bird kills

August 18 2025

Report to 31 July 2025

ashleyriver banded dotterel, bird kills, black billed gulls, black-billed gulls, black-fronted tern, management, nesting, rats, weeds, wrybill

Since the end of February work has been ongoing to compile and interpret the results of the 2024-2025 nesting season. Much of this has been on the black-fronted tern.

This season 228 black-fronted tern (BFT) nests were found in 9 colonies – this is a record number of nests and colonies. However, only 25% of nests hatched chicks, but surprisingly the fledgling rate per nest was almost the same – at 25%. The chart below gives a breakdown of nesting outcomes – abandonment was the main problem. Sometimes this could be attributed to a particular cause, other times the cause was completely unknown. A flood in October took away two colonies just as they were developing, but renesting took place at these sites. The most damaging predator was cats – they killed at least 3 adults and a number of chicks, ate eggs and caused desertion of nests. One small colony was entirely wiped out by Norway rats (top graph).

Fledgling success really needs to be calculated by pair nesting on the river not just by nest as presumably birds that lose nests early in the season renest on this river. If the maximum number of nests present at one time is used, or the number of birds counted in our annual survey (with allowance for non-breeding adults) then the fledgling success becomes about 40%. This is probably still not a sustainable rate. The chart below shows a timeline of colonies throughout the year.

For wrybill, 18 nests were found or their locations inferred with some accuracy. The hatching success of these was good with only one flooded, one adult killed by a cat and one losing eggs to a cat. The outcome from one nest was unknown. There were 3 very late nests, perhaps from birds that lost nests in another river.

Fledgling success may have been poor. This has yet to be properly compiled, but it seemed as if many chicks and even fledglings were lost before they left the river.

We only monitor wrybill, black-fronted terns and black-billed gulls in detail. This year the latter didn’t nest in our main area of operations – between SH1 and the Okuku junction.

Predator Catch

The chart below shows predator catch rate along the river since our records began in 2004. Catch rate from 1 August 2024 to end July 2025 was about 0.61 compared to 0.82 the year before and 0.76 in 2022 – 2023. Much of the decline is of ship rats, which don’t threaten river-nesting birds. It is unlikely that our trapping is behind this decline. But there has been a decline in Norway rat catch, this is quite possible attributable to targeting them where they live and feed – mainly by the use of a detection dog. Our kill traps for cats are quite ineffective and we don’t currently have resources to do much live capture – which is massively more successful. Our catch data doesn’t give a realistic picture of the cat problem.

Catch rate for our estuary traps has not declined.

We currently have 27 trappers checking lines along the river or around the estuary with oversight and coordination at this stage by one of the volunteer trappers.

Weed Control at Nesting Areas

In 2024-2025 we successfully predicted BFT nesting areas with 6/9 cleared islands used. Success was partly due to the river not changing since the previous season. Weed growth in some of these places wasn’t extreme –the birds may well have nested here without clearing.

A late April/early May flood cleared all potential nesting areas of weed and control of lupin etc isn’t necessary for the coming season. However, willow seedlings, both purple and crack varieties, are a problem and 4 weeks was spent mapping them–mainly along the edge of braids. ECan sprayed some of this and some was washed away or covered up by the flood. We understand ECan will be doing more spraying of seedlings and source trees in Spring.

Four probable nesting sites need new channels dug to create islands. Gravel extractors at three of these locations have been approached and ECan Braided River Revival team will be coordinating, with the use of a new consent allowing diversions.

Education and Advocacy

May – a productive presentation to the AGM of North Canterbury Branch of Forest and Bird
May – Young writer’s competition highlighting the river estuary at Waikuku
June – Visit and talk to 2 North Canterbury schools
July – Braided Rivers Seminar, G Davey spoke to 160 participants on “Where Ashley River Birds Nest”
July – after the Braid Seminar, ARRG was also represented at a Black Fronted Tern workshop, aiming to coordinate efforts to save this species
August – talk to Waimakariri Combined Friendship Club
August – ARRG involved in Waimakariri District Council led events to welcome the birds back to the river

May 25 2024

Dead Animals

ashleyriver bird kills, black billed gulls, black-billed gulls, black-fronted tern, cats, Predators, rats, trail cameras, Trapping

Report from Grant Davey

About three weeks ago we found a place on the north bank of the river about a kilometre downstream from Ashley Village where several dead sheep (top image) and the remains of a butchered cattle beast had recently been dropped. Immediately beside this, in a ditch, were the jumbled-up remains of dead pigs and deer – they had been there for some months by the looks of them. Less than a hundred metres downstream were the recently deposited remains of a pig.

