Why do some predators have so many failed hunts? (1 Viewer)

[Eddie_the_Eagle]

I've been wondering how it happens that in catching food, Peregrines only have a 20% success rate, and according to a study done by someone I can't remember the name of, American kestrels have a 23% success rate when hunting vertebrates, but over 70% when hunting invertebrates. I've come to no conclusions so I'm hoping someone on here might have some ideas. Perhaps as usual there is an obvious reason I have missed. Input would be appreciated.
Eddie

 

[dantheman]

The reward for a successful hunt is a lot. It means it's worth trying again and again until successful.

The reward for a successful hunt on a lesser prey item such as an invertebrate is not so much - only worth doing if success is frequent enough to be worth bothering with.

 

[THE_FERN]

Our another way of looking at it: prey should be difficult to catch as it's its life on the line whereas it's only one meal to the predator. Why are invertebrates easier to catch? Various reasons but one is that the adult stage (which is what birds of prey will be feeding on) is a fraction of the prey's whole life. It is for reproduction mainly: once it's reproduced then in some sense it doesn't "matter" if it gets eaten. Of course, this argument doesn't apply to birds like blue tits which eat large numbers of immature insects.

 

[jurek]

I've been wondering how it happens that in catching food, Peregrines only have a 20% success rate, and according to a study done by someone I can't remember the name of, American kestrels have a 23% success rate when hunting vertebrates, but over 70% when hunting invertebrates. I've come to no conclusions so I'm hoping someone on here might have some ideas. Perhaps as usual there is an obvious reason I have missed. Input would be appreciated.
Eddie

Any Why? question can be answered on several levels of complication in biology.

Here the most obvious is evolutionary: pressure on a predator to get one meal is weaker than pressure on a prey not to lose life. Natural selection stabilizes when the predator is worse at chasing than the prey at escaping.

You can also answer on a behavioral level: a bird of prey usually divides his energy to invest little in any chase. His strategy is to have several opportunities every day and one would win. Like an investor in risky stocks, who does not put all money in one opportunity.

 

[mummymonkey]

Great answers so far. The Red Queen Hypothesis is worth reading.

 

[rosbifs]

Put another way if any predator becomes too successful its population grows to the detriment of its prey which then declines which means the predator has to diversify or die which if the latter leads to a decline...

Its a balance which over time has ups and downs but generally finds a equilibrium.

 

[Eddie_the_Eagle]

jurek, THE_FERN and dantheman have collectively answered my question. Thanks for the other replies too, all interesting stuff.
I was aware of the 'why' in terms of 'to maintain the population balance, the prey should be better at escaping than the predator is at catching'; it was how this is put into practice by the prey (and predator) that I was wondering about. I probably should have said 'how' not 'why'. But I think I get it now.
Good points which hadn't really crossed my mind about invertebrates.

 

[Hauksen]

Hi Eddie,

I've been wondering how it happens that in catching food, Peregrines only have a 20% success rate, and according to a study done by someone I can't remember the name of, American kestrels have a 23% success rate when hunting vertebrates, but over 70% when hunting invertebrates. I've come to no conclusions so I'm hoping someone on here might have some ideas.

Look at it from another perspective: Normally, raptors are so efficient regarding energy expenditure when hunting that they can easily afford the failed attempts and still catch enough prey to feed themselves.

So their strategy doesn't usually try to optimize success rate per hunting attempt, but rather the ratio of energy expenditure to energy intake while maintaining the required total energy intake.

Regards,

Henning

 

[Patudo]

It's partly down to (1) the predator at times attacking half-heartedly and (2) certain types of prey simply being more difficult to catch. Prey abundance in many areas frequented by peregrines is often pretty high and it often happens that they launch a speculative attack trying to surprise prey they think is unwary - "trying it on" as it were. The reward for a successful hunt, especially for prey the size of a pigeon, is high and the cost of failure low; trying five or six times (or more) for such returns is still very much worth the trouble.

Even if the predator is fully motivated - and there can be a tremendous difference in the manner of flight of such a bird (and the difficulty of target it is prepared to take on, etc) compared to one making a speculative attack - prey have their own natural defenses. Even a pursuer as fast and capable as a peregrine will all too easily fail if detected too early, and I've seen pigeons get away many a time even when I thought the attacking falcon had achieved the element of surprise, often via a snap roll at the very last moment. Even when the initial attack takes place high in the air and the cover of the rooftops or trees may be 300 feet or more below, many pigeons not only dodge aside from the first attack but shift away from a second, third or even fourth attempt as both birds are plunging vertically downwards.

