Terns are seabirds in the family Laridae that are known for their sharp, pointed bills that they use to catch fish and other prey. While many tern species have black or yellow bills, some species do develop orange coloration on their bills during the breeding season.
Royal Tern
One of the most widespread and recognizable terns with an orange bill is the Royal Tern (Thalasseus maximus). During breeding season, the royal tern’s bill turns orange-red with a black tip. This bright coloration likely helps with mating displays. Outside of the breeding season, the royal tern’s large bill is orange-yellow.
Some key facts about the royal tern:
- Found along the coasts of North America, South America, and the Caribbean
- Weighs between 400-600g and has a wingspan around 95-105cm
- Feeds by plunge diving for fish and squid
- Nesting colonies can number in the thousands of pairs
- Lays 1-3 eggs per clutch
- Has a loud, harsh “keer-weenk” call
Elegant Tern
The elegant tern (Thalasseus elegans) is a medium-sized tern with breeding plumage that includes an orange-yellow bill with a black tip. Their bill becomes more gray outside of breeding season.
Some key facts about the elegant tern:
- Found along the coasts of California and Mexico
- Weighs around 325g with a wingspan near 95cm
- Dives for small fish like anchovies, sardines, and smelt
- Nests in large colonies of up to 6000 pairs
- Lays 1-3 eggs per clutch
- Has a loud “kree-kree-kree” call
Sandwich Tern
The sandwich tern (Thalasseus sandvicensis) is named for its very yellow-orange bill with a black tip that resembles a sandwich. They are found along the coasts of Europe, Asia, and North America.
Some quick facts about the sandwich tern:
- Weighs around 325g with a wingspan of 80-95cm
- Catches small fish by plunge diving
- Nests in colonies up to 2500 pairs
- Lays 1-3 eggs per clutch from April-June
- Has a loud “kirri-kirri” call
Cayenne Tern
The Cayenne tern (Thalasseus sandvicensis eurygnathus) is a subspecies of the sandwich tern that breeds off the coast of South America. During breeding season, its bill is orange-yellow with a black tip.
Here are some key facts about the Cayenne tern:
- Weighs around 250-300g
- Wingspan of 80-85cm
- Feeds by plunge diving for fish
- Nests in colonies of up to 200 pairs
- Lays 1-3 eggs from March-May
- Call is a loud “kirri-kirri”
Lesser Crested Tern
The lesser crested tern (Thalasseus bengalensis) is an Old World species found along the coasts of southern Europe, Africa, Arabia, and southern Asia. During breeding season, its orange-yellow bill has a black tip.
Some key facts on the lesser crested tern:
- Weighs 115-170g
- Wingspan around 70-80cm
- Feeds on small fish and squid
- Nests in dense colonies up to 2000 pairs
- Lays 1-2 eggs from April-June
- Loud “kirrick” call
Other Terns with Orange Bills
In addition to the species profiled above, some other terns develop orange bills during the breeding season, including:
- Gull-billed tern
- Greater crested tern
- Roseate tern
- Sooty tern
- Bridled tern
- Aleutian tern
The coloration and bright orange hue helps attract a mate and defend nesting territories. Outside of breeding plumage, these terns’ bills often fade to yellow, gray, or black.
Key Facts About Terns with Orange Bills
Here is a summary of some of the key facts about terns that develop orange bills during breeding season:
- Found globally – species on every continent except Antarctica
- All are seabirds that live along coasts and nest in colonies
- Weigh between 115-600g with wingspans of 70-105cm
- Plunge dive to catch fish, squid, and other prey
- Nest in colonies from 200 to 6000+ pairs
- Clutch size is usually 1-3 eggs
- Breeding season spans March to June depending on species
- Loud, piercing calls used for communication
Discussion
The development of orange bills in breeding terns likely serves an important purpose. The bright coloration helps the birds identify their own species, attract mates, and defend nesting territories in dense colonies. Many terns with orange bills even use specialized bill-pointing or fencing behaviors to communicate aggression and breeding fitness. The orange also makes the black bill tips stand out more, which may help when plunge diving for fish.
Outside of breeding season, the orange hue fades since it is no longer needed. The seasonal shift in bill coloration is controlled by hormonal changes in the birds as they prepare to nest. While the orange is vibrant when present, it arises from soft tissue in the bill and is not due to pigments like carotenoids. The specific physiological mechanisms behind the color change remain under study.
In addition to the species profiled here, other terns also develop some orange or red on their bills during breeding season. The colorful bills help connect terns with their mating partners and offspring when nesting in dense, chaotic colonies with thousands of birds. It serves as a reproductive strategy to maximize their nesting success.
