Foraging areas of streaked shearwaters in relation to seasonal changes in the marine environment of the Northwestern Pacific: inter-colony and sex-related differences

Abstract

As the spatial distribution of marine organisms is often affected by seasonal changes, pelagic seabirds may change their foraging areas in response to seasonal changes in the marine environment. Here, we examined the foraging area of streaked shearwaters Calonectris leucomelas, breeding at Sangan (SA) and Mikura Islands (MK), Japan, from spring to summer during pre-laying and incubation periods. Those colonies are located at the north and south of the Northwestern Pacific's Kuroshio-Oyashio transition area where high seasonal temperature changes are observed, and where, consequently, birds may show comparable responses to such changes. Our results showed that streaked shearwaters from both colonies shifted their foraging areas northwards as the season progressed. The seasonal shift of foraging areas appeared to coincide with the movement pattern of pelagic fishes that migrate northward in association with the increase in water temperature. However, the pattern of seasonal movement differed between the 2 colonies; shearwaters from SA moved their foraging area along the coastal area of the Kuroshio-Oyashio transition, while those from MK moved along the Kuroshio Extension. Our results also indicated sex-related differences in this general pattern: females showed clear seasonal changes in foraging area, while males did not. During the pre-laying period males returned to the colony frequently to defend their nests or mates, and spent less time at sea. Our results suggest that streaked shearwaters changed their foraging areas in response to seasonal changes in the marine environment, although colony location and sex-related differences in reproductive roles may constrain the birds' responses to seasonal change.

Causes and consequences of individual variability and specialization in foraging and migration strategies of seabirds

“…Males (which usually perform a greater role in nest defence) often forage more locally and visit the colony more frequently, whereas females often go on a pre-laying exodus, engaging in longer foraging trips in more productive waters to meet energetic or other nutritional requirements for the clutch (Lewis et al 2002, Yamamoto et al 2011, Hedd et al 2014, Quillfeldt et al 2014, Pistorius et al 2015. Indeed, changing energetic or nutritional requirements during the breeding cycle would explain why sex differences are apparent only at certain stages in mono morphic species such as Barau's petrel Pterodroma baraui (Pinet et al 2012) or why late-incubation trips by male southern rockhopper penguins are longer, as they do all the early chickguarding (Ludynia et al 2013).…”

Inter-Colony Differences in the Incubation Pattern of Streaked Shearwaters in Relation to the Local Marine Environment

“…Therefore, we defined the start of the incubation period as the return from the pre-laying exodus for females, and as occupancy of the burrow over a period of more than three days for males. Note that Streaked Shearwaters usually do not stay in their burrows for more than two days continuously prior to the incubation period (Yamamoto et al 2011). The end of the incubation period was defined as the hatching date of each egg.…”

“…We identified the date of return to the breeding colony using light and immersion data (Yamamoto et al 2011). Because most Streaked Shearwaters land at the breeding colony after dusk, and depart the colony before dawn (Yoshida 1981), immersion data were recorded as 0 (out of water) over the substantial period of the night that birds were at the colony.…”

“…Breeding colonies of Streaked Shearwater are distributed widely from 24°N to 42°N in latitude and from 121°E to 142°E in longitude in East and Southeast Asia, and, thereby, the characteristics of local marine environment may differ depending on the location of a breeding colony (Oka 2004). Furthermore, previous studies reported that the foraging trip duration of Streaked Shearwaters differed between the sexes depending on the reproductive stage, as females take longer trips during the prelaying period (Yamamoto et al 2011) and males tend to take longer trips during chickrearing period (Ochi et al 2010). Therefore, we might expect to observe the inter-colony and sex-related differences in the share of incubation duties in Streaked Shearwaters.…”

“…However, such studies do not provide information about foraging areas used by the birds and, therefore, cannot reveal how nest attendance patterns may be correlated with the local marine environment (but see Shoji et al 2011). Recently, miniaturised global location sensor loggers have been used to track bird movement and behavior at sea during both breeding and non-breeding periods (Croxall et al 2005;Shaffer et al 2006;Yamamoto et al 2008), as well as identify the day of return to the breeding colony (Yamamoto et al 2011). Therefore, both the timing of nest attendance and foraging areas of individuals can be examined at the same time using these global location sensors.…”