Comparative Breeding Behavior of Ammospiza caudacuta and A. maritima Part 3

TABLE 1--DAILY WEIGHT IN GRAMS OF NESTLING SEASIDE SPARROWS AND SHARP-TAILED SPARROWS FROM LAVALLETTE, OCEAN CO., NEW JERSEY.

======+================================================================+ Day _Ammospiza maritima_ Average ------+---------+------+---------+------+------+------+------+---------+ 0 ... 2.2 2.3 ... ... 2.2 1.8 2.1 1 3.0 3.3 3.5 3.7 3.3 2.6 2.1 3.1 2 4.6 5.0 5.2 5.0 4.8 3.7 3.0 4.5 3 7.0 5.5 7.2 6.9 6.9 5.9 4.7 6.3 4 9.4 8.1 10.6 9.1 9.1 7.6 6.4 8.6 5 12.5 11.1 12.3 11.4 11.1 9.9 8.7 11.0 6 14.6 13.1 [1]11.1 13.9 13.7 12.6 9.6 13.0 7 [1]11.6 13.9 12.1 15.1 14.8 14.3 11.8 13.7 8 14.9 15.5 13.4 14.9 14.8 14.6 12.4 14.4 9 15.2 15.8 13.8 16.2 16.1 16.0 14.4 15.4 10 ... ... ... ... 15.9 15.5 14.3 15.2 ------+---------+------+---------+------+------+------+------+---------+

------+---------+------+---------+------+------+---------+ Day _Ammospiza caudacuta_ Average ------+---------+------+---------+------+------+---------+ 0 1.6 ... 1.8 1.7 1.7 1.7 1 1.8 2.3 2.5 3.0 2.1 2.3 2 3.3 2.7 4.1 4.6 3.1 3.6 3 5.0 3.7 5.9 6.4 4.7 5.1 4 6.8 5.4 8.4 9.1 6.7 7.3 5 8.6 6.9 10.7 11.2 9.5 9.4 6 10.2 8.9 12.8 13.0 10.9 11.2 7 12.1 11.4 14.5 13.6 12.3 12.8 8 13.5 12.9 15.3 14.5 13.3 13.9 9 12.2 13.4 15.9 14.9 13.6 14.0 10 12.7 14.0 15.5 15.0 14.0 14.2 11 ... ... ... 15.1 14.4 ... ------+---------+------+---------+------+------+---------+

[1] These weights are not figured in the averages; see text.

Seven nestling Seaside Sparrows and five nestling Sharp-tailed Sparrows were weighed at 24-hour intervals until they left their nests. The birds were weighed in early morning before they had received much food.

Weights of these individuals, and daily averages for each species are shown in Table 1. The weights in the zero column were of nestlings that had not been fed. The weight of one hatchling (1.9 gm.), which does not appear in the table, is included in the average for the zero column.

Two young Seaside Sparrows, approximately a week old, fell out of a nest between 9:30 a.m. July 6 and 5:30 a.m. July 7. When I found them below the nest, at the latter time, their temperatures were far below normal, and they had lost a considerable amount of weight. These abnormally low weights were not figured in the averages. The weights of Sharp-tailed Sparrows 11 days old were obtained by confining the birds to the vicinity of the nest with a screen.

[Ill.u.s.tration: FIG. 1. The development of the young of Seaside Sparrows (solid line) and Sharp-tailed Sparrows (dotted line) as evidenced by four linear measurements taken at 24 hour intervals.]

At hatching and throughout nestling life and post nestling life Seaside Sparrows average heavier than Sharp-tailed Sparrows of comparable age (Table 1). Weights of adults of the two species that were netted or collected between May 6 and June 27, 1955, within two miles of Chadwick, Ocean County, New Jersey, follow: Fourteen males of _Ammospiza maritima_ averaged 24.2 gm. (21.9-27.4 gm.); three females averaged 22.3 gm. (19.8-24.4 gm.). Thirty-three males of _A.

caudacuta_ averaged 20.7 gm. (18.0-23.1, 25.8 gm.); 14 females averaged 17.8 gm. (15.3-19.0 gm.), 2.9 gm. less than the males. One female Sharp-tailed Sparrow, weighing 23.1 gm., was not included in the averages because it had an egg with sh.e.l.l in the oviduct.

