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August 5 2020

Weed Removal Report

Background

Shorebirds breeding on braided rivers require clear shingle on which to nest. Over recent years the incidence of woody weeds has increased significantly on the Ashley-Rakahuri (AR) river. It is estimated that the area of clear shingle in the core bird breeding stretch of the river (21km between the Okuku river junction and the SH1 bridge) dropped from around 200 ha in 2014 to about 30 ha by January 2017. Subsequent major floods in 2017 increased this area to around 250ha, but maintenance of cleared areas will forever be a major challenge. To this end, a pilot trial using a bulldozer and rippers was carried out in July 2018. Its aim was to simulate a riverbed ripping technique which has been used for maintaining open bird breeding habitat within braided rivers in Hawkes Bay. Last year (2019) a customised ripper mounted behind a farm tractor was used. Reports on both the 2018 and 2019 work were written for ECan and DOC.

This report covers continued weed removal using the tractor-mounted machine in July, 2020. ARRG is most grateful for this weed clearance work being funded by ECan.

The full report is available here.

June 11 2020

Aspects of the Ashley Weed Problem

ashleyriver black billed gulls, black-billed gulls, black-fronted tern, management, research, weeds, wrybill

It is well established that birds that breed on braided rivers require bare gravel for their nests, and for many years members of the ARRG have understood that weeds pose a major threat to birds nesting on the Ashley. Exactly when weeds became a threat on the river is uncertain, but from the memories of various people, the fairway was essentially weed-free in the 1970s. Historic air photos have recently been obtained and will help in clarifying this. Efforts to clear weeds have been made since at least 2004 – these are documented in the full report.

Unfortunately, this has met with only mixed success and for some time weed pulling was done as a team building exercise rather than with real hopes of creating significant nesting habitat. Some years little or no weed clearing was done because floods had created plenty of bare gravel.

In early 2017 work was done that appeared to show that areas of past gravel extraction were preferred by nesting birds – however this needs to be revisited in more detail. Also, at this time areas of bare gravel were measured from air photos and satellite imagery for the length of the river, there appeared to be a strong correlation between bird numbers in the annual (November) surveys and bare gravel area. This work has led to further efforts to clear weeds. The outcome of that and the relationship between weeds and bird nesting success plus the future prospects are now available in this report.

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

February 11 2020

Fire and trapping update

ashleyriver black billed gulls, black-billed gulls, black-fronted tern, Trapping, weeds fire

Top image: remains of a DOC200 trap in the background and a Timms in the foreground.

River Traps

Early in February, there were two fires on the northern berm of the Ashley. The upstream one has incinerated 2 traps on Line M, all 13 traps on Line D, 10 of 13 on Line C and 7 of 20 on Line B. In addition, about 7 bait stations were burnt. The downstream fire was in the area of Line L and it is suspected that several the 15 traps here will also have been destroyed. When firefighting and clean-up efforts have been completed, we can assess where to put new traps – these will have to be purchased and boxes made for the DOC mechanisms. As of the evening of 6 February, the fires were still being fought and the area may still be subject to a crime scene investigation.

The drop in catch between November and December 2019 proved to be a false dawn – with a large increase this month – total of 87 predators in January vs 40 in December. Trap numbers in these months were similar. Last month it was speculated that perhaps bait stations were influencing ship rat and weasel numbers, this now seems to have been premature– with big increases in catch for both species.

Norway rat numbers have remained about the same, but hedgehog numbers have gone from 14 to 37. Now that the river has dried up for a large part of its course, hedgehogs are being caught on what used to be islands in the middle of the fairway. Three were caught on Line 192 after the river had dried out. These traps are around the large “Railway” gull and tern colony downstream of the railway bridge. The traps from the Toppings gull colony (Line 193 – where only 1 Norway rat was caught, after the birds had left) were shifted to a permanently vegetated island (now with dry channels around it) downstream from the Railway colony. Here they immediately caught 2 hedgehogs.

