Despite major losses in nesting habitat throughout Hawaiʻi, Wedge-tailed Shearwaters (ʻUaʻu kani) are increasing following conservation efforts to control introduced predators and to restore native vegetation at breeding sites. At the Freeman Seabird Preserve, the collaborative research program that began in 2009 has documented that this unique urban colony has quadrupled in size, from less than 200 breeding birds to over 800 breeding birds (Hyrenbach & Hester 2022).
Caption: Yearly colony census during the peak chick incubation period show a long-term increase in the number of nests at the Freeman Seabird Preserve. On average, the colony grows by 24.9 nests (+/- 5.3 S.D.) each year.
Since 2009, researchers studying the shearwaters at the Freeman Seabird Preserve have learned about their lives at the colony and in the ocean. Explore what we have learned in the tabs below.
Seabirds must return to land to raise their chicks and ʻUaʻu kani parents at FSP look for safe places in rock crevices and artificial clay shelters to raise their single chick. Some of the questions we ask involve: “how many birds return to breed”, “how long are the eggs incubated by the parents”, “do the dates when chicks hatch vary from year to year”, “how well are chicks growing each year”, and “do the artificial nests provide safe nest sites”?
Starting in early June, the shearwater lay and incubate a single egg, which start hatching in late July. By the end of August, all the chicks have hatched. The parents feed their chicks until they fledge, starting in the middle of November.
Caption: Distribution of incubation durations for 37 nests monitored daily revealed a mean incubation of 51.1 ± 1.4 S.D. days (median = 51, range = 47 – 54).
The hatching date influences the growth patterns of the chicks, with the chicks that hatch earlier in the year attaining a larger body mass. Chicks reach their maximum (peak) body mass in late October, when they are 80 – 90 days old. The mass of the chicks starts declining in early November, their parents stop delivering food to the nest. This period of fasting and weight loss stimulates the chicks to leave the nest.
Nevertheless, these dates also vary from year to year, depending on the food conditions at sea. In a “cold-water” year (like 2010), chicks attain a larger peak mass (median weight = 495 grams) sometime in late October (median age = 81.5 days). In a “warm-water” year (like 2009), chicks attain a lower peak mass (median weight = 452.5 grams) about one week later (median age = 86.5 days).
Learn about the shearwater breeding cycle, and ocean conditions influence their breeding success: