Long-term patterns in the proportion of first-year waders during the non-breeding season in Scotland

To maintain stability in numbers, bird populations are dependent on sufficient young recruits to offset adult mortality. The proportion of first-year birds recruiting into populations during the non-breeding season will be influenced by breeding productivity, adult survival and immigration/emigration. To monitor long-term (1976/77 to 2021/22) changes in the recruitment of first-year waders into non-breeding populations in the Moray Firth, northern Scotland, we measured the proportion of first-year waders (Eurasian Oystercatcher Haematopus ostralegus, Common Ringed Plover Charadrius hiaticula, Dunlin Calidris alpina, Red Knot C. canutus, Purple Sandpiper C. maritima, Common Redshank Tringa totanus, Bar-tailed Godwit Limosa lapponica, Eurasian Curlew Numenius arquata and Ruddy Turnstone Arenaria interpres), originating from different biogeographical regions (Arctic, sub-Arctic and temperate regions) of the Nearctic and Palearctic parts of the East Atlantic flyway. Against a background of population decline in most wader species in the Moray Firth, most species showed no trend in the proportion of first-year birds. Only Eurasian Oystercatcher and Eurasian Curlew showed a significant decline in the proportion of first-year birds, whereas the Common Ringed Plover showed an initial increase and a later decline. For species whose numbers have declined but showed no trend in recruitment (Purple Sandpiper, Common Redshank and Ruddy Turnstone), the average proportion of first-year birds may be insufficient to offset annual adult mortality, or adult survival may have declined. The lack of a decline in the proportion of first-year birds in the latter three species does not support the possibility that first-year birds are short-stopping on their autumn migration. Smaller wader species had a higher proportion of first-year birds than larger waders. Estimated proportions of over 0.67 for first-year Red Knots and Dunlins in the Moray Firth indicate that they are not representative of the flyway populations.