With a plumage and bill color that sets it apart from other North American gulls, the Heermann’s Gull is highly social. In fact, over 90% of the population of Heermann’s Gulls breeds on a single island off Mexico. Egg collecting was once a major threat to the population, but protection efforts have resulted in a population increase from a once low level.
Heermann’s Gulls don’t typically breed until four years of age, and nesting takes place early in the year in February and March. Only a small area around each nest is defended by a nesting pair. Sometimes multiple pairs will become involved in territorial disputes.
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Description of the Heermann’s Gull
The Heermann’s Gull has a red bill, dark brown upperparts, grayish underparts, a black tail with a white band on the end, and a white trailing edge to dark wings. Length: 19 in. Wingspan: 51 in.
Seasonal change in appearance
Streaked head in winter.
Mostly brownish with darker head. Attains adult plumage by age four.
Fish, crustaceans, and insects.
Forages by flying over water and dipping to the surface, or by stealing food from other birds.
Breeds in western Mexico and winters in coastal California.
Bent Life History
Visit the Bent Life History for extensive additional information on the Heermann’s Gull.
The shape of a bird’s wing is often an indication of its habits and behavior. Fast flying birds have long, pointed wings. Soaring birds have long, broad wings. Different songbirds will have a slightly different wing shape. Some species look so much alike (Empidonax flycatchers) that scientists sometimes use the length of specific feathers to confirm a species’ identification.
- From the top to bottom: adult (outermost primaries still growing in), Sept; second winter, Aug.; and juvenile, Sept.; all from Washington
- From below
Wing images from the University of Puget Sound, Slater Museum of Natural History
If three eggs are laid, the adult may stop incubating the third egg when the other two hatch, or may neglect to brood and feed a third chick.
Courtship feeding takes place when males and females change incubation duties
High whining or laughing calls are given.
- Dark brownish upperparts and red bill are distinctive.
The nest is either a scrape or a mass of plant material placed on the ground.
Color: Bluish-gray with darker markings.
Incubation and fledging:
– Young hatch at about 28 days.
– Young fledge (leave the nest) at about 45 days.
Bent Life History of the Heermann’s Gull
Published by the Smithsonian Institution between the 1920s and the 1950s, the Bent life history series of monographs provide an often colorful description of the birds of North America. Arthur Cleveland Bent was the lead author for the series. The Bent series is a great resource and often includes quotes from early American Ornithologists, including Audubon, Townsend, Wilson, Sutton and many others.
Bent Life History for the Heermann’s Gull – the common name and sub-species reflect the nomenclature in use at the time the description was written.
LARUS HEERMANNI (Cassin)
Among the mixed flocks of large gulls which frequent the beaches of southern California we frequently see a few and sometimes many smaller gulls conspicious by their dark color and long legs. Some seem to be wholly black or dark brown; these are the young birds, which are present more or less all the year round. Others, with conspicuous white heads, are the adults; these are absent during the later part of the spring and early summer, while on their breeding grounds farther south. The species is very well marked and entirely unlike any other species of Larus. It has even been placed by some writers in another genus, Biasipus, together with two or three other species found in other parts of the Pacific Ocean, which its general appearance seems to warrant. It is different from other gulls also in its migrations, being the only one of our gulls which migrates southward to breed and northward again to spend the fall and winter.
Courtship: Mr. Wilmot W. Brown jr., has given us the only account we have of the courtship of this species. He was fortunate enough to arrive on the Island of Ildefonso, in the Gulf of California, early enough to see it. I quote from his notes, published by Col. John E. Thayer (1911), as follows:
When I first arrived (March Z4) there were an immense number of birds. The males were constantly seen fluttering over the females on the ground, near their nests; but no eggs were laid until April 2. It seems they spend some time in courtship before settling down to their matrimonial duties. The female when in passion emits a peculiar squeaky sound as she coaxes the male by squatting (lown and going through the most ludicrous motions. I have also seen a pair holding on to each other’s bills, a kind of tug-of-war affair: then they would back away and go through a suggestion of a dance, hut all the time talking to each other in low love tones. The appearance of a duck-hawk would send them nil flying to sea. They would return, however, very quickly.
On the southeastern end of the island, facing the sea, there Is a large semicircular shaped depression, which covers about 5 acres. It Is quite level on the bottom and covered with gravel, with here and there blocks of lava scattered about. It is well protected from the northwest wind, which prevails here in March and April. At the time I arrived on the Island immense numbers of these gulls had congregated. They literally covered the ground. They were so occupied in their love making that they paid very little attention to us. Their cries deadened the cries of all the other birds, and they kept it up all through the night.
