Heermann’s gulls are medium-sized gulls found along the Pacific coast of North America. Here are some quick interesting facts about these birds:
- They are named after Adolf Bernard Heermann, the German naturalist who first described the species in 1859.
- Their scientific name is Larus heermanni.
- They are sometimes referred to as white-headed gulls or band-tailed gulls.
- Heermann’s gulls breed on islands off Baja California and along the west coast of Mexico.
- Their breeding range extends from Isla Asuncion in Baja California to Islas Tres Marias off Mexico.
- Outside of the breeding season, they are found along the Pacific coast from British Columbia to Mexico.
- They live along the coastlines and rarely move inland.
- Heermann’s gulls feed mostly on marine life, including fish, crabs, mollusks and brine flies.
- They are opportunistic feeders and will also scavenge carrion and human garbage.
- They have gray upperparts, white heads, reddish beaks and pink legs.
Physical Description
Heermann’s gulls are medium in size compared to other gull species. Here are some key physical features:
- They measure around 17-19 inches (43-48 cm) long with a wingspan of 41-46 inches (104-117 cm).
- Adults weigh 280–410 grams on average.
- They have pale gray upperparts and wings.
- Their heads are white in the summer and grayish white in the winter.
- Legs and feet are pink to orange-red in color.
- The beak is reddish with a black tip.
- Juveniles are mottled brownish-gray above and pale below with a dark tail band.
- By their second year, the head becomes increasingly white.
- Adults have a bold black “W” mark across the wings that is visible during flight.
Breeding and Nesting
Heermann’s gulls nest in colonies on offshore islands along the Pacific coast. Here are some interesting facts about their breeding habits:
- The breeding season runs from April to July.
- They nest on low, flat islands with little or no vegetation.
- Nesting territories are small, only about 1-3 feet apart.
- Nests consist of scrapes or shallow depressions lined with vegetation, debris and feathers.
- Females typically lay 2-3 speckled olive, brown or green eggs.
- Incubation lasts around 28 days and both parents take turns incubating.
- Chicks hatch with their eyes open and are able to leave the nest within a couple of days.
- Parents feed the chicks fish, marine invertebrates and scraps.
- Chicks fledge at around 5 weeks old.
Diet
The diet of Heermann’s gulls consists mainly of marine creatures. Here are details on their feeding habits:
- They are opportunistic feeders, eating a variety of prey.
- Fish such as anchovies, sardines and mackerel are a major part of their diet.
- They also eat crabs, shrimp, squid, marine worms and mollusks.
- At their breeding colonies, parents feed chicks small fish like anchovies.
- They often dip down to pick food items off the ocean surface.
- They sometimes steal food from other seabirds or raid their nests.
- Heermann’s gulls will scavenge dead fish and marine animals washed up on shore.
- They often congregate around fishing boats to feed on processing waste.
- In coastal areas, they scavenge at landfills and sewage outflows.
Migration and Range
Heermann’s gulls migrate along the Pacific coast between breeding and wintering areas. Here are some key facts about their migration and range:
- They breed on islands from Baja California to Mexico and winter along the Pacific coast from Canada to Mexico.
- Northern populations migrate south after breeding. Southern birds disperse northward.
- Banded birds have been sighted migrating as far north as British Columbia.
- Post-breeding dispersal occurs from July to November.
- Return migration to breeding areas takes place from February to April.
- During winter, they congregate in harbors and bays from Vancouver Island to Baja California.
- Largest winter concentrations are found around San Francisco Bay and in the Southern California Bight.
- They occur as rare vagrants inland and on the Atlantic coast.
Conservation Status
Heermann’s gulls have a relatively stable global population. Their conservation status is considered of Least Concern:
- Global population estimated at 45,000 to 105,000 mature individuals.
- Population Trend: Decreasing but at a rate of less than 30% over ten years or three generations.
- No current major threats have been identified.
- They may be vulnerable to disturbance, habitat loss and marine pollution at breeding sites.
- They are protected under the Migratory Bird Treaty Act in the U.S. and Canada.
Relationships with Humans
Heermann’s gulls adapt readily to human habitats and activities:
- They thrive around fisheries and readily scavenge waste.
- They congregate at harbors, marinas, piers, offshore oil rigs and other marine structures.
- They frequently nest on man-made structures on offshore islands.
- They are attracted to sewage outflows and garbage dumps.
- Considered a nuisance species at some fish processing plants and nesting sites.
- Overall, tolerant of human disturbance and habitat modification.
Fun Facts
Here are some fun and quirky facts about Heermann’s gulls:
- They are sometimes called “chocolate chip gulls” because of the speckled pattern of their back and wings.
- Their legs vary from pink to bright orange-red in color.
- When migrating, flocks may number in the tens of thousands of birds.
- They are very territorial at breeding colonies, with nests built only a foot or two apart.
- Chicks navigate their way to the water’s edge within hours after hatching.
- They are sociable birds, often resting or roosting in large groups.
- In flight, their black wingtips are connected by a bold white diagonal bar.
- They are resourceful foragers, sometimes dropping hard-shelled prey from heights to crack them open.
Population and Distribution
Heermann’s gulls have a relatively limited distribution centered along the Pacific coast:
- Breeding range limited to western Mexico and the Baja California Peninsula.
- 90% of population breeds at just 10 major nesting colonies.
- Largest colony is on Rasa Island with up to 20,000 pairs.
- Other major colonies occur on islands off western Baja California.
- They are year-round residents on the southern end of their range.
- Northern birds migrate south to Baja California for the winter.
- During winter, approximately 75% occupy the Southern California Bight.
- Pre-breeding dispersal northward occurs up to southwest British Columbia.
This table summarizes the population estimates across their breeding range:
Location | Breeding Population |
---|---|
Isla Rasa, Baja California | 20,000 pairs |
Isla Asuncion, Baja California | 5,500 pairs |
San Martín Island, Baja California | 4,000 pairs |
San Jeronimo Island, Baja California | 3,500 pairs |
San Pedro Mártir Island, Baja California | 3,500 pairs |
San Roque Island, Baja California | 3,000 pairs |
San Benito Islands, Baja California | 2,500 pairs |
Natividad Island, Baja California | 1,000 pairs |
Magdalena Bay Islands, Baja California | 500 pairs |
Isabel Island, Nayarit, Mexico | 1,000 pairs |
Taxonomy
Heermann’s gulls belong to the genus Larus in the family Laridae:
- Kingdom: Animalia
- Phylum: Chordata
- Class: Aves
- Order: Charadriiformes
- Family: Laridae
- Genus: Larus
- Species: Larus heermanni
They were first described by German naturalist Adolf Bernard Heermann in 1859 based on a specimen from San Diego. No subspecies are recognized.
Vocalizations
Heermann’s gulls make a variety of calls and sounds:
- Territorial/alarm call is a rapid, laughing “ke-ke-ke-kek.”
- Begging chicks give a shrill “cheep.”
- Adults have a deep, nasal “ha-ha-ha” alarm/panic call.
- Other calls include barks, mews and rattles.
- Non-vocal sounds include bill-snapping and foot-stamping displays.
The various calls and sounds are associated with courtship, territorial defense, begging, warnings about predators, and communication between paired mates.
Conclusion
In summary, Heermann’s gulls are distinctive medium-sized gulls limited to the Pacific coast of North America. Their year-round range centers on Mexico and California. They thrive in association with human habitats and food sources. Although their numbers are declining, they remain widespread and numerous along the Pacific coast. Heermann’s gulls exhibit interesting breeding behaviors, adaptations and vocalizations worthy of further study and appreciation.