Comparative Breeding Behavior of Ammospiza caudacuta and A. maritima Part 1

Comparative Breeding Behavior of Ammospiza caudacuta and A. maritima.

by Glen E. Woolfenden.

INTRODUCTION

Taxonomically the Genus _Ammospiza_ has received the attention of ornithologists for more than a century. Nevertheless, the behavior of no species of the genus has been studied extensively. The papers of Montagna and Tomkins are the only works that mention behavior and natural history in any detail. There has been an increasing awareness of the importance of ethological data and of their usefulness in systematics. For these reasons, I made a comparative study of the breeding behavior of the Sharp-tailed Sparrow (_Ammospiza caudacuta_) and the Seaside Sparrow (_Ammospiza maritima_) in New Jersey in the spring and summer of 1955.

The Seaside Sparrow is restricted to the Gulf- and Atlantic-coasts of North America, breeding north to Ma.s.sachusetts. The Sharp-tailed Sparrow breeds south to North Carolina. The overlap of the breeding ranges of the two species is therefore small. Furthermore the forms breeding in the coastal states are restricted to tidal marshes, and the geographically peripheral colonies of each species are small. Irregular nesting is the case for the northernmost colonies of the Seaside Sparrow, on Cape Cod (Griscom, 1944:317), and the same is probably true for the colonies of the Sharp-tailed Sparrow on Pea Island, North Carolina, as indicated by Montagna's failure to locate any breeding birds in July, 1941 (Montagna, 1942b: 256). The center of overlap of the ranges of the two species is in New Jersey where both forms are abundant and can best be studied comparatively.

MATERIALS AND METHODS

The adult sparrows were captured and banded, and sometimes the nestlings were banded. The standard funnel trap, baited with seeds, proved useless for capturing birds of the Genus _Ammospiza_, although migrant Savannah Sparrows (_Pa.s.serculus sandwichensis_) readily entered. A j.a.panese bird net, twenty-five feet long, was used successfully. Eighty-five Sharp-tailed Sparrows and forty Seaside Sparrows were banded at two localities.

All of the adult sparrows were banded with United States Fish and Wildlife Service numbered bands and colored celluloid bands. The colored bands I used were obtained from the Hinton Supply Company of New York City, which manufactures them for cage birds. The firm makes them in seven colors, sold at reasonable prices. With seven colors, the number of combinations, using only one colored band and one aluminum band per bird, is forty-two.

In addition, I dyed many adults and all nestlings. Alcoholic solutions of Victoria Blue B S concentrate and Alizarine Red S concentrate were used. The males were dyed red, the females blue; various areas of the body were colored in order further to individualize the birds. Although the dyes disappeared in less than a month, the markings were helpful on many occasions.

When an adult bird was captured I always s.e.xed it and ordinarily weighed and measured it. The nestlings were weighed and measured daily at intervals of 24 hours. I built a corral of hardware cloth around one Sharp-tailed Sparrow nest in order to measure the young after they left the nest. The s.e.x of any adult was ascertained by examining the cloacal area, as described by Salt (1954:61-75). s.e.x as determined by this method was corroborated by internal examination of the specimens collected.

A pan balance accurate to one-tenth of a gram was used for weighing. The adults were weighed in a cloth sack, the sack being weighed each time to prevent error owing to variable moisture and other factors.

Dragging the marsh with a rope was ineffectual in finding nests.

The birds flushed long before the rope neared them. I found nests of the sparrows by using a blind. From a blind I would determine the approximate location of a nest by watching the movements of the adult birds. Then I would either make a direct search of the vegetation or move the blind closer to find the actual site.

Many hours were spent in blinds. I had two in operation throughout the breeding season, and it was from these that most of the data on behavior were acc.u.mulated. Observations were made by means of a 7 x 50 coated binocular and on occasions by means of a 19.6x spotting telescope.

DESCRIPTION OF THE AREA

The intensive work was carried out on the marshes west of the town of Lavallette in Ocean County, New Jersey. Further observations were made at other localities in the county, in particular at the Chadwick marshes (plate 6), one mile north of the Lavallette site, where many of the Ammospizas were banded. The breeding Ammospizas of the localities are the nominate races, _A. c. caudacuta_ (Gmelin) and _A. m. maritima_ (Wilson).

