Discussion
The study provided new insights into the origins of dunlins migrating
along the EAAF and a different perspective on the subspecies composing
Dunlin populations on the flyway. In previous studies, how many Dunlin
subspecies migrate along the EAAF was not rigorously determined. The
combined results of ring recoveries and flag resightings from this study
and previous research (Lagassé et al., 2020; Lagassé et al., 2022)
indicated that the subspecies C . a. sakhalina , C. a.
actites , C. a. kistchinski , and C. a. arcticola staged at
Jiangsu in autumn. The result of recoveries and resightings suggested
that compared with other subspecies, more individuals from C. a.
kistchinski and C. a. actites were staging in southern Jiangsu
Province, which is an important site to replenish energy reserves for
those individuals from the Kamchatka Peninsula and Sakhalin Island. In
addition, recoveries and resightings also provided general indications
of the routes of dunlin subspecies along the EAAF (Supporting
information Fig. S1).
Identification of C. a. arcticola and C. a. actiteswas important, because a recent study showed that survival is relatively
low for the arcticola subspecies and that the population size ofC. a. actites is relatively small (Weiser et al. 2018). The
population of subspecies C. a. actites is thought to
number less than 1000 individuals, compared with over 500,000 for the
other subspecies (Johnston et al. 2015). Thus, the study indicated that
the coastal intertidal flats in the study area are important to the
conservation of priority dunlin subspecies.
The application of multiple approaches can improve the effectiveness of
population identification and studies of migration in most cases.
Because most birds and subspecies of birds have highly similar
morphology, it is difficult to accurately determine differences among
species or subspecies by one specific method. Resighting and recovery
data are one of the many types of data obtained from long-term fieldwork
and represent a large investment. Although molecular methods cannot
designate all individuals to one lineage or one subspecies, phylogenetic
analysis can substantially increase understanding of dunlin population
structure and help to realize approximate migratory phenology. Genetic
data and phenotypic characters are both widely used in studies of
shorebird phylogeny and taxonomy (Popovic et al. 2019). Phenotypic
characters may be useful in probing the composition of populations
(Rheindt et al. 2011). Hence, this study combined data of resighting or
recovery and morphological and molecular analyses to comprehensively
delineate dunlin population structure and migratory connectivity.
The analysis of mtDNA sequence data provided detailed information on the
population composition and migratory connectivity of dunlin subspecies
at Jiangsu. The haplotypes from Jiangsu had sister relationships with
different dunlin subspecies and shared some haplotypes with those
subspecies. Haplotypes from Jiangsu suggested the occurrence of six
subspecies grouped into two lineages: Alaskan and Beringian. This result
indicated that the dunlin population in Jiangsu was composed of
different subspecies and that the nonbreeding ranges of those subspecies
overlapped substantially in Jiangsu. Similar observations are reported
in Portugal (Lopes et al. 2006).
The morphological difference between Alaskan and Beringian lineages is
consistent with that among subspecies from the Far East and Alaska.
Therefore, individuals in the Alaskan lineage included C.a. arcticola and C. a. pacifica and individuals in
the Beringian lineage included C . a. actites , C .a. kistchinski , and C . a. sakhalina. Similar to the
descriptions of dunlin subspecies (Greenwood 1984, 1986), males of
subspecies from Alaska had shorter bills and longer wings than those
from the Far East, whereas females of subspecies from Alaska had longer
bills and wings than those from the Far East.
Although the six subspecies could not be accurately separated, it is
plausible that at least four dunlin subspecies previously thought to
share winter ranges along the central coast of eastern Asia far-stage in
China (C . a. actites , C . a. kistchinski ,C . a. sakhalina , and C. a. arcticola )
(Bentzen et al. 2016, Choi et al. 2010, Miller et al. 2014, Tomkovich
1986). The subspecies C. a. hudsonia and C. a.
pacifica from breeding grounds in North America were unexpected,
because they were not thought to stage on the coast of eastern China
(Miller et al. 2014). However, in this study, the two subspecies most
likely occurred in Jiangsu.
Because of changes in populations, different populations of dunlin might
be represented to a different extent in the 2 years. However, distinct
clades were not detected between the 2 years, and only 10 haplotypes
were shared between the sample periods (Supporting information Fig. S2).
This may be due to the indistinct phylogenetic relationships among the
six subspecies (Miller et al. 2014). By combining size measurements and
molecular genetic analyses, the results of this study highlight the need
to reassess the composition and migratory routes of subspecies at the
level of subspecies. Morphology can help with an intuitive feeling for
the subspecies of dunlin. The morphological data from 2015 and 2016
indicated that bill and wing lengths differed between the 2 years, but
those differences were in opposite directions for the two sexes. Dunlin
were captured considerably later in autumn 2016 (26 September to 6
October) than in autumn 2015 (12–20
September), so apparent annual differences might be spurious and only
represent differences in migration timing among subspecies.
Previous studies demonstrate consistent migration timing among breeding
populations, which correlates with geographical locations of breeding
grounds (Grattarola et al. 1999, Jahn et al. 2013). In addition,
significant differences in morphological characters were observed
between Alaskan and Beringian lineages, which can help determine
breeding origin. Moreover, compared with the number of Beringian and
Canadian individuals, the number of Alaskan individuals was greater in
2016 compared to 2015. This difference might be a possible reason for
the difference in characters between the two years. However, the
differences between the two lineages could not entirely explain the
differences in individuals between the sample periods. This result might
be explained by variable proportions of different lineages or a
difference in the timing of migration of subspecies.
The above findings provided additional evidence on the importance of the
Jiangsu mudflats in providing migratory connectivity for subspecies and
strengthened the case that protective measures are needed. There is some
evidence that populations of some priority dunlin subspecies that stage
at Jiangsu, such as C. a. arcticola , C. a. actites , andC. a. sakhalina , are declining (Johnston et al. 2015, Weiser et
al. 2018). The conservation of stopover sites to maintain the
connectivity of migration is important for long-term population
persistence of subspecies from the Beringian realm (Soikkeli 1967).
Conversion of intertidal shorebird habitats to land for industry and
farming, construction of China’s new great wall along the seacoast, and
invasion of mudflats by exotic cordgrass (Spartina sp.) all
contribute to rapid losses in the extent of intertidal shorebird
habitats (Li et al. 2022, Ma et al. 2014). Although measures to protect
the Jiangsu mudflats and their enormous contribution to the future of
shorebird populations should be implemented, additional conservation
action is still required. This study draws attention to the huge
geographical area from which migrating dunlin subspecies using the
Jiangsu coast are drawn. Further research of this type is needed that
focuses on numbers of individuals and population trends of different
dunlin subspecies staging in Jiangsu and the timing of their migrations.
The approach used in this study should also be extended to other
shorebird species using this important stopover site.
Funding This work was supported by the Basic Scientific
Research Program of National Nonprofit Research Institutes (Nos.
ZX2022QT025 and GYZX210405), migratory shorebirds study program from the
Jiangsu Forestry Bureau, and the Jiangsu Academy of Forestry Youth
Foundation (JAF-2022-01).
Conflicts of interest No conflicts of interest or competing
interests.
Permits Dunlin capture,
tagging, and sampling were conducted under a special methods permit from
the Jiangsu Forestry Bureau and National Bird Ring Center.