Jumbled remains of pigs and deer a few metres from where the sheep were found. The rat burrow is right beside this.

This area has been a favourite dropping area for dead animals for years. Recently I’ve found several other dead animals in the general area. Another popular dumping place is the north bank of the river just upstream from the Cones Road bridge. A local shooting competition causes lots of dead animals to be dropped although I don’t know if this competition still happens. Other ARRG trappers report the remains of pigs and deer being dropped on both sides of the river 6 or 7km upstream from Rangiora. The entire berm of course remains a dumping ground for all sorts of things. Yesterday I found a mattress and several areas where people had dropped some sort of bricks, and of course garden clippings etc.

The main issue with ARRG about this disgusting practice is that these dead animals are an important food source for the predators which attack the breeding birds out on the river. The 3 worst predators (Norway rats, cats and harriers) are sustained outside the nesting season by this practice. Trail cameras showed a feral cat with her 3 kittens eating the dead animals which had been recently deposited.

Dead pig a bit further downstream, with the 3 feral cats eating it.

And harriers are constantly there too. There was a recent Norway rat burrow beside the jumbled pig and deer remains, but it was vacant – I think because of all the cat and harrier activity. I’ve put a trail camera there again to see if they turn up.

A harrier at bovine remains which spewed over into the ditch from the recent pile of dead sheep.

This area is about 200m from where late last year we discovered and eventually dealt with a Norway rat colony. We caught 30 rats there, that would be enough to destroy several black-fronted tern colonies. A BFT colony a few hundred metres upstream from here, below the railway bridge, was successful last season, quite possibly because we had dealt to these rats. This rat colony was also at the remains of dead animals. I don’t know how long it was there, but in 2019 there was a massive rat problem at tern and black-billed gull colonies very close by. We lost an entire 48 nest BFT colony and more than a hundred gull chicks to rats. I didn’t have trail cameras there to prove this, but later experience backs this interpretation up. The tern colony was doing fine until rats started appearing in traps within it. In only about 2 nights 2/3 of the tern nests lost all eggs. We now have an ECan funded and organized poisoning programme aimed at rats. The poison was put out by a professional outfit in bait stations. Our trapping programme simply doesn’t work, we need to try other things – hence the dogs and the poison. Hopefully we will see positive results of this, which would be the time to report them.

ECan clean up the worst of the dead animal caches, and did so quickly and effectively with the very bad example found recently. It is something they really don’t like and they have better things to do than clean these messes up.

May 28 2023

Call for control on cats

ashleyriver bird kills, black-fronted tern, cats, management, Predators, trail cameras

Registration, microchipping, limiting numbers per household and desexing of cats is being pushed for by the Ashley Rakahuri Rivercare Group in North Canterbury.

“We do this on behalf of all river inhabitants, particularly braided river birds, and to prevent continuing cruelty to cats which are often abandoned to lead a precarious existence in the wild,” the group said in a letter presented to the Mayor of Waimakariri District Council, Dan Gordon.

Cats were the second worst predator of endangered braided river birds on the river, Norway rats being the worst, the group added.

Operations Manager Grant Davey gave Mr Gordon photographic evidence of cats at nests and traps, some cats had swum across the river.

During a recent trial on baits for traps over three months there were 79 visits of cats, the most of any predator. The traps were not for cats.

Controls would add a layer of protection for endangered birds giving the various species a chance to breed successfully, and the number of unwanted litters would reduce, the group said.

A committee member said: “Bylaws to control cats will, in the long term, lead to fewer cats being dumped and breeding in the wild.

“We know from experience in Canterbury that feral cat populations are huge, and not easily controlled. The cat control bylaws are urgently required.”

The group urged Mr Gordon to go further than the Selwyn District Council bylaw which requires registration and microchipping of cats.