Montagna (1940:195-196) weighed a series of breeding Sharp-tailed Sparrows (21 males; 5 females) from Popham Beach, Maine, and found the males to be only 0.2 gm. heavier than the females, but he stated that the small number of females weighed, and the high percentage of these that contained eggs, probably lessened the difference in weight found at other seasons.

The four linear measurements that I took on the same series of adults confirmed the size difference: Seaside Sparrows average larger than Sharp-tailed Sparrows, and males average larger than females in both species. The average and range for each measurement taken on the sparrows is presented in Table 2.

Four linear measurements were also taken daily on the young sparrows. A summary of these data appears in Figure 1.

_Behavior_

The first indication of hatching is a crack in the side of the egg along the line of greatest circ.u.mference. The crack is extended along this line by the egg tooth, and then contraction of muscles of the neck by the embryo separates the sh.e.l.l into two pieces. Extension of the legs frees the bird from the sh.e.l.l. I held the eggs of two Seaside Sparrows in my hand and watched this procedure. In each instance the young bird defecated in the sh.e.l.l before freeing itself. A barely audible "peep" note was heard from one hatchling Sharp-tailed Sparrow when I held it near my ear. When free from the sh.e.l.l, the young birds rest on their tarsi, abdomen and forehead; their down dries in a few minutes, and their skin becomes noticeably darker. One sparrow gaped five minutes after hatching and all the young gaped later the same day.

The abdomen of the young becomes distended when they are fed by the parents.

[Ill.u.s.tration: PLATE 5

_Ammospiza caudacuta_

_Ammospiza maritima_

Drawings of the nestlings of the two species of _Ammospiza_ approximately three days of age showing the variation in the amount and placement of the neossoptiles in the two species. Abbreviations for feather tracts in which downs were found: ca, capital; h, humeral; a, alar; d, d?, dorsal; cr, crural; v, ventral.]

[Ill.u.s.tration: PLATE 6

An aerial view of the marshes at Chadwick (upper left) and Lavallette (lower left). The Atlantic Ocean appears in the upper right of this photograph.]

TABLE 2--LINEAR MEASUREMENTS IN MILLIMETERS OF ADULT SEASIDE SPARROWS AND SHARP-TAILED SPARROWS CAPTURED OR COLLECTED WITHIN TWO MILES OF CHADWICK, OCEAN COUNTY, NEW JERSEY, BETWEEN MAY 6 AND JUNE 27, 1955.

========================================================= _Ammospiza maritima_ --------------+-------------------+---------------------+ 14 males 3 females --------------+-------------------+---------------------+ wing (chord) 64.14 (60-66) 58.33 (58-59) tail 55.28 (54-59) 51.00 (49-53) tarsus 23.00 (22-25) 22.17 (21-23) culmen 15.18 (15-15.5) 14.50 (13.5-15.0) --------------------------------------------------------- _Ammospiza caudacuta_ --------------+-------------------+---------------------+ 33 males 15 females --------------+-------------------+---------------------+ wing (chord) 58.79 (55-61) 55.67 (54-58) tail 49.48 (46-53) 46.93 (45-50) tarsus 20.91 (20-22) 20.30 (20-21) culmen 13.67 (13-14) 13.23 (12.5-14.0) --------------+-------------------+---------------------+

In the first 24-hour period after hatching the soft "peep" note is heard frequently. The young are better able to right themselves, and many feather papillae show distinctly through the skin.

On the second day young are capable of moving short distances by using their wings and feet. A thick ridge of tissue forms over the eyeball where the eyelids later delaminate. The call is now a double version of the "peep" note described above.

