Abstract
This study investigates the distribution, abundance, and foraging ecology of Caspian Terns, Hydroprogne caspia, during 5 months of their non-breeding season, in the Peel-Harvey Estuary, south-western Australia. Observations were carried out at 20 sites around the estuary and 6 main areas (13 sites) where terns were abundant. Terns were observed every hour over 5 h time-blocks in the morning, midday, and afternoon, and the number of birds, number of birds foraging and time spent foraging were recorded for 10 min on the hour. From the 760 h of observation, a single overnight roosting site was identified in November, where a maximum of 147 birds were counted in February, after which time the roosting site appeared to shift. The total number of terns, foragers and proportion of time foraging varied amongst the six areas and foraging activity differed amongst times of day. Two areas, both characterised by large, sandy spits adjacent to shallow water, one adjacent to a river mouth and one near an ocean channel, were particularly important for terns and their foraging. Foraging activity was higher in the morning than at other times of day. Although salinity, air temperature, water temperature and wind speed were correlated with the total terns, foragers and proportion of time foraging, the correlations accounted for <25% of the total variation explained. The results of this study provide information for evaluating the use of Caspian Terns as bio-indicators of the Peel-Harvey Estuary and highlights the importance of this system during the non-breeding period.
Highlights
Coastal environments are highly productive and dynamic, often supporting diverse assemblages of avifauna worldwide
This study investigates the abundance, distribution and foraging ecology of the Caspian Tern population on the PeelHarvey Estuary in south-western Australia during 5 months of their, 9-month non-breeding season
Roost counts and census Surveys at the night roost site showed an increase in the mean number of Caspian Terns from 84 birds on 28 November to 147 on 11 February 2019,4 months after the end of their breeding season (Fig. 2)
Summary
Coastal environments are highly productive and dynamic, often supporting diverse assemblages of avifauna worldwide. Among them are the coastal seabirds – long-lived, often high-order, predators who feed on the rich forage-fish and invertebrate communities within these environments (Gochfeld and Burger 1996; Balance et al 2008). This research examined aspects of nesting (Collis et al 2012), chick growth and development (Lyons and Roby 2011), fledging success (Collar et al 2017), as well as foraging ecology during breeding periods (Lyons et al 2005). Studies at other colonies have examined social attraction (Hartman et al 2019), population genetics (Boutilier et al 2013), nutritional stress indicators (Patterson et al 2015), and contaminants (Su et al 2017) in birds during breeding periods. In contrast with studies on breeding colonies, little or no information is available on the ecology of Caspian Terns during their non-breeding periods
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