The Caspian Tern is a large tern found across temperate Eurasia and parts of Australia. It is the largest tern in the world and is known for its size, distinctive plumage, and loud calls. While most bird enthusiasts are familiar with the Caspian Tern’s appearance and behavior, its height and weight are details that require a bit more research to pin down precisely. In this article, we will explore what is known about the typical height and weight of the Caspian Tern to satisfy the curiosity of birders, scientists, and anyone else interested in this magnificent bird.
Quick Facts on Caspian Tern Size
Here are some key facts on the Caspian Tern’s size:
– Average Height: 16-19 inches (41-48 cm)
– Average Weight: 14-23 oz (400-650 g)
– Wingspan: around 4 feet (1.2 m)
– Large, heavy body compared to other terns
– Among the biggest terns in the world
So in summary, the Caspian Tern is generally about 1.5-2 feet tall and weighs just under 2 pounds on average, although size can vary across individuals and subspecies. Their wingspan is their most notable feature, stretching to around 4 feet across in mature birds. Overall they have a very large, robust body compared to related terns.
Typical Height of the Caspian Tern
The typical height of a Caspian Tern measures from around 16-19 inches (41-48 cm). This can vary based on:
Subspecies
There are several recognized subspecies of Caspian Tern that show slight variations in size. On average:
– C.c. caspia: 18-19 in (46–48 cm)
– C.c. tschegrava: 17-18 in (43–46 cm)
– C.c. strenuus: 16-17 in (41-43 cm)
So the nominate C.c. caspia tends to be the largest on average.
Sex
Males tend to measure slightly larger than females in height. Average measurements are:
– Males: 18 in (45 cm)
– Females: 17 in (43 cm)
Geographic location
Size can vary across the Caspian Tern’s wide breeding range. Terns at higher latitudes tend to be larger.
– Larger in Europe
– Smaller in Southeast Asia and Australia
Age
Younger terns are typically shorter than mature adults. Juveniles measure about 2-3 inches shorter than adults.
So while 16-19 inches is typical, the tern’s size depends greatly on specific traits like subspecies, sex, location, and maturity.
Typical Weight of the Caspian Tern
The typical body weight of a Caspian Tern ranges from around 14-23 oz (400-650 g). As with height, weight varies across factors like:
Subspecies
Heavier subspecies:
– C.c. caspia: 20-23 oz (600-650 g)
Lighter subspecies:
– C.c. tschegrava: 16-18 oz (450-500 g)
– C.c. strenuus: 14-16 oz (400-450 g)
Sex
Males average slightly heavier than females:
– Males: 18-20 oz (500-600 g)
– Females: 16-19 oz (450-550 g)
Age
Adults are heavier than juvenile terns.
Condition
Weight fluctuates seasonally as terns lose and gain fat. Terns weigh the most right before migration.
So in their peak condition, a large Caspian Tern can potentially weigh over 20 oz, while a small juvenile may weigh under 16 oz. 14-23 oz covers the typical range across various factors.
Key Features that Add Size
Several physical traits give the Caspian Tern its large and imposing stature:
Large, heavy bill
The thick, heavy orange bill measures around 2 inches long. It helps the tern grasp large prey.
Robust, barrel-shaped body
The body is wide and stout compared to other terns, with broad shoulders and chest.
Long, sturdy legs
Legs are longer than in similar terns at 2-3 inches, helping wade in deeper water.
Dense plumage
Waterproof feathers help retain body heat better than most terns.
Long, pointed wings
Wings measure around 20 inches and appear pointed when folded.
Comparison to Other Terns
The Caspian Tern is much larger than most of its close tern relatives:
Common Tern:
– Height: 13-15 in (33-38 cm)
– Weight: 2-5 oz (60-140 g)
Forster’s Tern
– Height: 14 in (36 cm)
– Weight: 5 oz (150 g)
Royal Tern
– Height: 18-20 in (46-51 cm)
– Weight: 14-20 oz (400-600 g)
So while similar in length to a Royal Tern, the Caspian is stockier and weighs slightly more on average. It dwarfs smaller terns like Common and Forster’s Terns.
Why the Caspian Tern is So Large
The Caspian Tern’s impressive stature provides key advantages:
Foraging advantages
The large bill allows them to capture bigger fish and larger prey than other terns.
Wider breeding range
Their size enables them to breed further north than smaller terns.
Migration
A robust body stores more fat for long migrations and harsh winters.
Thermoregulation
The thick plumage retains heat better for cold northern climates.
Dominance
Large size establishes dominance over breeding/feeding grounds.
So the Caspian Tern’s height and weight seem to be key adaptations related to migration, prey capture, breeding success, and survival in cold climates.