When the young are three days old the eyelids open, but only slightly.

In the next three days the young become better co-ordinated and the eyes open fully. The egg tooth was last seen on a young bird on the sixth day. All incoming feathers remain sheathed until the seventh day.

On the seventh day young show the first signs of cowering. Previously, they all begged when I came to the nest. The remiges remain sheathed, but the body feathers emerge from the tips of the sheaths. A quiet reedy call replaces the "peep" note. A quiet, but squealing distress call was also first noted on the seventh day, when the young were handled.

On the eighth day the remigial sheaths become gray (previously they were dark blue) and begin to slough off. When removed from the nest, the young attempt to escape. Begging is less frequent and cowering is the predominant att.i.tude towards intruders.

The first young of both species left the nest on the ninth day. It must be remembered, however, that this remark, and succeeding remarks, concerning departure of young from nests pertains to young that were disturbed daily by me. The others climbed to the edge of the nest when they were left alone, but remained in the nest when they were all replaced. Gaping was recorded once on the ninth day. Stuart W. John watched two Sharp-tailed Sparrows on my study area leave a nest. They climbed out and immediately hid in a tussock of gra.s.s a few inches behind the nest.

On the tenth day when I parted the branches over one Seaside Sparrow nest, the four young jumped from the nest and scattered in the gra.s.s.

One of these birds gave a chipping note similar to the distress call of adults. No bird remained in a nest longer than ten days. Four young left the nest after nine days, seven young left on the tenth day. When the young leave the nest they are able to run rapidly through the dense gra.s.s. The young are fed by the parents for approximately 20 days after they leave the nest. Twenty-three days after one young Seaside Sparrow left the nest it was netted at the opposite end of the island, 300 yards from the territory of its parents.

Young Seaside Sparrows fly in an uncertain but characteristic manner when they are flushed from the gra.s.s. They dive clumsily into the gra.s.s after a short flight, making it easy to identify them as birds of the year.

The plumage of sparrows of the Genus _Ammospiza_ serves to conceal them in their habitat. In juvenal and adult plumage, the Sharp-tailed Sparrow is a brown-backed, streaked bird, the color and pattern blending with the matted gra.s.ses (Allen, 1925:67) where the species feeds and nests. The Seaside Sparrow, as an adult, is olive-gray. Its color corresponds to that of the substratum where the species forages.

The juvenal plumage of the Seaside Sparrow resembles that of the Sharp-tailed Sparrow. I believe that young Seaside Sparrows have this brown, streaked plumage because they spend most of their time in the dense gra.s.s. In the Seaside Sparrow a complete post-juvenal molt begins in late August. The resulting plumage resembles that which is acquired by the adults when they complete their post-nuptial molt (Dwight, 1900:192-193).

FOOD, FEEDING, AND CARE OF THE YOUNG

The food habits of Seaside Sparrows and Sharp-tailed Sparrows have been studied by Judd (1901:64-66), who concluded that both species are highly insectivorous. In 51 stomachs of Sharp-tailed Sparrows 81 per cent of the contents was animal. The results of investigation of stomachs of Seaside Sparrows were similar. In each of the two species the bill is more elongated and less conical than in other sparrows. For the two species studied, the shape of the bill seems to be an adaptation for feeding on insects.

When searching for food, Sharp-tailed Sparrows walk through the dense black gra.s.s, deftly brushing stems aside with their bill as they go.

Open areas are generally traversed by rapid running. I never noticed either species hopping. They stop to investigate openings in the matted understory of gra.s.s, often sticking their heads into the holes. Many times I saw these sparrows stretch or jump to pick insects from stems.

Many droppings, almost certainly those of Sharp-tailed Sparrows, were present in areas of damp, matted gra.s.s. Females, when feeding young, obtain most of the food near the nest; several times I saw birds catch insects when they were within inches of their nest. Sharp-tailed Sparrows feed also along the banks of pools and creeks, and along the perimeters of marshes. Sharp-tailed Sparrows seem to be less restricted in the types of feeding habitats they can use than are Seaside Sparrows.