After the black-billed gull fledglings left the Railway colony it was possible to gauge the full extent of damage done by land predators. Despite our installation of temporary traps around this colony, it appears that about 110 gull chicks (from about 900 nests) were killed and eaten by ground predators – around 100 of these are suspected to be by Norway rats. Our traps at probable den/nest sites in willow near the edge of the water were quite successful in catching rats, but it appears that other rats walked right past our traps which were closer to the colony. Nothing was caught in these traps – along a line of lupins. Fresh gull chick was obviously much more appetising than cat biscuits and peanut butter in a run-through trap.

The rats have eaten their prey very close to where it was caught – within the colony perimeter. In places there are piles of remnant carcasses. They leave bones and wings, gnawing away the meat and sometimes just making a hole in the bird’s abdomen.

Young gull gnawed by rats

Young gull partially eaten by rats

Traps, colony edge (yellow lines) and some land predator kill (pink symbols with numbers)

Only one other predator was caught on the Railway colony island whilst the birds were in residence. This was a stoat – it appears to have carried several young birds about 250m away from the colony and eaten them under willow. Much less was left of these birds – only parts of wings.

More evidence is of course needed as to the nature of the predators. We only caught Norway rats and 1 stoat during the period the birds were there, but it is possible that other predators were active. Next season we should have more trail cameras available. We have had 2 on the island this year, one got stolen and the other is still in place.

Next season bait stations will probably have to be used close to colonies and weeds close to the colony areas will need to be pulled.

Harriers were even more prolific killers than the rats – about 117 gull chick remnants can be attributed to them. They catch young gulls either from the ground or in the air and take them to the riverbanks to eat. At the end of December only about 20 gulls appeared to have been killed by harriers. This dramatically increased once the young gulls left the colony area and had fewer adults to protect them. Last year harriers were almost always entirely eating their prey – leaving just piles of feathers. This year many young gulls were only partly eaten. It appears that one or more harriers were catching more than they could eat. Harriers are rather like black-backed gulls in that their numbers are unnaturally high. Next year we might have to consider using scarecrows to protect nesting colonies.

The remains of 91 chicks that probably died naturally were found within the Railway colony area. At this colony it wasn’t possible to get a count of birds that successfully fledged.

At the Toppings colony no predators were caught during the time the gulls were in residence and no evidence of ground predation was found. Harriers here appear to have killed and eaten only 3 gull chicks.

The damage that harriers may have done to tern eggs and chicks is not known. But Norway rats are strongly suspected of wiping out many nests and perhaps killing chicks.

The graph below shows that Lines 192, F and M caught the most predators in January.

Catch per line in January 2020

We report catch per hundred trap night figures at six-month intervals – from February to July and from August to January (approximately the nesting season). This figure, from 1 August 2019 to 31 January 2020 was 0.48. This is quite similar to that from recent seasons.

Estuary Traps

Catch continued to increase with a total of 26 compared to 22 in December. There were a few more predators caught in January 2019 than in January 2018 but there were two extra lines – I and J were put in during late January 2019.

Predators caught per month, July 2018 to January 2020

Rats were yet again the main catch – with Ship rats outnumbering Norway rats. The number of hedgehogs caught in January (4) was the largest for a month since we started trapping. In

the last two months we have caught 6 hedgehogs compared with a total of 9 in the preceding 17 months. The area has had an unusually low hedgehog catch compared with further up the river and the Tuhaitara area, hopefully this isn’t the start of a hedgehog comeback. Stoats still make up a greater proportion of the catch than is the case further up the river.

This season pied stilts, banded dotterels and black-fronted terns nested on a large gravel area just above where the river enters the estuary – this is between lines C and D. There were also banded dotterel nests further up the river close to SH1 and at least one black-fronted dotterel also nested along here. No attempt was made to follow the success of this nesting or to try to ascertain whether land or airborne predators were active. The biggest threat to the birds was probably human disturbance, especially during the whitebait season when there were a lot of people, vehicles and dogs along this section of the river. Black-backed gulls could also be a major problem. Some dotterels seem to have successfully nested along the beach and other species such as oyster-catchers were nesting elsewhere. Perhaps the estuary trapping group could do some nest monitoring next season. Failure of dotterel nesting at Kaikoura has been a major issue, it would be useful if we could find out what the situation is in our area.