Nesting: The nest in all cases was simply a well-formed depression In the ground with no lining whatsoever. There must have been over 15,000 Heermanns gulls nesting on this island.
Mr. Pingree I. Osburn (1909) found a colony of Heermann’s gulls breeding “on a remote rock off the coast of the State of Jalisco, Mexico, in about the parallel 180 N.” He writes:
The rock was about 25 feet high and 50 by 150 feet across, with a plat of coarse bunch grass a foot high in the center, and along the edge a barren strip of white rock, broken up here and there with crevices and bowiders. The rock contained 31 pairs of breeding birds, ascertained after a careful count. The birds in the nesting grounds behaved in much the same manner as the western gulls, but were tamer, swooping down within a foot of my head and alighting nearby while I was photographing in the colony.
A cursory survey of the rock showed that it was steep on all sides. The birds undoubtedly preferred the level ground for a nesting place, as only one set was found on this cliff. The nests were located usually between bowiders or nestled down In the bunch grass In the center of the rock. Those in the grass were usually well made of sticks, dry grass, and weeds, and sometimes with a slight lining of feathers. They were much better made and more compact than those of the western gull. Several nests in my collection still show their original shape and construction; also retain the strong odor peculiar to these birds on their nesting grounds. A few sets were found with almost no nest; simply a cup-shaped cavity scantily lined with shells and a stick or two. The nests were well scattered about over the rock, no close grouping being evident. The measurements of the nests average, in inches – outside width, 10; depth, 2 1/2. No other species of gull was seen in company with the Ileermann gulls, and none within hundreds of miles of these islands.
The first visit to the rock was on April 11. At this time about one-third of the eggs were heavily incubated. The remainder were in all the lesser stages. The sets contain two and three eggs in about equal numbers, with a possible majority of three.
Eggs: The eggs show the greatest variation in color. The general ground color Is pearl gray with a very slight creamy tinge. In some the ground color Is ashy gray and In others light bluish gray. All the eggs are spotted and blotched, the markings showing no particular rule for location at one end or the other. They have faint lavender spots, which are covered with smaller but more distinct spots of grayish brown, umber, grayish blue, and dark lavender. They are very rarely scratched with fine lines, but occasionally the spots and splashes show a trend to a lengthwise direction. A few examples also have faint wreaths about the large end. Where this occurs the area Inside the wreath Is usually void of heavy markings and decorated only with faint Irregular lavender spots. In extreme examples the eggs range from one egg, which is indistinctly specked with cinnamon brown and marked evenly with faint lavender, to an egg which has a ground color twice as deep as the egg just mendoned, and heavily splotched with dark olive and dark lavender. There is also one set of three which is especially unlike the others, in that the eggs are smaller and more elongated, both ends of the egg being almost identical in shape. This set is differently marked also. The spots are dingy and not clearly defined as in the remainder of the series. In all, they are the handsomest eggs of any species of this genus which I have ever seen.
The measurements of 52 eggs, in various collections, average 59.2 by 42.7 millimeters; the eggs showing the four extremes measure 64 by 45 and 53 by 37.5 millimeters.
Plumages: The downy young is covered with short, thick down, which on the head, throat, breast and flanks is “pinkish buff” or “pale pinkish buff,” becoming paler toward the belly, which is pure white. The back is grayish white, mottled with dusky, and there are a few dusky spots on the top of the head. I have seen no specimens illustrating the change into the first plumage.
Coues (1903) says of the young of the year:
Entire plumage deep sooty or fuliginous-blackish; all the feathers, but especially those of hack and upper wing coverts, edged with grayish-white. Primaries and secondaries black, as in adults, with only traces of white tips on the former. Tail black, very narrowly tipped with dull white.
Birds that I have seen in what I call the juvenal plumage have the greater and lesser wing-coverts and the feather edgings “olive brown.” They apparently change, by a partial and gradual molt, from this into the first winter plumage between June and October, the wing-coverts becoming grayer, the light edgings of the feathers disappearing by wear, and more or less white appearing on the throat and chin. During the first spring the wholly black bill of the young bird becomes dull reddish on the basal half. This plumage is worn until the next summer, the first postnuptial molt, if it may be so called, beginning in June. This complete molt produces the second winter plumage, which is similar to the first winter, except that the primaries and rectrices are blacker and very narrowly edged with pale brown; the upper tail-coverts are more slaty; the head and nape are clear slate-black, the mantle is darker slate-black and the bill is practically like the adult.