January 19 2021

Gull disturbance

ashleyriver 4X4, bird kills, black billed gulls, black-billed gulls

Over the last few days, we’ve had a number of incidences of 4wds and motorbikes going through the fledgling gulls at the Smarts colony. Around a dozen seem to have been killed.

This year we have had the second biggest black-billed gull colony on the Ashley River in 20 years. The 1,278 nests have produced approximately the same number of fledglings (flying chicks) – this is a very good outcome. We have had no real problem with ground predators with only 2 Norway rats caught in traps in the area and no sign of them killing anything. In a slightly bigger gull colony last year rats killed more than 100 chicks. Also harrier predation has been minimal – perhaps due to pied stilts, black-fronted terns and adult gulls chasing them away. Scarecrows that we placed in the area probably have also helped. Last year harriers also killed more than 100 chicks. Adult gulls have been able to get enough food for their chicks from irrigated farms in the lower Ashley area.

However recently four-wheel drive vehicles and motorbikes have been recklessly driving through young gull chicks. In one case a 4wd was seen to speed up when approaching the birds.

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Most of the chicks can fly and get out of the way to some extent, but at least 10 appear to have been killed.

There are much more vulnerable smaller chicks as well as black-fronted tern and banded dotterel chicks in the area.

There hasn’t been a major amount of damage done, but it is very disappointing to see. Environment Canterbury and the our group have done a lot of work through education, publicity and the installation of signs and physical barriers to stop vehicles getting on the river – this sort of thing should not still be happening.

People should be aware that killing protected native wildlife can result in penalties of up to $100,000 in fines and 2 years in prison. Black-billed gulls have a conservation status of nationally critical.

April 18 2020

Black-fronted Tern and Black-billed Gull colonies, 2019 – 2020 Season

ashleyriver bird kills, black billed gulls, black-billed gulls, black-fronted tern, management, Predators, Trapping, weeds

Summary

(download the full report here)

Two black-billed gull (BBG) and four black-fronted tern (BFT) colonies were monitored over the 2019-2020 season. Another 5 BFT colonies were located but not monitored closely. Colony locations and general outcomes are outlined in the following table:

The main points arising from seasonal observations are:

Breeding

Record number of breeding BBG (1310 nests) – first time since 2000 that 2 colonies located on the river.
Record number of breeding BFT (120 nests).
It is likely that frequent flooding of the Waimakariri river (13km to the south) contributed to the increase in BBG numbers, and possibly the same with BFT.
Despite clearance of weeds from almost 20ha (machine and hand pulling) prior to the season, only one such site (Railway) hosted a gull or tern colony.

Productivity (number of chicks fledged) of both species was poorer than usual.
It appears that predation could have been a major cause of low productivity.

Predation
In addition to the normal all-year-round berm trapping, a total of 48 additional traps were located close to the two BBG colonies and four main BFT colonies during the season.
Norway rats appeared to be the most important land-based predator. At the Railway site, >100 BBG chicks were killed and over 20 BFT nests robbed of eggs (and probably chicks). Norway rats were also the dominant trap-catch within the Groyne 9 BFT colony.
Nine hedgehogs were trapped in a weed-infested area alongside the Groyne 9 colony, but were not caught where there was a water barrier.
Predation did not appear to be a major issue at the Toppings and Groyne 4 colonies.
Harrier hawks accounted for the loss of 116 BBG chicks at the Railway colony.
20 BBG were found dead under powerlines, which they presumably had hit during flight.
The remains of 91 BBG chicks, which most likely died from natural causes, were found within

the Railway colony.

Conclusions

Numbers of breeding BBG and BFT were at record levels, but productivity was average (BBG) or poor (BFT).
Rats and harrier hawks were the main predation dangers, but weed invasion is considered to remain as the biggest long-term threat.

Recommendations

Maintain weed control at the most attractive sites, making use of gravel extraction operations where possible.
Record egg hatch success of BBG and BFT, and Improve techniques for counting chicks.
Initiate predator control earlier at potential colony sites – particularly targeting rats.
Install more trail cameras at colonies, and improve design of run-through traps.
Experiment with harrier hawk deterrents – e.g., strategic use of scarecrows.
Regularly patrol under powerlines to record bird losses to aerial hits.