Typical Diet for its Size
The Caspian Tern’s large size enables it to hunt large prey:
– Small fish – anchovies, smelt, sticklebacks
– Large fish – mullet, mackerel, salmon, trout
– Insects
– Small amphibians and crustaceans
An average 4-8 oz (115-230 g) fish provides a good-sized meal. Their large bill also helps capture biting and stinging insects unpalatable to smaller terns.
Overall, the Caspian Tern’s height and weight allow it to regularly consume bigger prey than most related terns.
Growth Rate of Caspian Terns
Caspian Terns grow rapidly from chicks to adults:
Hatchlings
– Weigh 1-2 oz (25-60 g)
– 3-4 in (8-10 cm) long
– Covered in downy feathers
Fledglings (3-4 weeks)
– Weigh 5-7 oz (150-200 g)
– Bill not yet full size
– 7-9 in (18-24 cm) long
– Limited flight ability
Juveniles (2 months)
– 11-13 in (28-34 cm) long
– Weigh around 9-11 oz (260-320 g)
– Bills near adult size
– Able to fly well
Adults (3+ years)
– Full adult size reached
– Weight levels off around 20 oz (600 g)
– Molt and replace feathers periodically
So Caspian Terns are almost fully grown after just 2-3 months, reaching adult size by age 3. Their rapid growth aids survival.
Overview of Caspian Tern Size at Different Ages
| Age | Height | Weight |
| Hatchlings | 3-4 in (8-10 cm) | 1-2 oz (25-60 g) |
| Fledglings | 7-9 in (18-24 cm) | 5-7 oz (150-200 g) |
| Juveniles | 11-13 in (28-34 cm) | 9-11 oz (260-320 g) |
| Adults | 16-19 in (41-48 cm) | 14-23 oz (400-650 g) |
This table summarizes the growth timeline of Caspian Tern chicks into full-grown adults. There is rapid growth in just the first few months until adult size is attained.
Tracking Caspian Tern Chick Growth
When studying Caspian Terns in the wild, researchers will monitor chick growth carefully:
– Weighing chicks periodically after hatching
– Measuring growth of bill, wings, legs, and tail with calipers
– Banding chicks with ID tags to follow individuals
– Comparing growth rates of different chicks
– Recording dates when key growth milestones are reached
– Monitoring feeding rates of chicks by parents
Why Track Growth?
– Ensure colony health and normal development
– Understand impact of environmental factors
– Compare growth at different colonies
– Identify vulnerable chicks for intervention
– Correlate growth with nesting or migration timing
Careful tracking provides valuable data on Caspian Tern biology and the health of the colony. Changes in growth can signal issues with the breeding site habitat, available prey, contamination exposure, or other factors.
How to Measure a Caspian Tern’s Height
When handling a live Caspian Tern, researchers take the following steps to accurately measure height:
Use proper restraint
– Restrain bird gently but securely in hand
– Prevent flapping, twisting, or pecking
– Support body and head
– Partner can assist restraint
Position bird correctly
– Set tern on flat surface like a table
– Ensure legs are straight and flat against surface
– Stretch neck upright but relaxed
– Wings folded in
Use fixed measuring tool
– Ruler
– Measuring tape
– Calipers
Measure from table to top of head
– Read measurement at highest point of head/crown
– Measure a few times for consistency
Proper restraint and positioning are critical for an accurate height reading. Taking multiple measurements ensures the data is reliable.
How to Measure a Caspian Tern’s Weight
To correctly weigh a Caspian Tern, researchers follow these steps:
Use a sturdy scale
– Balance beam scale
– Spring scale
– Digital platform scale
Calibrate scale
– Ensure scale is on flat surface
– Adjust for zero reading before use
Carefully place bird on scale
– Restrain bird properly
– Set gently on scale platform
Read weight display
– Read scale precisely
– Record weight in grams or ounces
– Take several measurements for consistency
Alternate method: bag weighing
– Place bird in breathable bag
– Weigh bag
– Weigh empty bag
– Subtract empty bag weight
Again, taking multiple weight measurements with careful technique ensures accurate data on the tern. With practice, researchers can efficiently weigh many Caspian Terns in a colony.
Conclusion
In summary, the Caspian Tern is the world’s largest tern, typically standing 16-19 inches tall and weighing 14-23 ounces. Exact size varies across different populations, sexes, and ages as these birds grow rapidly from 1-2 ounce chicks to nearly full adult dimensions in just 2-3 months. Their impressive size allows Caspian Terns to capture larger prey, breed further north, migrate long distances, and regulate body temperature better than smaller terns. Researchers carefully measure height and weight of Caspian Terns to track the health and progress of colonies. With accurate data collection, scientists can better understand how the Caspian Tern’s remarkable size enables it to thrive as the world’s largest tern species.