A year later the young bird assumes a third winter plumage, similar to that of the winter adult, except that the dark mottling on the head is more extensive, including the whole head and throat, and all the colors are darker. The white predominates on the throat, but the rest of the head is very dark. The wings and tail of the adult plumage are assumed, but there is great individual variation in the extent of the white tips of the primaries and the rectrices, though the latter are always broadly tipped with white. At the next prenuptial molt, which is only partial, including mainly the head and neck, young birds become indistinguishable from adults; they are then nearly 3 years old.
The postnuptial molt of adults, which is complete, occurs mainly in July and August, though it is often prolonged into September. Adults in the fall may be distinguished from young birds by being somewhat lighter in color both above and below, with the gray of the body plumage shading off gradually into the white of the head and neck; in young birds this change is much more abrupt. The head and neck are much whiter in old birds, with much less dusky mottling, confined principally to the top and sides of the head. The partial prenuptial molt begins in December, and by January or February the pure white head of the nuptial plumage has been acquired. The white tips of the primaries wear away partially or wholly before spring, and the white tips of the rectrices also disappear before the postnuptial molt.
Food: Although the food of Heermann’s gull consists largely of fish and other sea food, which it obtains offshore, it also indulges freely in a great variety of other foods and does its part as a scavenger along the shores and on the beaches with the other gulls, where it does not seem to be at all fastidious as to its diet. Dr. George Suckley (1800), however, says:
This species, unlike the ring-billed and many other gulls, does not seem to be fond of feeding on the shores and hare flats, but is almost always (in that vicinity at least) found on the kelp beds floating in the deep water some distance from shore. Whether they are attracted to these kelp beds by the hopes of finding small shellfish in the upturned and netlike roots of such plants as, detached from their fastenings on the bottom, have become entangled together and with others In situ, or because these floating islands afford a convenient resting place where they can rest to a great extent secure from their enemies of the land, I can not say; but presume that the presence of a supply of food must be a great inducement.
Mr. A. W. Anthony (1906) describes their method of catching fish as follows:
When herring are swimming In compact schools near the surface both Hearmann’s and western gulls secure them by approaching the school from behind and flying near the surface of the water, making repeated, quick dips into the school. The fish seek safety In the depths the Instant anything occurs to alarm them, but soon return to the surface, so that the gulls by stalking them from the rear are enabled to approach quite near before the fish are alarmed. As soon as the limits of the school have been passed the gull, rising higher In the air, returns by a wide circuit and again passes over the school from the rear. As the fish all swim In one direction, In a compact mass, these tactics afford the gulls a decided advantage, which seems to be thoroughly understood. I think that the Heermann’s gull secures about one out of five fish that are snapped at and the western half as many. Royal tern and the other gulls employ these same methods but to a less extent.
They have also been found to feed on shrimps and other crustaceans and mollusca.
Behavior: I have never noticed anything peculiar or distinctive in the flight of this species, which is very much like that of the larger gulls; nor can I find anything of interest in regard to it in print The species is, of course, easily recognized in life by its very distinctive colors in all plumages.
Mr. Anthony (1906) refers to its voice as a “whining catlike cry” while attacking the pelicans to rob them of their food. Mr. Osburn (1909) says:
Their cry was an oft-repeated “cow-auk,” “cow-eek,” given when high In the air, and a rapid guttural “caw-ca-ca-ca” when hovering near the nest.
