Common murres (Uria aalge) are medium-sized seabirds that live along the coasts of the northern Pacific and Atlantic Oceans. They are excellent divers and can reach impressive depths when searching for food. But just how deep do common murres dive? In this article, we’ll examine the evidence and try to answer this question.
Quick Facts on Common Murres
Before looking at diving depths, here are some quick facts about common murres:
- Common murres are also known as common guillemots.
- They are chunky, black and white seabirds with long, pointed beaks.
- Common murres have wings adapted for underwater swimming.
- They nest densely together on narrow cliff ledges.
- Common murres primarily eat small fish, crustaceans and other marine invertebrates.
- They can live 15 years or more in the wild.
Evidence From Tagging Studies
Scientists have attached depth sensors to common murres to directly measure how deep they can dive. These “tagging” studies provide some of the best evidence on murre diving depths. Here are some findings:
- One study in Canada found that common murres can regularly dive to depths of 50-100 m (164-328 ft).
- The maximum dive depth recorded in that study was 181 m (594 ft).
- A tagging study off the coast of Scotland measured murres diving to depths of over 150 m (492 ft).
So tagging studies reveal that common murres are quite capable of diving well over 100 meters in search of prey. But they likely do not surpass about 200 meters very often. Next, let’s look at how long these deep dives last.
Dive Duration
In addition to measuring depth, tags can also record the duration of dives. Some key findings on murre dive duration include:
- The average foraging dive lasts around 75 seconds.
- Most dives are 2 minutes or less.
- Occasionally, murres will make exceptionally long dives of 4-5 minutes.
So while common murres dive quite deep, most of their dives are relatively short. Longer dives are likely aerobically challenging for them. This explains why extremely deep and long dives are rare.
Feeding Behavior and Energetics
What do we know about murre feeding behavior and energetics that could provide more clues into their diving capacities?
- Murres exhibit binge feeding behavior – they may eat over 30 fish in a single dive.
- They are pursuit divers that chase mobile prey like fish and squid.
- The energy costs of diving deeply are high due to hydrodynamic drag.
- Deeper and longer dives require longer recovery times between dives.
The need to capture many fast-moving prey on each dive likely limits their maximum depth and duration. The high energy costs of deep diving also constrain their abilities.
Comparisons With Other Diving Birds
How do common murre diving depths compare with other birds? Here are some examples:
| Bird Species | Maximum Recorded Dive Depth |
|---|---|
| Common murre | 181 m (594 ft) |
| Thick-billed murre | 210 m (689 ft) |
| Razorbill | 120 m (394 ft) |
| Black-legged kittiwake | 70 m (230 ft) |
The data shows that common murres are among the deepest diving seabirds. However, their close relatives the thick-billed murres can dive even deeper. Overall, common murres seem well adapted for frequent dives to 100+ meter depths, even if they only occasionally venture deeper.
Role of Diving in Foraging
Why do common murres dive to such depths? The clear driver is the need to find sufficient food. Here are some key points:
- Diving allows murres to reach food unavailable near the surface.
- Major prey like capelin and sandlance can form dense midwater schools.
- Deep diving expands the murres’ foraging range.
- This is crucial for meeting their high energy requirements.
In essence, deep diving allows common murres to be successful pursuit hunters and meet their dietary needs, especially when prey is scarce near the surface.
Ultimate Limits on Dive Depth
There are likely anatomical and physiological constraints on just how deep common murres can dive. Some potential limiting factors include:
- The strength of their bones and muscles to withstand pressure.
- Oxygen storage and consumption rates.
- Blood hemoglobin affinity for oxygen at high pressures.
- Time needed to clear nitrogen buildup.
The interplay between these factors likely sets the ultimate boundaries on murre diving capacity. They may occasionally push these limits when extremely motivated.
Conclusions
In conclusion, studies show that common murres are impressive divers, regularly plunging to depths of 50-100 m and occasionally reaching over 150 m. Average dive times are short, around 1-2 minutes. Deep dives help murres find the mobile fish and zooplankton they rely on. Comparisons show murres are among the deepest diving seabirds. Ultimately their diving capacity reflects specializations for finding food in the cold, turbulent waters of the northern oceans.
