A fundamental study revisited: Quantitative evidence for territory quality in oystercatchers (Haematopus ostralegus) usingGPSdata loggers

Abstract

A fundamental study by Ens et al. (1992, Journal of Animal Ecology, 61, 703) developed the concept of two different nest‐territory qualities in Eurasian oystercatchers (Haematopus ostralegus, L.), resulting in different reproductive successes. “Resident” oystercatchers use breeding territories close to the high‐tide line and occupy adjacent foraging territories on mudflats. “Leapfrog” oystercatchers breed further away from their foraging territories. In accordance with this concept, we hypothesized that both foraging trip duration and trip distance from the high‐tide line to the foraging territory would be linearly related to distance between the nest site and the high tide line. We also expected tidal stage and time of day to affect this relationship. The former study used visual observations of marked oystercatchers, which could not be permanently tracked. This concept model can now be tested using miniaturized GPS devices able to record data at high temporal and spatial resolutions. Twenty‐nine oystercatchers from two study sites were equipped with GPS devices during the incubation periods (however, not during chick rearing) over 3 years, providing data for 548 foraging trips. Trip distances from the high‐tide line were related to distance between the nest and high‐tide line. Tidal stage and time of day were included in a mixing model. Foraging trip distance, but not duration (which was likely more impacted by intake rate), increased with increasing distance between the nest and high‐tide line. There was a site‐specific effect of tidal stage on both trip parameters. Foraging trip duration, but not distance, was significantly longer during the hours of darkness. Our findings support and additionally quantify the previously developed concept. Furthermore, rather than separating breeding territory quality into two discrete classes, this classification should be extended by the linear relationship between nest‐site and foraging location. Finally, oystercatcher′s foraging territories overlapped strongly in areas of high food abundance.

Level of local human disturbance and feeding state determines escape behaviour in Eurasian Oystercatchers

“…The shorter FIDs exhibited by feeding oystercatchers compared with roosting ones at low tide that we observed in this study agree with our prediction that roosting oystercatchers approached by a human‐simulated predator during the period of low tide would take fewer risks by escaping sooner than feeding oystercatchers that will lose feeding time if they escape (Cooper & Frederick, 2007; Ydenberg & Dill, 1986). This is because, the prey on which shorebirds, including oystercatchers, feed in the intertidal zone of coastal habitats is presumably more exposed and accessible during low tide period (Burger, 2018; Fonseca et al, 2017; Schwemmer et al, 2017). Hence, the observed responses of the oystercatchers in this study support the optimal escape theory and are like the findings of some other studies.…”

Habitat selection can reduce effects of extreme climatic events in a long‐lived shorebird

“…Territory quality varies widely, due to both flooding risk (van de Pol et al, ) and distance to intertidal feeding sites (Ens, Kersten, Brenninkmeijer, & Hulscher, ; Schwemmer, Weiel, & Garthe, ). Breeding pairs with territories adjacent to the intertidal mudflats can directly provision their offspring, while inland pairs must collect food from the intertidal mudflats and bring them back to their offspring in the nesting territory (Ens et al, ).…”

“…Breeding pairs with territories adjacent to the intertidal mudflats can directly provision their offspring, while inland pairs must collect food from the intertidal mudflats and bring them back to their offspring in the nesting territory (Ens et al, ). The cost of provisioning for inland territories increases with distance from the shoreline due to travel time associated with each foraging trip (Schwemmer et al, ), and so coastal territories can produce around three times more fledglings than inland territories (Ens et al, ; van de Pol et al, ). It is important to note that distance to the mudflats is not a direct indicator of flooding risk.…”

State‐dependent environmental sensitivity of reproductive success and survival in a shorebird

“…Predation risk is highest during the egg-laying phase, as both parents are regularly absent from the nesting site (van de . Parents that can reduce time away from the nest can thus have higher nest survival, for example through foraging efficiently or occupying territories adjacent to the intertidal feeding grounds (Ens et al 1992, Schwemmer et al 2017. Given the suite of characteristics that define individual heterogeneity in reproductive performance, and its implications for population viability, it is important to understand how successful individuals are able to cope with environmental change.…”

“…1992, Schwemmer et al . 2017). Given the suite of characteristics that define individual heterogeneity in reproductive performance, and its implications for population viability, it is important to understand how successful individuals are able to cope with environmental change.…”