Fledgling wrybills, black-billed gulls and black-fronted terns tend to congregate in the estuary after leaving the river. These would probably also be threatened by predators. This year several young terns and black-billed gulls were there. On 28 January about 125 black-billed gull fledglings, with some adults, were seen between the eastern ends of Line C and Line B. These were almost certainly from the Toppings colony.

Banded dotterel chick on the beach – October 2019

Lines D, F and G had the largest catch in January.

For the 6 month period between 1 August 2019 and 31 January 2020 the catch per 100 trap nights was 0.36.

Grant Davey, 6/2/20

Catch per line, January 2020

February 3 2020

Drying river rewards birds

ashleyriver black-fronted tern drought, drying, spoonbill

As the birds which breed on the Ashley-Rakahuri river come to the end of their breeding season, stretches of the river are often in the process of drying up. That means their food, small fish and aquatic invertebrates, are vanishing into ever-shrinking pools, where they are easily captured by the birds. “Numbers of hovering terns and gulls, plus busy dotterels, stilts and oystercatchers can currently be seen at these water remnants,” says Ashley-Rakahuri Rivercare Group member, Grant Davey. “When I was down there last week, good numbers of shags and white-faced herons were also present – and even a few of the much rarer spoonbills.”

[image above: Three black-fronted terns hovering over a riverbed remnant pool where small fish and aquatic invertebrates are being concentrated. (Photo – Grant Davey)

A spoonbill joins a pied stilt and a couple of juvenile terns around a remnant pool in the drying Ashley-Rakahuri river (Photo – Grant Davey)

“This drying of the lower reaches of the river is not unusual,” says Ashley- Rakahuri Rivercare Group chairman, Nick Ledgard. “The timing varies from year to year, and with declining rainfalls in the upper catchment, could well be happening more often – but it is not a new phenomenon, which some people claim.”

Once the water disappears, so do the birds, with most of them heading for the estuary and the coast and often further north for the coldest winter months. Wrybill fly up to feeding grounds in the northern N. Island, particularly the mudflats of the Manukau harbour and the Firth of Thames. They are not expected back until the spring, when they are first seen down around the estuary before flying up the riverbed to their traditional breeding sites.

Fresh-water flounder are not often seen far up the Ashley-Rakahuri river. This one was in a drying up riverbed pool some 8 km away from the coast. (Photo – Nick Ledgard)

January 21 2020

Survey of the lower part of the Okuku River: November 2019

ashleyriver annual survey, black billed gulls, black-billed gulls, black-fronted tern

The Okuku is an NW to SE running tributary of the Ashley, joining the latter about 22km inland from the coast.

An attempt was made, with Jean Jack of Environment Canterbury, to survey the Grey junction to the junction with the Ashley on 20/10/19, but water levels were too high. On 11/11/19 flow at Fox Creek was only 1.5 cumecs, making river crossings easy.

The survey was done from just below the Grey River bridge on Loburn Whiterock Road to the mouth of the Okuku. Thus the first interval, 8-9 on the below table, was a little longer than a kilometre.

Observations on the survey:

The river has a fairway of up to about 200m width usually with 1 – 2 active channels. A fairly recent sizeable flood seems to have cleared most of the fairway weeds, but some are regrowing.
There were 4 gravel operations seen, 2 large and 2 small. No extraction was currently being done at any of these.
The gravel extraction areas are a definite locus for bird activity and breeding – particularly banded dotterel and pied stilts. Shallow ponds were present at all sites, stilts were seen feeding in these. Extraction areas, shown in yellow in the below map, are approximate only.
There wasn’t evidence of much 4wd activity along most of the riverbed, except for downstream of the Birch Hill bridge. This seems to be a major 4wd access to the Ashley River.
A group of horseriders were seen along the berm of the Ashley just downstream from the Okuku junction, they seemed to be heading out onto a bare gravel island where stilts could be seen.

About 20 cattle were roaming along the eastern berm, and crossing the river to some extent, west of Harpers Road.

Shallow ponds from gravel extraction, Grey River. The title image are shallow ponds, gravel extraction area west of Yaxleys Road.

Bird observations (numbers tabulated below)

Banded dotterel: only seen at and near the gravel extraction area in the Grey River. There were 4 pairs here with 1 almost fledgling chick seen. This is a similar number to that seen on 20 October, the fact that the birds remained there perhaps shows that breeding was successful.

