Macgillivray’s seaside sparrow
Ammodramus maritimus macgillivraii 1
The seaside sparrow (Ammodramus maritimus), which ranges from New England to southern Texas, was first described by Alexander Wilson in 1811 as the sea-side finch, Fringilla maritima. Due to subtle plumage differences, its taxonomic history is complex, but currently there are eight subspecies of seaside sparrows recognized – one being extinct. These eight subspecies are divided into two distinct groups – the Atlantic Coast group and the Gulf Coast group. The Atlantic Coast group includes the northern seaside sparrow (Ammodramus maritimus maritimus), MacGillivray’s seaside sparrow (Ammodramus maritimus macgillivraii), the extinct dusky seaside sparrow (Ammodramus maritimus nigrescens), and the endangered Cape Sable seaside sparrow (Ammodramus maritimus mirabilis). The Gulf Coast group includes Scott’s seaside sparrow (Ammodramus maritimus peninsulae), the Wakulla seaside sparrow (Ammodramus maritimus juncicola), the Louisiana seaside sparrow (Ammodramus maritimus fisheri), and the Texas seaside sparrow (Ammodramus maritimus sennetti).
Described as a full species by John James Audubon in 1834, the MacGillivray’s seaside sparrow has been considered a subspecies of seaside sparrow since at least 1899. It is known from the coastal marshes of South Carolina, Georgia, and Florida.
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The seaside sparrow is a drab, olive-gray to olive-brown bird, with a relatively long bill and short, sharp tail. It has considerable variation in size and coloration throughout its range, which has led to difficulty distinguishing subspecies. The back and breast are streaked, but this streaking is not always conspicuous.
The MacGillivray’s seaside sparrow has been described as being darker on its backside than the northern seaside sparrow, with back feathers and central tail feathers often broadly streaked with black. Streaks on the chest and sides are also broader and darker.
Birds have a distinct yellow spot over the eye. There is a gray to black moustache stripe set off by a white throat and pale buffy cheek stripe. Wing-bars are absent. The edge of the wing at the wrist is yellow.
All subspecies of seaside sparrow are about 14-15 centimeters in length with males being slightly larger than females. There appears to be a slight large-to-small trend from north to south, especially in the wing and leg bone measurements. Their tails are pointed with central feathers longer than outer ones.
MacGillivray’s seaside sparrows spend their entire life in coastal salt and brackish marshes in South Carolina, Georgia, and Florida. In South Carolina, they breed in lower elevation areas of high marsh and in managed impoundments, which are often brackish and non-tidal.
Birds in Georgia and Florida breed in higher elevation areas of natural low marsh that experience two high tides and two low tides daily. MacGillivray’s seaside sparrow is generally considered a non-migratory, sedentary subspecies, but anecdotal data and historical accounts suggest individuals make local movements between breeding and wintering seasons.
The diet of seaside sparrows consists mostly of insects, other invertebrates, and seeds. The diet can vary with season and location, but major items include grasshoppers, beetles, caterpillars, spiders, small crabs, snails, amphipods, and marine worms. They also eat many seeds, especially in fall and winter, including those of cordgrass and saltbush.
Previous MacGillivray’s seaside sparrow range maps identified North Carolina as part of the subspecies’ range. However, this area has been excluded from the range based on genetic information and a lack of suitable habitat. Areas that have been excluded from the range are from Dare County, North Carolina south to the southern boundary of Horry County, South Carolina. Recent genetic analysis supports the fact that seaside sparrows in North Carolina are more closely related to northern seaside sparrows, not MacGillivray’s seaside sparrows.
MacGillivray’s seaside sparrow’s current range extends from the northern boundary of Georgetown County, South Carolina to the St. Johns River in Duval County, Florida. This equates to approximately 270 miles (435 km) of coastline in the occupied range, with 150 miles (240 km) in South Carolina, 100 miles (160 km) in Georgia, and 20 miles (32 km) in Florida. While no population range reductions have been documented in South Carolina or Georgia to date, there has been a documented contraction of the southern range limit by approximately 100 miles (160 km) in northeast Florida. MacGillivray’s seaside sparrow formerly occupied marshes further south in Florida, through New Smyrna Beach (Volusia County), but it is widely accepted that the subspecies has disappeared from these coastal marshes.
Primary limiting factors for seaside sparrow survival and reproduction are predation, flooding, and extreme weather events. For eggs and nestlings, MacGillivray’s seaside sparrows need a nest cup that often has a canopy made from surrounding marsh grasses, interwoven to provide shelter from predation. Adult MacGillivray’s seaside sparrows have behavioral adaptations to balance the trade-off in risk from predation and flooding, and therefore, will shift nests higher or lower in marshes to contend with these risks. For example, by placing a nest lower to the surface in dense vegetation, the amount of cover to hide the nest from predators will increase but it will also increase the probability of nest flooding. Additionally, MacGillivray’s seaside sparrows avoid marshes that are near uplands, which may be an additional strategy to minimize predation risk since uplands can serve as sources of predators.
Predation is a significant mortality factor for MacGillivray’s seaside sparrow nests. The primary predators are other bird species, such as the northern harrier, American crow, and various species of owls. In addition, raccoons, American mink, rice rats, fish crows, snakes, and marsh wrens can also prey on the subspecies.
In addition to predation, tidal flooding is an important cause of nest failure for MacGillivray’s seaside sparrows. While the greatest impact may be on nests, tidal flooding can affect all stages of their life history. Tidal flooding can cause increased concentrations of predators in breeding areas, thus compounding the flooding issue. Sea-level rise is predicted to change the tidal regime by increasing the frequency and severity of tidal flooding, and MacGillivray’s seaside sparrows may have lower rates of nest success under extreme sea-level rise, especially when combined with high nest predation.
Tropical storms and hurricanes are projected to increase in frequency and size, simultaneously with increases in mean sea-level – a consequence of global climate change. Sea-level rise and storm surge from extreme climatic events lead to higher tides and increased flood risk to nesting marsh birds. A storm coinciding with the breeding season could severely decrease reproductive success in a given year.
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How you can help
MacGillivray’s seaside sparrow will benefit from continued surveys, monitoring, and research. Protecting habitats where the subspecies is known to occur and limiting development of uplands in those areas will also be beneficial for the subspecies. As threats from predation, flooding, and climate change narrow the available habitat for the subspecies, safeguarding the habitats known to harbor populations of MacGillivray’s seaside sparrow are of increased importance.
Subject matter experts
- Whitney Wiest Beisler, South Carolina Ecological Services Field Office, (843)727-4707 ext. 228; email@example.com
Federal register notices
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