Download the full report here

February 11 2020

Overhead Line Bird Kill

ashleyriver bird kills spoonbill

It has been long known that some river birds are killed by collision with the overhead lines that cross the Ashley River, but this has not previously been properly documented.

Seven overhead lines cross the river in the area between about a kilometre upstream of the Cones Road bridge and 1.5 kilometres upstream of State Highway One. These consist of 3 pylon lines and 4 normal power lines. Transpower owns the pylon lines and one of the normal power lines; the others appear to be owned by Mainpower.

On 27 January 2019 a number of dead black-billed gulls were found under the power lines 400m upstream from the “Railway” gull colony and 600m downstream from the railway bridge. It was then decided to check the remaining lines; this was done on 29 and 31 January and 4 February. The results are shown in the table and map below. Traverses were done just upstream and downstream from each set of lines and any dead birds within 50m of them should have been located.

Species	Number
Black-billed gull (BBG)	22
Duck	1
Paradise duck	1
Pied oystercatcher (SIPO)	1
Pied stilt	2
Royal spoonbill	2
Total	29

Overhead lines and birds killed

The correlation between overhead line location and dead birds is clear. Dead birds are at times seen elsewhere along the riverbed, but during a bird survey on 31 January from Groyne 2 to the estuary, none were seen other than under the lines. The great majority of bird carcasses were found within 50m of the lines, a SIPO 150m from lines could possibly have died from another cause.

Black-billed gulls are the most abundant species killed by the lines. Four of the 6 BBG beneath or close to the lines just down from the railway bridge were partly eaten juveniles, it is possible that they could have been taken there by harriers, but this does not seem likely. Some of these were partially eaten, but the remains looked more like consistent with being eaten by rats. Under these lines there is vegetation which could host rats.

All but one of the 13 BBG under the lines 400m upstream from the Railway colony were adults, these were intact. These gulls seem to have struck the lines when leaving from or returning to the colony. Each dead adult would probably have resulted in a chick starving to death. Two BBG were found under the westernmost power lines, one was a juvenile with it’s head eaten away. No dead gulls were found under the lines 600m up from the Toppings colony.

Perhaps the most disturbing aspect of the overhead line bird kill is the 2 spoonbill found under the westernmost pylon lines. Spoonbill are normally a very rare sight along the Ashley – but there often seems to be a resident population of around a dozen at the estuary. Nine of these were seen along the upper part of the river on 31 January. They appear to have come up the river to take advantage of easy prey in the shallowing water. The westernmost pylons have a thin wire running along the top – this is much less visible than the transmission wires.

Dead spoonbill beneath pylon lines

Same pylons: note the thin high wire at the top

The dead paradise duck was found under the easternmost pylons on 31 January. It was being eaten by a black-backed gull. On 4 February the only evidence left was a few feathers and some gory stones. Obviously to properly investigate the number of birds killed by lines it will clearly be necessary to check regularly. A male paradise duck was seen under the westernmost pylons, seemingly with an injured wing. However, it was able to fly.

The bird kill needs to be evaluated in terms of the total population present. On 16 November 2019 there was a total of 2,909 birds counted on our annual survey between kilometres 10 and 13 – an area that encompasses 5 of the 7 overhead lines. This included 2,800 BBG – mainly at the “Railway” colony. A similar count on 31 January 2020 gave 114 for the same area – many of these attracted by the easy fishing where the river was drying out.

Conclusions and Recommendations

Quite a large number of birds are being killed by the overhead lines with black-billed gulls being the most frequent victims.
No black-fronted terns were found, these patrol the river more than other species, but usually at lower speeds and below the level of the wires.
No dead wrybill were found. We only have about 8 pairs nesting along the Ashley, if any were to be lost to wires, this would be serious.
Next nesting season we should regularly look for birds under the lines – at least fortnightly. Some dead birds will no doubt get washed away by the river.
We shouldn’t encourage birds to nest close to lines by clearing weeds off islands near them. Before the “Railway” colony was formed, the gulls had started nesting very close to the sets of pylons upstream from Cones Road – this could perhaps have led to many deaths.
It is perhaps possible for the power companies to make the lines more visible; this could be explored when we have more information.

Grant Davey