Pied stilt: these were seen at or near all the gravel extraction areas. A total of 20 were seen, with 8 each at the two larger operation areas. One nest was found close to the old extraction area in the Grey and elsewhere the birds’ behaviour indicated nesting.

Black-fronted tern: a total of 12 were seen hawking along the river, sitings near the extraction areas were probably coincidental. The most were seen, 4, just above the Ashley confluence.

SIPO: one was seen at the extraction area north of the Birch Hill Road bridge. This almost certainly had a nest or chicks.

Other: these consisted of typical river birds, including white-faced herons, mallard ducks, Canada geese and little shags. They were distributed along most of the river.

January 21 2020

Lees Valley – Okuku and Ashley-Rakahuri Rivers: 2019 Breeding Season

ashleyriver annual survey, black billed gulls, black-billed gulls, black-fronted tern

Introduction

The Okuku is a NW to SE running tributary of the Ashley, joining the latter about 22km inland from the coast. It rises in the Pancake Range north of Lees Valley, runs through this valley and enters the Okuku Gorge. The section through the valley is about 3km long, here the river is relatively wide. The gorge section is about 10km long and is quite narrow. From the south end of the gorge the river runs for about 15km to the Ashley confluence.

The Ashley rises in the Puketeraki and Pancake Ranges and upper branches of it run for a considerably greater distance through the flat Lees Valley.

On October 20 2019 Jean Jack of Environment Canterbury surveyed river birds on short sections of the Ashley and Okuku Rivers in Lees Valley in response to proposed gravel extraction. The 700m Ashley section was just downstream from a bridge some 10km northeast of the Ashley Gorge. In this area black-fronted terns (BFT), banded dotterels (BD) and pied oystercatchers (SIPO) were displaying breeding behaviour – but no nests were found. Three kilometres of the Okuku River was surveyed either side of the Lees Valley Road crossing. Birds found here included BD, BFT, southern black-backed gull (SBBG), SIPO, black-billed gull (BBG) and pied stilt (PS) – most displaying breeding behaviour. A colony of 25 BFT was identified, although nests were not found. A black-billed gull colony was found just below the Lees Valley Road river crossing, at that stage only 8 birds were present.

BRaid activities

The evidence of braided river birds breeding in the Lees Valley was thought by BRaid to be worthy of further monitoring. On 21/11/19 the Ashley and Okuku sites were visited by Grant Davey and Howard Esler. Further visits were made to the Okuku site on 19/12/19 and 14/1/20 by Grant Davey and Nick Ledgard.

Ashley River

Birds were counted along 1.4km of the riverbed downstream from the upper Lees Valley bridge. These included 8 BDO, 7 BFT, 6 SIPO and 4 PS – constituting a large population of birds in such a short section of narrow riverbed. Several terns were resting on the ground, but their behaviour did not suggest the presence of eggs or chicks. They may perhaps have had nests but lost them to predators. Four juvenile BDO were seen, 1 in flight – they seem to have had a successful nesting season. SIPO behaviour suggested the presence of 3 nests and stilt behaviour suggested 2 nests.

The area traversed was within and just downstream from where gravel has been extracted in recent times. Gravel extractors have probably created favourable nesting habitat.

Okuku River

When visited on 21 November the 2.5km of riverbed traversed from just below the road crossing to 2.5km above also had a very high concentration of braided river birds for such a small river. These are illustrated and tabulated below:

The BDOs were mainly in pairs and appeared to have finished nesting, however only 1 flying juvenile was seen. Most of the SBBG were resting on the ground close to tern colonies. Stilts were breeding in the area and 1 nest was found. The SIPO did not display obvious breeding behaviour.

Fourteen BFT nests were found – 2 were empty, 1 had a dead chick and a live chick in it, 1 had a single egg, the remainder had 2 eggs. No concerted effort was made to find nests, but they were quite easily located – those found would likely have been more than half the total present. Three clusters of nests were found – about 0.6, 1.4 and 1.5km upstream from the road crossing with 3, 9 and 2 nests respectively. The nests were on weed-free islands up to about 15m in width.