The ability and agility of both prey and predator in these and many other situations never ceases to amaze me. Even juvenile hobbies catch dragonflies on the wing with relative ease, yet imagine trying to catch a dragonfly by hand yourself!

 

[Andrea Collins]

A few personal observations of Peregrines hunting, one from yesterday, one from autumn 2019 and a couple of older ones.

Yesterday's was quite amusing. A first winter Peregrine was sitting on the mudflats at the south end of Walney Island, Cumbria. There were lots of small waders about and a few gulls. After a while the young falcon set off across the mudflats at low level. As it approached an adult Herring Gull which was standing on the mud, it suddenly changed direction and accelerated directly towards it.

The Herring Gull seemed to be caught unawares by the Peregrine's approach, stumbled momentarily, spread its wings, then settled again as the falcon passed just above it. Much to my surprise, the Peregrine then turned and accelerated again directly towards the gull in a head on approach. I know Peregrines can tackle birds as large as Herring Gulls with a surprise attack but this seemed a bit risky. This time the gull merely ducked and the falcon gave up and landed further away on the saltmarsh.

Maybe the young falcon wasn't having any luck with the small waders which can be particularly fast and agile and was getting somewhat desperate. Maybe it just had a lot to learn.

The autumn 2019 observation involved an adult Peregrine stooping into a large flock of (Red Knot) on my local river estuary, the Duddon in Cumbria. Having missed all potential targets, the falcon set off in pursuit of one individual Knot. In level flight however, the odds seemed to be in the Knot's favour. It survived three near misses then played its trump card which was to begin climbing steeply until it was a tiny dot in the sky. The Peregrine seemed to know that it wouldn't be able to match the Knot's speed in a steep climb and gave up immediately.

Two other notable observations involved Peregrines chasing a Kingfisher and a (Black-legged) Kittiwake. On both occasions the potential prey made a desperate last ditch attempt to escape by plunge diving into the river estuary/sea. Both escape attempts were successful and the falcons gave up.

It seems it's pretty hard being a top predator when your dinner really doesn't want to be caught. Very entertaining for bird watchers though. I don't think I've ever seen a Peregrine catch anything though obviously they do.

 

[ericmonroe]

I cant understand the difference between vertebrates and invertebrates in this case.

 

[Nutcracker]

Yesterday's was quite amusing. A first winter Peregrine was sitting on the mudflats at the south end of Walney Island, Cumbria. There were lots of small waders about and a few gulls. After a while the young falcon set off across the mudflats at low level. As it approached an adult Herring Gull which was standing on the mud, it suddenly changed direction and accelerated directly towards it.

The Herring Gull seemed to be caught unawares by the Peregrine's approach, stumbled momentarily, spread its wings, then settled again as the falcon passed just above it. Much to my surprise, the Peregrine then turned and accelerated again directly towards the gull in a head on approach. I know Peregrines can tackle birds as large as Herring Gulls with a surprise attack but this seemed a bit risky. This time the gull merely ducked and the falcon gave up and landed further away on the saltmarsh.

Young Peregrines often have eyes bigger than their bellies, or self-belief far better than their abilities. Once saw a young Peregrine hassling a Grey Heron - needless to say, it didn't succeed (!) though it did manage to avoid being impaled. Their failure rate is high, and their survival rate low, in their first winter. The ones that make it learn to do far better, of course.

 

[erinamiles]

I cant understand the difference between vertebrates and invertebrates in this case. I found only this review https://differencebtwn.com/difference-between-vertebrates-vs-invertebrates

Vertebrates are animals characterized by a well-advanced and defined internal skeletal system for different functions, including a structured backbone.
Invertebrates are animals that are characterized basically by lack of backbones and proper skeletal or nervous systems.

 

[Patudo]

Peregrines will also often mob/harass other largish birds - which can be mistaken for genuine attacks, as they can let rip with a good degree of venom, but if the target is something large and ornery like a large gull, heron or even a crow, is almost always pure harassment. The large gulls especially, but also crows, often attempt to hassle peregrines with prey - often just trying it on, but I have seen one instance where a female peregrine was forced to drop her prey - so I guess the peregrine has an incentive to return the favour sometimes.

That said I recall a study that found herring/lesser black-backed gulls made up close to 10% of prey by weight of peregrines on Lundy Island - so they clearly do at times take larger prey. It'd be interesting to know how these were taken, and whether both birds of a pair were involved in the hunt, etc. Perhaps someone who has seen this behaviour could weigh in...

