2018 Summary: A Field Study of Saltmarsh Sparrows (Ammodramus caudacutus) in Narragansett Bay, Rhode Island.
Steven E. Reinert, Deirdre E. Robinson, Katie Christ, Jim O’Neil
Illustrations: Evan Lipton
September 30, 2018
INTRODUCTION.On June 16, 2016, DER photographed a color-banded Saltmarsh Sparrow during bird survey work at Jacob’s Point salt marsh in Warren, RI. Subsequent capture of the banded bird revealed a female sparrow that had been color-banded in Pinellas County, Florida, onOctober 31, 20151. This discovery prompted further exploratory work at Jacob’s Point which supported its selection as our study site. InMay of 2017 we initiated a comprehensive, multi-year field study of Saltmarsh Sparrow breeding ecology and survivorship at this 19-ha salt marsh (Figs. 1 and 2). Principal objectives of this research are to (1) determine habitat characteristics associated with nest-site selection, (2) monitor the reproductive success of the population including the impact of monthly flooding tides on nest success, (3) via mark-recapture efforts determine rates of inter-annual mortality, and (4) apply our findings to predict impacts of various magnitudes of sea level rise (to as fine a degree as 2 cm) on the near- and long-term survival of Saltmarsh Sparrows in Narragansett Bay, RI. This report presents the results of our fieldwork through the first two breeding seasons (2017 and 2018).
STUDY AREA. Jacob’s Point is a 14-ha salt marsh bordering the east shore of the Warren River on upper Narragansett Bay (Figs 1 and 2). The marsh is owned by the Warren Land Conservation Trust which has graciously granted our research team access to the site for the five year study period. A narrow sand/upland-barrier ridge separates the marsh from the bay. Tidal waters enter the estuary via two tidal channels that breach the ridge and flow east and south, respectively, into the marsh interior. The extreme southern segment of the marsh is separated from the larger wetland by an elevated road-bed constructed in the 1930s. Tidal flow is maintained to this southern tract via two, 1.5-m culverts running north-south beneath the road-bed along the courses of the original marsh channels.
Vegetation.The Jacob’s Point marsh is dominated by “salt meadow” communities of the high marsh. The salt meadow grassland is comprised of stands or mixed communities of Spartina patens (salt marsh hay), Distichlis spicata (spike grass), and Juncus gerardi (black grass). In the eastern one-half of the marsh, and south of the road-bed, the salt meadow community intergrades with the shrubby plant, high tide bush (Iva frutescens) in areas of relatively high marsh-surface elevation. Ivaoccurs in dense clumps with sparse grassy growth beneath, or in salt-meadow dominated patches with scattered Ivaplants or clumps. Ivais also present as a band of dense, shrubby habitat along marsh-upland edges. Salt marsh cordgrass (Spartina alterniflora) occurs in two forms at Jacob’s Point: (1) a tall form (>1 m) grows within the regularly-flooded intertidal zone along the upper elevations of creek- and ditch banks (“low marsh”); and (2) a shorter form (<1 m), “high-marsh cordgrass”, which grows in small patches on the high marsh where it intergrades with the salt meadow grasses.
METHODS.
Trapping and marking. During 2017, we set mist-nets during 19 days between 23 May and 7 August; in 2018, we set nets during __ days between __ May and __ August. In both years, nets were set in arrays to capture roaming adults, primarily (1) perpendicular to tidal channels where they foraged, and (2) near nests to capture attending females. We used one 12-m net, and from one to six, 6-m nets. All adult Saltmarsh Sparrows received a USGS-issued aluminum band plus a unique combination of three colored bands (one on the leg with the aluminum band, and two on the opposite leg). Nestlings were banded with aluminum bands only during 2017. In 2018, we banded nestlings with a combination of an aluminum band on one leg, and one colored band on the other leg such that there was a unique two-band combination per brood (nest).
Nest measurements. When a nest was deemed inactive we collected a set of data including a standard set of photographs of the nest and nest-site, the height in millimeters of the nest from substrate-to-rim, the plant species supporting and immediately surrounding the nest—ranked by dominance per species—and the distance to the nearest Iva frutescensplant. We preserved the elevation of each nest by driving a 40-50-cm stake (the “elevation stake”) into the peat such that the top of the stake was flush with the nest-rim.
Tidal elevation. Prior to the 2018 breeding season we placed a tide gauge in a low-lying area of the high marsh. The gauge consists of a 1.5” x 96” (__ cm x __ cm) slotted angle-rod driven ~ 1.5 m into the mineral soil underlying the marsh peat. Nested in the angle, and extending from the marsh surface ~ 1.5 m to the gauge top is a 2.5-cm wide oak stake. A metric tape is attached to the stake along one exposed surface; the adjacent surface is chalked such that a flooding tide leaves a water-mark at the level of peak amplitude. The gauge is read by measuring from the top of the steel bar down to the chalk mark (see Figure 3).
Nest elevations. On September 29, 2018, we used a CST/berger Horizontal/Vertical Rotary Laser Level and rod to measure elevations of nests relative to local bench marks. The graduated rod was read while placed (1) on top of each nest elevation stake, (2) on the marsh substrate beneath each nest, and (3) on top of the tide gauge (steel bar).
RESULTS.
Mark and recapture.
During the 2016, 2017, and 2018 breeding seasons, we captured and banded 88 adult Saltmarsh Sparrows, 63 nestlings, and one fledgling (Table 1). Of the 88 adults captured, 38% (41% of 51 adults captured in 2017, and 31% of 32 adults captured in 2018) were females (Table 2). None of the nestlings or fledglings captured in 2016 or 2017 were recaptured in subsequent years.
