Flying south: Foraging locations of the Hutton's shearwater (Puffinus huttoni) revealed by Time‐Depth Recorders and GPS tracking

Abstract

The Hutton's shearwater Puffinus huttoni is an endangered seabird endemic to Kaikōura, New Zealand, but the spatial and temporal aspects of its at‐sea foraging behavior are not well known. To identify foraging areas and estimate trip durations, we deployed Global Positioning Systems (GPS) devices and Time‐Depth Recorders (TDR) on 26 adult Hutton's shearwaters during the chick‐rearing period in 2017 and 2018. We found Hutton's shearwaters traveled much further from their breeding grounds at Kaikōura than previously considered, with most individuals foraging in coastal and oceanic areas 125–365 km south and near Banks Peninsula. Trip durations varied from 1 to 15 days (mean = 5 days), and total track lengths varied from 264 to 2,157 km (mean = 1092.9 km). Although some diving occurred in near‐shore waters near the breeding colony, most foraging was concentrated in four regions south of Kaikōura. Dive durations averaged 23.2 s (range 8.1 to 71.3 s) and dive depths averaged 7.1 m (range 1.5 to 30 m). Foraging locations had higher chlorophyll a levels and shallower water depths than nonforaging locations. Birds did not feed at night, but tended to raft in areas with deeper water than foraging locations. Mapping the spatial and temporal distribution of Hutton's shearwaters at sea will be fundamental to their conservation, as it can reveal potential areas of overlap with fisheries and other industrial users of the marine environment.

At-sea foraging behaviour in Hutton’s shearwater (Puffinus huttoni) as revealed by stable isotope analysis

“…2d), were more consistent with induced tail feathers suggesting these represent prey items of the Hutton's shearwater diet. Thus, our isotopic data from the induced tail feathers are consistent with tracking data that indicates most foraging dives occurred at coastal sites (Canterbury Bight and Pegasus Bay) and oceanic banks (Mernoo Bank and Urry Bank) near Banks Peninsula (Bennet et al 2019). Although we cannot discount the possibility that the Hutton's shearwater may sometimes forage on near-shore Kaikōura on small fish, depending on the trophic discrimination factor ratio, it is more likely they are primarily feeding on zooplankton when at the more distant Banks Peninsula.…”

“…Using isotopic analysis of induced Hutton's shearwater (Puffinus huttoni) feathers and prey collected from potential foraging locations, we show that foraging at sea occurs primarily south of their breeding colony, in the seas surrounding Banks Peninsula, an area to which they had been tracked previously using GPS locators (Bennet et al 2019). The apparent lack of foraging within the Kaikōura near-shore area was not expected as birds are regularly seen rafting and flying in this area in large numbers.…”

“…Understanding the spatial distribution of a species can enable a more accurate assessment of diet and key areas used for foraging. During the breeding season, Hutton's shearwaters have been tracked flying south from their breeding colony at distances of 125-365 km, in an area off the coast of Banks Peninsula and near the Chatham Rise (Bennet et al 2019). The δ 13 C and δ 15 N composition of zooplankton species collected between 85-220 km off the coast of Banks Peninsula (Fig.…”

“…To determine the δ 13 C and δ 15 N values of potential shearwater prey items (zooplankton and fish), samples were collected at two sites: (1) between two to eight km off the Kaikōura coast, an area near the breeding colony where shearwaters are often seen in large rafts and potentially feeding, and (2) off the coast of Banks Peninsula (Fig. 1), an area of offshore seas c. 100 km south of the breeding colony to which Hutton's shearwaters have been tracked by GPS (Bennet et al 2019). Collecting in Kaikōura was done with an oblique tow using a box-pyramid design plankton net (250 μm).…”

“…Direct collection techniques to determine diet can be invasive, and these samples may be limited in temporal and spatial scope, or difficult to identify if partially digested (West & Imber 1985;Barrett et al 2007). Although recent developments in tracking technology have greatly aided in determining movements and locations of seabirds in the marine environment (Matsumoto et al 2017;Alonso et al 2018;Bennet et al 2019), linking locations with variation in diet is still problematic as the occurrence of a bird in an area does not necessarily mean they are feeding nor can their diet be determined from location data alone.…”