Characteristic of the sand beaches of the Atlantic coast of the United States are offsh.o.r.e bars which, when exposed, form long bays parallel to the coastline. These bays become surrounded by marshes that in turn are inhabited by the two species of _Ammospiza_. The birds prefer the marshes closest to the ocean (plate 6). I made trips to the marshes on the mainland side of upper Barnegat Bay and found only a few Sharp-tailed Sparrows and no Seaside Sparrows in residence.

The island of the Lavallette marshes that I worked on was approximately 1400 feet long and 600 feet wide. One-third of the east central end of the island was covered with sand fill, pumped there several years before the study was begun (plate 1, fig. b).

The island was also ditched. The four east-west ditches are s.p.a.ced 125 feet apart; the two ditches perpendicular to these are 340 feet apart and are situated in the western portion of the island. These ditches, originally dug as a means of decreasing the mosquito population, are one foot wide and almost three feet deep. The excavated earth is deposited in a row paralleling the ditch. The entire island, excluding the sand fill is not more than two feet above normal high tide. In August, 1955, abnormally high water, a result of hurricane "Connie", rose four to five feet and covered all but the tops of the bushes and a few mounds of sand. Low tides expose no mud flats for the edges of the marsh are nearly vertical banks and the water along the edges is more than one foot deep.

The average temperature for July, compiled over a 34 year period at the Asbury Park weather station is 72.6?F. The average precipitation from May through August, acquired over the same length of time, is between 3.5 and 4.5 inches per month.

In spring and summer the prevailing winds are from the south and southwest. Therefore, the south and west sh.o.r.es of the island are subject to greater inundations by water. The fact that the island is unprotected by neighboring islands from the open expanse of the bay on this side is also of importance in this respect. The north and east sh.o.r.es, on the lee side of the island, are guarded from the open bay by nearby land. The exposed southern sh.o.r.es, where there was open mud and spa.r.s.e patches of cord-gra.s.s, were the preferred feeding areas of the Seaside Sparrows. Lack of exposed and open feeding areas may account for the absence of this species in areas that otherwise seem to fulfill the requirements of the species.

Two major drift lines were present on the island: one within a few feet of the waterline consisted mostly of dead eel gra.s.s (Zostera marina), and the other, situated close to the cattail strip, contained a variety of flotsam (pl. 2, fig. a).

FLORA

The vegetation on the island consisted chiefly of smooth cord-gra.s.s (_Spartina alterniflora_), black gra.s.s (_Juncus gerardi_), cattail (_Typha_ sp.), and marsh-elder (_Iva frutescens_). Other plants identified on the area were: common reed gra.s.s (_Phragmites communis_) and slender gra.s.s wort (_Salicornia europea_). Black gra.s.s grows on the inner, dryer portions of the marsh, and cord-gra.s.s prefers the wetter portions, growing to the edge of the water. The marsh-elder bushes mostly are restricted to the mounds of earth dug from the ditches. Cattails, in general, grow in a narrow band paralleling, but back a few yards from, the sh.o.r.eline.

Areas of mixed black gra.s.s and cord-gra.s.s occurred.

REPTILES

Diamond-backed terrapins (_Malaclemys terrapin_) were the only reptiles recorded from the study island. Several were taken on land, but the majority were seen in the waters about the marsh.

On June 27 a black snake (_Coluber constrictor_) was seen in a bushy area bordering a marsh on the mainland side of Barnegat Bay.

A few Sharp-tailed Sparrows were seen in the same locality and a singing male (G. E. W. 559) with testes 14 x 8 mm. and a female (G.

E. W. 558) with a brood patch were collected.

MAMMALS

Only two species of mammals, both abundant, were present on the study island: the meadow vole (_Microtus pennsylvanicus_) and the muskrat (_Ondatra zibethicus_). The muskrats dug burrows beneath the level of the water into the banks of the island, used the ditches as routes to the interior of the marsh and built some small houses, mostly from cattail stems.

PREDATORS

Unless the above named mammals preyed on the sparrows, all of the enemies of the colony at Lavallette were avian. Both Crows (_Corvus brachyrhynchos_) and Fish Crows (_Corvus ossifragus_) visited the local marshes frequently as did a Marsh Hawk (_Circus cyaneus_). I watched the Marsh Hawk make many pa.s.ses at what I thought were sparrows, but the only animal I ever saw caught by the hawk was a _Microtus_. The sparrows were alarmed when the hawk appeared, quickly and silently disappearing into the gra.s.s.