Seaside Sparrows always returned to the edge of the marsh to procure food, according to my observations. The birds at Lavallette fed extensively on noctuid moths. In the feeding territories of two pairs of Seaside Sparrows, along the strip of washed-up eel gra.s.s, I found at least 40 wings of these moths. In several instances the four wings of one moth were lying close together in the same relative position in which they had been on the animal. Legs and pieces of thorax were also discarded occasionally. I watched adults take these moths from the stems of the smooth cord-gra.s.s and snip the wings off with their bills.

Moth wings were present in the other feeding territories, but not in so great a quant.i.ty. Once I saw a female return to the nest with a spider in her bill. Spiders were abundant throughout the marsh.

Dwight (1900:193) was surprised that the two species living in the same environment, and therefore suffering equally from abrasion from the coa.r.s.e marsh gra.s.ses, should have a different number of molts per year.

The Sharp-tailed Sparrow has a complete pre-nuptial, as well as a complete postnuptial, molt. The Seaside Sparrow has only a postnuptial molt, the nuptial plumage being acquired by wear. My observations of the feeding habits of the two species indicate that they do not live in precisely the same environment. The Sharp-tailed Sparrow, which has two complete molts annually, generally forages in dense, abrasive vegetation. The Seaside Sparrow, which has but one molt each year, forages in relatively open areas.

Several times I saw adult Seaside Sparrows fly from their nests toward the feeding territories with fecal sacs in their bills. On the feeding grounds, I found several of these sacs discarded near the moth wings. I saw also female Sharp-tailed Sparrows leave their nests with fecal sacs. I did not see sparrows of either species swallow fecal sacs.

One nest, that of a Seaside Sparrow containing four young, became fouled with excrement when the young were nine to ten days old. It is interesting that these young were cared for only by a male, at least for the last four days of nest life, and that one of the young birds died two days before the others left the nest. This male's mate was probably a female that I banded on June 18 (the young left the nest on June 23) and never saw again. A female, whose mate was probably killed by me on June 15, continued to incubate the three eggs until they hatched on June 29, but deserted the nest when the young were two days old. This female was seen again on August 1 more than 500 yards from her nest site on the island immediately north of the study area.

Devotion of parent pa.s.serine birds to the young typically increases with the growth of the young (Nice, 1943:245). This may explain why the mateless female deserted its nest when the young were only two days old, whereas a mateless male continued to care for his six-day-old young. The death of one nestling, and the eventual fouling of his nest may indicate that the job was too much for one adult to perform. The correlation of increasing devotion of the parents with increasing age of the young was further ill.u.s.trated by the distraction display, noted by me, on the part of a pair of Seaside Sparrows on the day their young left the nest. As I lifted the four nine-day-old young from the nest for weighing, they began to give the distress call. This attracted the parents from the feeding area approximately 60 yards away. The two adults ran around on the ground within ten feet of me giving the _tsip_ note and fluttering their wings. Several times the adults flew within a few feet of me, making a vibrating sound with their wings. Although I realized the function of this display, it was distracting nevertheless.

ACKNOWLEDGMENTS

I am indebted to a.s.sistant Professor Harrison B. Tordoff for comments and suggestions throughout the preparation of this ma.n.u.script, and to Mr. Stuart W. John who photographed the birds and the habitat scenes. The aerial photograph of the study island is reproduced with the permission of Fairchild Aerial Surveys, Inc., and the photograph of Lavallette and Chadwick through the kindness of the Lavallette Yacht Club. The drawings were made by Mr. John R. Beeder. Additionally I wish to express my grat.i.tude to Dr. Dean Amadon, Mr. H. Lyman Sindle, and Mr. Lester B. Woolfenden for help and advice in certain aspects of the field work.