rates were identical at nests where we handled adults and where we inspected eggs without handling adults. Because unattended eggs were destroyed quickly by Laysan Finches (Telespiza cantans), we suggest that Tristram's Storm-Petrels that co-occur with finches seldom neglect their eggs as is common among other species of storm-petrels. Modifications caused by reaching into a burrow (e.g., widening the entrance and dislodging soil from burrow walls) may be perceived by adult storm-petrels as a signal that the burrow may collapse.