At least two nests on the Lavallette Marsh were destroyed by predators in the course of the breeding season of 1955. One nest of the Seaside Sparrow was empty when I checked it on July 3; on July 2 it had contained four young, three days old. On July 21 I found a dead Sharp-tailed Sparrow, approximately three days old, lying on a patch of matted gra.s.s. A hole was in the flank of the bird and blood was present about the bill. This nestling was not from a nest under observation.

Pa.s.sERINE a.s.sOCIATES

On the Lavallette marshes the only pa.s.serine a.s.sociates of the two species of _Ammospiza_ were Song Sparrows (_Melospiza melodia atlantica_) and Long-billed Marsh Wrens (_Telmatodytes pal.u.s.tris pal.u.s.tris_). Two pairs of Song Sparrows and less than six pairs of marsh wrens nested on the study area. One Song Sparrow nest was found and is plotted on the map (pl. 1, fig. b); the other pair nested somewhere along the east sh.o.r.e of the island. The Song Sparrows at the east end of the island obtained most of their food from the grounds of the Lavallette Yacht Club across fifty yards of water to the east. The pair that nested in the western portion of the island fed along the sand fill or along the bases of the marsh-elder. Their nest was built in the most extensive area of these bushes; it was placed approximately one foot above the ground in a small dead bush and gained support and concealment from the surrounding black gra.s.s. Three of the four eggs hatched on June 30, and the young left the nest on July 11. Both parents fed the offspring.

The marsh wrens fed and nested in the cattails. I never saw these wrens away from the cattails.

WINTER STATUS AND SPRING MIGRATION

Ocean County is ten miles south of the area treated in Cruickshank's regional work (1942). He considers both species as rare to casual winter residents. Concerning the spring migration of the Sharp-tailed Sparrow he says (p. 456) "The first widespread wave never comes before April 25, however, and most of the birds arrive in May." He mentions that late May is the height of migration and that stragglers are pa.s.sing through up to the middle of June. The arrival of the Seaside Sparrow in spring is similar (p. 458): the first widespread movement is in early May, the peak is reached in the third week of the month, and stragglers have been recorded through the second week in June.

I was in the field in Ocean County almost daily all spring and found no Seaside Sparrows and only two Sharp-tailed Sparrows north of Barnegat Inlet, Ocean County, before May 5. I waded through the marshes at Chadwick, Lavallette, and Island Beach State Park on April 27 when high tides covered all of the dense vegetation and saw no sparrows of the Genus _Ammospiza_. If many had been present on this date I would have seen them. On May 5 both species were plentiful on the Chadwick marshes. Furthermore, the Seaside Sparrows were defending territories.

The absence of the two species the previous day indicates a large nocturnal flight.

It was during the second and third weeks in May that the sparrows of this genus were most abundant. In this period many unbanded Seaside Sparrows were in the patches of cattails that were being defended by the resident males from other territory-holders.

One _Ammospiza caudacuta subvirgata_ (G. E. W. 545) was taken in the course of the study. It was a female (ovary: 7 x 5 mm.) weighing 15.3 grams ("moderate fat"), taken on June 8, 1955, on a marsh near the mouth of the Manasquan River on the Monmouth-Ocean County line. This marsh is decidedly less brackish than the Lavallette and Chadwick marshes. The specimen was the only _Ammospiza_ seen there and was probably a migrant, despite the late date; this subspecies is known to occur late along the Atlantic Coast south of its breeding range.

Cruickshank (1942:454-455) considers the peak of spring migration for this subspecies to be reached in late May.

To find _A. c. subvirgata_ in a marsh seemingly not saline enough for the nominate race is not surprising. _A. c. subvirgata_ breeds in marshes, along the coast of New England, which are almost fresh water (Montagna, 1942b:256). _A. c. caudacuta_ is only casual away from salt water.

TERRITORY

In a general treatise on the subject of territorialism, Nice (1933:98), summarizing Howard, stated: "Territory implies in the male bird isolation, advertis.e.m.e.nt, fixation, and intolerance." I concluded from my observations that all four requirements are exhibited by male Seaside Sparrows while none of them is well developed in male Sharp-tailed Sparrows. This subject is discussed separately for the two species.