 

[nebli]

A few personal observations of Peregrines hunting, one from yesterday, one from autumn 2019 and a couple of older ones.

Yesterday's was quite amusing. A first winter Peregrine was sitting on the mudflats at the south end of Walney Island, Cumbria. There were lots of small waders about and a few gulls. After a while the young falcon set off across the mudflats at low level. As it approached an adult Herring Gull which was standing on the mud, it suddenly changed direction and accelerated directly towards it.

The Herring Gull seemed to be caught unawares by the Peregrine's approach, stumbled momentarily, spread its wings, then settled again as the falcon passed just above it. Much to my surprise, the Peregrine then turned and accelerated again directly towards the gull in a head on approach. I know Peregrines can tackle birds as large as Herring Gulls with a surprise attack but this seemed a bit risky. This time the gull merely ducked and the falcon gave up and landed further away on the saltmarsh.

Maybe the young falcon wasn't having any luck with the small waders which can be particularly fast and agile and was getting somewhat desperate. Maybe it just had a lot to learn.

The autumn 2019 observation involved an adult Peregrine stooping into a large flock of (Red Knot) on my local river estuary, the Duddon in Cumbria. Having missed all potential targets, the falcon set off in pursuit of one individual Knot. In level flight however, the odds seemed to be in the Knot's favour. It survived three near misses then played its trump card which was to begin climbing steeply until it was a tiny dot in the sky. The Peregrine seemed to know that it wouldn't be able to match the Knot's speed in a steep climb and gave up immediately.

Two other notable observations involved Peregrines chasing a Kingfisher and a (Black-legged) Kittiwake. On both occasions the potential prey made a desperate last ditch attempt to escape by plunge diving into the river estuary/sea. Both escape attempts were successful and the falcons gave up.

It seems it's pretty hard being a top predator when your dinner really doesn't want to be caught. Very entertaining for bird watchers though. I don't think I've ever seen a Peregrine catch anything though obviously they do.

they just need to be successfull once.

 

[nebli]

Young Peregrines often have eyes bigger than their bellies, or self-belief far better than their abilities. Once saw a young Peregrine hassling a Grey Heron - needless to say, it didn't succeed (!) though it did manage to avoid being impaled. Their failure rate is high, and their survival rate low, in their first winter. The ones that make it learn to do far better, of course.

there is a case reported of an adult peregrine male killing at the first stroke a Grey heron in flight just received theblow on the head and that was it

 

[Andy Lakin]

Was watching a distant Peregrine sat on top of a pylon last week and was wondering how much advantage this gave it over its prey. You would think it's success rate would be very high. I'm thinking that the pigeons it was hunting are a lot more agile than they appear. Also why do captors usually appear to be very wasteful when devouring prey? On a side note has anyone got any ideas on wether the white feral pigeons are taken more frequently, as obviously they stand out like a sore thumb (at least to the human eye).

 

[Sterngucker]

I cant understand the difference between vertebrates and invertebrates in this case.

Vertebrates: for example cows, sheep, dogs, rats, snakes and most people ... living things with a spinal column
Invertebrates: for example spiders, octopusses, snails, insects ... living things without a spinal column that are not plants (a cauliflower has no spinal column, but is also not an invertebrate)

 

[Patudo]

Was watching a distant Peregrine sat on top of a pylon last week and was wondering how much advantage this gave it over its prey.

My suspicion (hunting from high perches is how a lot of the birds in my area hunt) is that the real advantage it gives is in spotting prey and probably in planning an approach route to enable maximum surprise. Although they build up some speed when launching themselves from, or simply dropping off a high point, a lot of the time the target they are after is far enough away that any initial assistance in terms of momentum would have long gone.

Feral pigeons are not only more agile than a lot of folks think, but often also very alert and use the terrain to their advantage. I've watched pigeons flying out many a time and some flocks, hugging the rooftops and hurrying along at top speed, seem almost uncatchable - those are the ones you feel the peregrines won't even bother trying. Even when they are flying out higher and not so quickly, you'll see experienced pigeons don't fly in a straight line but make little weaves and changes of direction so that with the wide field of view they have with their eyes being on the sides of their heads, they can "check their six". The moment a peregrine gets too close it's straight down to the rooftops and once a pigeon is too close to the rooftops it's safe.

Juan, do you get to see wild peregrines much in your area? I was fortunate enough to enjoy some fine flying one year over Bruxelles, from the Place Poelaert.