Mr. W. L. Dawson (1909) writes that, if disturbed in their summer loafing places, “they suddenly take to wing and fill the air with low-pitched mellow cries of strange quality and sweetness, as they make off to some distant rendezvous.”:
Though not so much of an egg thief as some other gulls, it is somewhat of a pilferer of food and quite bold in attacking species larger than itself which are too stupid to resist its persecution. Mr. Anthony (1906) has given us the following interesting account of its method of robbing the pelicans:
Heermann’s gull is by far the most active and successful In catching small fish from the surface; but as a rule will seldom attempt to catch his own diner if there are any pelicans among the delegates to the convention. There are times when the herring are so thick and so driven from below by the large fish that the pelicans will sit on the surface and snap them up without plunging, as Is their normal method, from a height of from 10 to 30 feet In the air. If the fish are swimming the deep plunge of ten carries the bird completely under the surface, and when a second later he bobs up like a cork he Is sure of finding at least one, often two Heermann’s gulls expectantly awaiting the result. If there are two they will usually take up stations on each side and but a foot in front of the pelican, which still holds Its huge bill and pouch under the water. It may be that the pelican does not yet know the result of his efforts, for In plunging the pouch Is used as a dip net and, If nothing else, It Is full of water, which is allowed to escape past the loosely closed mandibles until, perhaps 5 or 10 seconds after the bird made his plunge, a flutter is seen in the pouch, announcing one or more struggling victims. It Is still an open question, however, whether they will be eaten by the gull or the pelican, and the latter is seemingly well aware that a herring Ia the gullet is worth two In the pouch, for it will often wait several seconds for a favorable opportunity for disposing of the catch; the gulls meantime constantly uttering their nasal whining note and keeping well within reaching distance of the pouch. When the critical moment arrives the pelican throws the bill up and attempts to swallow the fish, but, with cat-like quickness, one or both gulls make a similar effort, and should the fish In its struggles have thrust Its tall or head past the edges of the mandibles, as very often happens, it is an even chance that the gull gets the prize; in fact, I have often seen a Heermann gull reach well Into the pouch and get away with a fish in the very act of slipping down the throat of the pelican.
I remember a very amusing incident of this nature I once witnessed on the coast of Lower California. The pelican, after securing a herring, “hacked water” until it was supposed to be far enough from its parasite to venture swallowing it, but as the huge bill was tipped up and opened the gull plunged forward and thrust its entire head and neck into the pouch; the pelican, somewhat quicker than most of its kind, closed down with a snap and caught the intruder, which in turn had caught the fish; neither would yield any advantages gained, and for perhaps half a minute the pelican towed the gull about by the head, amid most violent protest from a hundred or more gulls assembled, while other pelicans sat like solemn Judges, perhaps offering to arbitrate the question. At last a more violent twist than usual on the part of the gull freed him from limbo, minus a few feathers, but in no manner daunted, for a moment later it was following closely in the wake of the same pelican, waiting for it to plunge for another fish, and I never did learn which really swallowed the one in controversy.
Dr. E. W. Nelson (1899) observed that “these gulls are bold and noisy aggressors when they wish to take advantage of the gannets, and about the breeding places of the latter they feed largely at the public expense.” One that he shot on Isabel Island, off the west coast of Mexico, had in company with its mate “harried a bluefooted gannet into disgorging a number of small fish upon a rock at the edge of the water, and was picking up the spoils by a series of little downward swoops and hoverings.” Mr. Harold H. Bailey (1906) in the same region, noted similar behavior toward the boobies. He also mentions the following incident:
One day while sitting on a rock in-front of camp at White Rock waiting for lunch, I saw one of a pair of great rufous-bellied kingfishers fishing from a rock about 20 feet farther on. As it returned to its perch from one of its little plunges a Heermann’s gull swooped down and tried to get its food before it could be swallowed. The kingfisher dove to the water and at each descent of the gull, dove below, these tactics being kept up until the gull got disgusted and left.
Winter: At the close of the breeding season the Heermann’s gulls migrate northward along the coast of California and as far north as British Columbia. They have been seen flying north along the coast of Washington as early as July. Adults become abundant on the California coast in July and young birds in August. They are common all winter on the coast of southern California, both adults and young, until the adults migrate south again in the spring to breed.
Breedinq range: Paciflc coast of Mexico. Known to breed in the Gulf of California (Isla Raza and Ildefonso Island), Lower California (Magdalena Bay), on the Tres Marias Islands, and at Mazatlan.
Winter range: Northward in summer along the Pacific coast to northern Washington (Puget Sound), and occasionally to northern Vancouver Island. Southward along the Central American coast to Guatemala (Chiapam and San Jose).
Spring migration: Adults return to their breeding grounds from both northern and southern winter ranges in March.
Fall migration: Northward movement begins in May, reaching southern California about June 1; Monterey, June and July; Farallones, May 20 to June 3; British Columbia, Vancouver Island, June 28. Southward retirement again begins in August, or even July, but last birds do not leave iPuget Sound until October, and few remain in Washington until November. Bulk of the flight passes Monterey in November, but a few birds winter there.
Egg dates: Mexico, west coast: Fifteen records, April 8 to June 17; fourteen records, April 8 to 11.