Table 1. Captures by age class and year.
|
Band year |
2016 No. (%) |
2017 No. (%) |
2018 No. (%) |
Total No. (%) |
| Adult |
5 (71) |
51 (54) |
32 (63) |
88 (58) |
| Fledgling |
0 (0) |
1 (1) |
0 (0) |
1 (1) |
| Nestling |
2 (29) |
42 (45) |
19 (37) |
63 (41) |
| Total |
7 (100) |
94 (100) |
51 (100) |
152 (100) |
Table 2. Captures of adult sparrows by sex and year.
|
Band year |
2016 No. (%) |
2017 No. (%) |
2018 No. (%) |
Total No. (%) |
| Female |
2 (40) |
21 (41) |
10 (31) |
33 (38) |
| Male |
3 (60) |
30 (59) |
22 (69) |
55 (62) |
| Total |
5 (100) |
51 (100) |
32 (100) |
88 (100) |
During 2018, we recaptured 12 (54%) of 21 adult-female, and 13 (43%) of 30 adult-male sparrows captured in 2017. Two of the males recaptured in 2018 were also recaptured in 2017 after having been captured as adults during June of 2016.
Nest-site vegetation.
Nests were place in three generalized site-types: (1) salt meadow… (2) salt meadow/cordgrass… (3) Iva…
Nest Success.
During 2017 we found 24 nests, 21 of which had live contents (eggs or nestlings) when found; during 2018 we found 32 nests, 27 of which had live contents. Nests found empty are not included in our summaries and analyses of nest success. A total of 172 eggs and 101 nestlings were documented in the 48 active (2017/2018) nests. Of the 101 nestlings, 61 were banded, 30 of which were among 34 total fledglings (Table 3). Observations made in both years confirmed that small numbers of young had fledged from nests we had not found.
Table 3. Nestling statistics
|
Band year |
2017 n |
2018 n |
Total n |
| Total eggs |
75 |
97 |
172 |
| Total nestlings |
48 |
53 |
101 |
| Nestlings banded |
42 |
19 |
61 |
| Nestlings fledged |
13 |
21 |
34 |
| Banded nestlings fledged |
13 |
17 |
30 |
Six (29%) of 21 nests monitored during 2017 were successful (fledged one or more young) vs. 9 of 27 (33%) during 2018. In 2017, eleven (53%) of the 21 nests monitored lost contents to predation, vs. five (18%) of 27 nests in 2018; in 2017, 38% (8 of 21) had one or more nestlings destroyed by flooding tides vs. 2018 when over one-half (14 of 27) of nests exhibited such losses. Data on nest and tidal elevations reveals that in both years many of the nests that were depredated would likely have been lost to flooding had they survived to the time of encroachment of flooding new-moon high tides.
[Enter here relationship of nest success with vegetation, elevation, and time-of-season.]
Table 4. Fates of nests by year.
|
Nest fate |
2017 No. (%) |
2018 No. (%) |
Total No. (%) |
| All nestlings fledge |
2 (10) |
5 (19) |
7 (15) |
| Partial success: tidal flood |
3 (14) |
2 (7) |
5 (10) |
| Partial success: predation |
1 (5) |
2 (7) |
3 (6) |
| All nestlings depredated |
10 (48) |
3 (11) |
13 (27) |
| All nestlings drown: tidal flood |
5 (24) |
12 (44) |
17 (35) |
| All nestlings drown: storm flood |
0 (0) |
1 (4) |
1 (2) |
| Nest abandoned |
0 (0) |
2 (7) |
2 (4) |
| Total |
21 (100) |
27 (100) |
48 (100) |
Spatial Distribution of nests.
Nests of female Saltmarsh Sparrows were clustered in four discrete activity centers, three of which were used in both 2017 and 2018 (Fig. 4). In future analyses we will attempt to identify characteristics of these patches that make them attractive to nesting sparrows, to include: substrate elevation, vegetative composition at the nest site, and proximity of nest to Ivaplants.
Discovery of male sparrows through the breeding season.
Other results.
During the 2017 breeding season, video of females attending nestlings was captured by KC at two nests, approximately 20 min per nest. A color-banded male visited one of the nests; we speculated that this male was seeking to find and copulate with the attending female. Observations after the 2017 nesting season revealed that two males color banded at Jacob’s Point on 27 May and 10 July, respectively, remained on the marsh till at least 27 September when they were photographed foraging along creek banks on seed-bearing stems of low-marsh Salt marsh cordgrass (Spartina alterniflora).
FUTURE WORK.Our research goals for the 2019 breeding season are to (1) repeat our mark-recapture and nest-monitoring field efforts of the 2017 breeding season; (2) calculate return-rates of adult and juvenile Saltmarsh Sparrows; and (3) quantify nest and tidal-height elevations to enable assessments of the impacts of sea-level rise on nest success.
Figure 3. Gauge used for measuring peak-tide elevations at Jacob’s Point salt marsh. Pictured is a reading of 80.9 cm from the zero point at top of steel rod.
Figure 4. Clustering of Saltmarsh Sparrow nests at Jacob’s Point Salt Marsh. Purple ovals delineate nest clusters from 2017; orange ovals from 2018. The overlapping areas illustrate the high degree of preference for certain marsh tracts for nest placement both within and between years.