Conclusion
In summary, several tern species develop conspicuously orange bills during the breeding season including the royal, elegant, sandwich, Cayenne, and lesser crested terns. The orange coloration likely serves an important functional purpose in mating behaviors, communication, and offspring recognition when these colonial seabirds nest in dense colonies. Outside of breeding season, the bills generally fade to more muted tones of yellow, gray, or black.
| Species | Location | Wingspan | Weight | Breeding Season | Clutch Size |
|---|---|---|---|---|---|
| Royal Tern | Coasts of the Americas | 95-105cm | 400-600g | April-July | 1-3 eggs |
| Elegant Tern | California and Mexico coasts | Around 95cm | Around 325g | May-June | 1-3 eggs |
| Sandwich Tern | Coasts of Europe, Asia, North America | 80-95cm | Around 325g | April-June | 1-3 eggs |
| Cayenne Tern | South American coasts | 80-85cm | 250-300g | March-May | 1-3 eggs |
| Lesser Crested Tern | Coasts of Europe, Africa, and Asia | 70-80cm | 115-170g | April-June | 1-2 eggs |
This table summarizes some key traits and breeding characteristics of terns that develop orange bills during mating season. Their sizes, geographic ranges, breeding timing, and behaviors show interesting variation across the species profiled here.
Detailed Trait Comparison
To provide more detailed data, here is an expanded table comparing the traits of terns with orange bills during breeding season:
| Species | Wingspan (cm) | Weight (g) | Clutch Size | Incubation (days) | Fledging (days) | Max Age (years) |
|---|---|---|---|---|---|---|
| Royal Tern | 95-105 | 400-600 | 1-3 | 21-25 | 20-30 | 17 |
| Elegant Tern | Around 95 | Around 325 | 1-3 | 21-25 | 21-35 | 15 |
| Sandwich Tern | 80-95 | Around 325 | 1-3 | 22-26 | 28 | 20 |
| Cayenne Tern | 80-85 | 250-300 | 1-3 | 22-24 | 21-28 | 12 |
| Lesser Crested Tern | 70-80 | 115-170 | 1-2 | 22-23 | 21-24 | 15 |
This expanded table lets us compare traits like average wingspan, weight, incubation periods, fledging times, and lifespan across the terns. It highlights some interesting variation in these breeding and life history characteristics between the species.
Geographic Ranges
We can also visualize the geographic breeding ranges of these terns with orange bills using a table:
| Species | Breeding Range |
|---|---|
| Royal Tern | Coasts of North America, South America, Caribbean |
| Elegant Tern | Pacific coast of North America |
| Sandwich Tern | Coasts of Europe, Asia, North America |
| Cayenne Tern | Atlantic coast of South America |
| Lesser Crested Tern | Coasts of southern Europe, Africa, Arabia, southern Asia |
This table summarizes the main coastal breeding ranges of each species during the summer nesting season when orange bill coloration is present. It shows how some species have very restricted ranges, while others are nearly cosmopolitan across continents.
Importance of Orange Bills
The development of bright orange bills by breeding terns likely provides some key benefits:
- Visual signal to attract a mate
- Species recognition in mixed colonies
- Territory defense through pointing and fencing behaviors
- Easier to spot chick bills when provisioning food
- May improve visual contrast when plunge diving
The seasonal shift to orange bill color results from hormonal changes associated with breeding condition. The specific physiological mechanism behind the color change is still being researched. The color arises from soft tissue in the bill and is not due to carotenoid pigments.
Threats and Conservation
Many tern species with orange bills face a variety of conservation threats:
- Habitat loss from coastal development
- Disturbance of nesting colonies
- Pollution and oil spills
- Overfishing of food sources
- Predation by invasive species
- Sea level rise from climate change
Protection and management of breeding colonies is critical. Public education, restricting access, and minimizing disturbances are some important conservation strategies. Maintaining clean, productive marine ecosystems will also help these seabirds thrive.
Case Study: Cayenne Tern Conservation
The Cayenne tern is listed as Near Threatened by the IUCN Red List. These terns nest in colonies along the Atlantic coast of South America. Main threats include:
- Habitat loss in coastal Brazil
- Competition and predation from Kelp Gulls
- Disturbance from humans and vehicles
- Pollution from oil spills
Conservation actions that can help Cayenne terns recover include:
- Protecting breeding colonies through fencing and access limits
- Public education programs to limit disturbances
- Restoration of coastal habitats
- Predator control and exclusion
- Ongoing population monitoring
Targeted conservation programs for the Cayenne tern and other threatened terns with orange bills will be key to ensuring their future survival along the world’s coastlines.
Research Priorities
Some priority research areas that can expand our knowledge of terns with orange bills include:
- Genetic analyses to understand relatedness between populations
- Tracking studies to map migration routes and non-breeding sites
- BANDING STUDIES TO GATHER LIFE HISTORY DATA
- Physiological studies on mechanisms behind seasonal bill color change
- Assessing potential impacts of climate change
- Quantifying effects of pollution on breeding success
- Modeling population dynamics and viability
Filling these key knowledge gaps will provide critical information to guide evidence-based conservation of terns with orange bills into the future.
Conclusion
In summary, several tern species in the genera Thalasseus and others develop conspicuously orange bills during the breeding season. This coloration likely serves an important functional role in mating behaviors and communication when the birds nest in dense colonies. The orange bill color results from hormonal changes associated with breeding condition and serves as an important visual signal. Terns with orange bills face a variety of conservation threats that require protection of breeding habitats and colonies, pollution control, and ecosystem-based management. Research priorities include better understanding the mechanisms behind seasonal bill color change, genetics, migratory connectivity, life history strategies, and modeling climate change impacts. Increased knowledge about terns with orange bills can help guide effective conservation plans to ensure the future survival of these iconic seabirds.
