Rooks and Crows
My croquet lawn wit rooks in the adjacent field.
Leatherjackets - twaddle!
Look at almost any lawn care book,website or output by “experts” and they will tell you that Leather Jackets (the grub of the Daddy Longlegs) will devastate your grass. For example - “Leather Jackets eat the live roots so that the grass loses anchorage, loses water and nutrient uptake, turns yellow, then brown and the sward can be lifted like a loose carpet”.
What absolute twaddle! In the many years that I have been involved in Croquet Lawn Maintenance and maintaining my own croquet lawn, I have never seen any evidence of Leather Jacket damage to grass plants. The only damage is secondary and caused by outside agents ie Rooks and Crows that dig 50p sized holes to get at the grubs. This is supported by The Turf Growers Association who say ““in most cases the larvae will have no long-term effect on a lawn”.
AI models including ChatGPT are, of course, infected by this rubbish BUT when I challenged it to provide proof of its claims, it couldn’t. The problem is that incorrect information is taught to groundsmen, it is written into books and internet websites and spreads everywhere..
Leatherjacket damage - Rooks and Crows
For many clubs, the first visible sign of trouble is not the grubs themselves but birds – especially rooks – digging up the turf. The birds are doing what rooks do best: exploiting a rich food source. Unfortunately, the result for the club can be an expanse of divots and scruffy scars where there was once a proud, smooth surface.
On my own croquet lawn I tried a technological solution. Isotronic bird scarers were installed on one side of the croquet lawn. The devices worked. After a period of use, the scarers were removed – and, intriguingly, the rooks did not return to the lawn. They continued to feed quite happily in the adjacent field over the hedge, but they seemed to treat the croquet lawn as a no-go area.
A similar pattern occurred in Rookery Wood 300 yards away from my house here in Great Dunham. Twenty years ago, the owner of the wood decided to shoot the rooks. As a result, the remaining colony abandoned the wood and re-established in nearby trees a hundred yards away. It is quite bizarre because he sold the wood shortly after that and despite this, after twenty years the rooks have not returned to Rookery Wood.
What is going on here? Are rooks really capable of this kind of long-term avoidance and “passed-down” memory?
Rooks are highly social, highly vocal and live in dense colonies where information spreads rapidly. Research on rook calls confirms that their vocal communication is flexible and strongly shaped by social context – exactly the kind of system you would expect to carry messages like “that place is dangerous, avoid it”.
Guidance from the British Trust for Ornithology notes that shooting at established colonies tends to lead to dispersal, with birds abandoning large rookeries and re-nesting in smaller, scattered groups over a wider area. Once a site has been heavily disturbed, it may remain unused for many years, even when formal control ceases.
So what can clubs realistically take from this?
1. Strong initial deterrence can have long-lasting effectsA period of consistent, effective deterrence – such as Isotronic scarers or human presence may be enough to convince the resident rook flock that this particular lawn is not worth the risk. Once the birds have built that association and passed it on socially, the pressure on the lawn seems to stay low even after the visible deterrents are removed.
2. Consistency and timing matterBecause corvids are quick learners, mixed messages can undermine control. Allowing birds to feed undisturbed on some days and then trying to frighten them off on others may simply teach them to exploit the quiet times. Deterrence is most effective if it is:
Look at almost any lawn care book,website or output by “experts” and they will tell you that Leather Jackets (the grub of the Daddy Longlegs) will devastate your grass. For example - “Leather Jackets eat the live roots so that the grass loses anchorage, loses water and nutrient uptake, turns yellow, then brown and the sward can be lifted like a loose carpet”.
What absolute twaddle! In the many years that I have been involved in Croquet Lawn Maintenance and maintaining my own croquet lawn, I have never seen any evidence of Leather Jacket damage to grass plants. The only damage is secondary and caused by outside agents ie Rooks and Crows that dig 50p sized holes to get at the grubs. This is supported by The Turf Growers Association who say ““in most cases the larvae will have no long-term effect on a lawn”.
AI models including ChatGPT are, of course, infected by this rubbish BUT when I challenged it to provide proof of its claims, it couldn’t. The problem is that incorrect information is taught to groundsmen, it is written into books and internet websites and spreads everywhere..
Leatherjacket damage - Rooks and Crows
For many clubs, the first visible sign of trouble is not the grubs themselves but birds – especially rooks – digging up the turf. The birds are doing what rooks do best: exploiting a rich food source. Unfortunately, the result for the club can be an expanse of divots and scruffy scars where there was once a proud, smooth surface.
On my own croquet lawn I tried a technological solution. Isotronic bird scarers were installed on one side of the croquet lawn. The devices worked. After a period of use, the scarers were removed – and, intriguingly, the rooks did not return to the lawn. They continued to feed quite happily in the adjacent field over the hedge, but they seemed to treat the croquet lawn as a no-go area.
A similar pattern occurred in Rookery Wood 300 yards away from my house here in Great Dunham. Twenty years ago, the owner of the wood decided to shoot the rooks. As a result, the remaining colony abandoned the wood and re-established in nearby trees a hundred yards away. It is quite bizarre because he sold the wood shortly after that and despite this, after twenty years the rooks have not returned to Rookery Wood.
What is going on here? Are rooks really capable of this kind of long-term avoidance and “passed-down” memory?
Rooks are highly social, highly vocal and live in dense colonies where information spreads rapidly. Research on rook calls confirms that their vocal communication is flexible and strongly shaped by social context – exactly the kind of system you would expect to carry messages like “that place is dangerous, avoid it”.
Guidance from the British Trust for Ornithology notes that shooting at established colonies tends to lead to dispersal, with birds abandoning large rookeries and re-nesting in smaller, scattered groups over a wider area. Once a site has been heavily disturbed, it may remain unused for many years, even when formal control ceases.
- Corvids quickly learn where serious danger occurs.
- They share that knowledge within the group through alarm calls and social learning.
- Their decisions about where to feed or nest can remain altered for many years, creating something like a “cultural map” of safe and unsafe places.
So what can clubs realistically take from this?
1. Strong initial deterrence can have long-lasting effectsA period of consistent, effective deterrence – such as Isotronic scarers or human presence may be enough to convince the resident rook flock that this particular lawn is not worth the risk. Once the birds have built that association and passed it on socially, the pressure on the lawn seems to stay low even after the visible deterrents are removed.
2. Consistency and timing matterBecause corvids are quick learners, mixed messages can undermine control. Allowing birds to feed undisturbed on some days and then trying to frighten them off on others may simply teach them to exploit the quiet times. Deterrence is most effective if it is:
- Prompt – used as soon as damage begins.
- Consistent – the lawn feels risky every time they attempt to feed.
- Focused on key periods – for example, when leatherjacket damage is at its peak and rooks are actively grubbing.