Black-fronted tern colony, looking downstream.

The previously observed BBG colony had expanded to 292 gulls – counted from a drone image. Chicks had yet to hatch. This colony was in coarse gravel on an island (see the image at the top of this post taken 29 November, looking toward Okuku Gorge).

The visit on 19 December was specifically made to monitor the tern and gull colonies. On this date there was no activity at the lower and upper BFT colonies, but at least 6 juvenile terns were seen at the middle and largest colony. Three were flying, another appeared to have a broken wing and 1 was yet to reach fledgling stage. The chicks were observed from the riverbank to minimize disturbance and it seemed likely there could be more than were counted.

On 19 December the wind was too strong to fly the drone, but the BBG could be counted quite accurately (198) off photographs taken from the adjacent high bank. The reduction in adult numbers since 21 November was in line with experience from colonies on the Ashley River (this happens while nest and chick numbers remain largely the same – non-breeding adults leave the colony and breeding adults spend more time away foraging). Most eggs appeared to have hatched with chicks ranging from recently hatched to perhaps about 2 weeks old.

Pair of BBG chicks being fed, other gulls still on nests, 19 December 2019.

Discussion

In November braided river bird numbers were high on the short sections of the Ashley and Okuku Rivers that were traversed by ECan and BRaid. On the Ashley these numbers were likely boosted by the positive influence of gravel extraction. The following points are specific to the Okuku River:

The black-billed gull colony appears to have been successful. Chicks were hatched and from the lack of predation evidence and low number of dead chicks in the colony area, many were likely fledged.

The black-fronted terns appear to have had some fledgling success, probably higher than that of those on the lower Ashley in 2019 – 2020.

Ground predator numbers in the area seem low – no sign of predation was seen around the gull colony and the landowner/manager (Craig Thompson) reports having seen very few predators in his time on the property. Rabbits were common, this could perhaps lead to more predators in the future.
Black-backed gulls are plentiful in the area, much more so than along the Ashley River. However, there was no evidence seen of them being active predators of braided river birds. Harrier numbers also seemed high.
The area has notably few invasive weeds. The banks have mainly grass and matagouri with in places a number of native species present. The most obvious weed is Vipers Bugloss.
Larks (pipit/skylark?) were abundant in the area.
The contribution to braided river bird nesting success of such small out of the way rivers is probably underestimated. It is planned to revisit the Lees Valley next nesting season and to survey the Okuku for some kilometres upstream from where it enters the gorge. There could have been other nesting colonies upstream of those observed this year – the landowner mentioned that he may have seen more nesting terns higher up.

– Grant Davey

black fronted tern and chick ashley river

January 9 2020

Ashley River & Estuary trapping update

ashleyriver black billed gulls, black-fronted tern, management, Predators, trail cameras, Trapping, weeds

River Traps

The below graph shows a reduction of catch in December compared to November. This was due to fewer ship rats and weasels being caught. Perhaps our baiting programme is starting to work – with weasels being secondarily poisoned? Hedgehog, stoat ,and non-specified rat numbers increased a little. Unfortunately, the January catch, shown here to the 8th, is on track to easily exceed that of November, so the December reduction might not be significant. We have not caught a feral cat since October last year. Geoff has started cutting out the backs of Timms traps and replacing them with mesh; this hopefully will make these traps more successful.

The next graph shows that catch from the two colony lines – 191 and 192 – has declined from the previous month and is now comparable to that from the permanent riverside lines. (If something looks incorrect, please let me know). Unexpectedly Lines 193 and 194 (at a black-billed gull and black fronted tern colony and BFT colony respectively) still haven’t caught a single predator. Lines 191 and 192 are at a BFT colony and BFT & BBG colony respectively. The only predators caught out on the gravel adjacent to nests are still Norway rats, and these currently seem to be the main land-based predator danger to nesting birds – especially BFT and banded dotterel. There appears to have been zero BFT fledgling success from the Railway colony (about 50 nests), with more than half of the nests being predated before hatching, and chicks disappearing at an early age. There have been only 2 -3 fledgling BFTs seen at the Thomas/G9 colony. The G4 colony looks like being more successful – very likely because of lack of predators. The Toppings BFT colony was very small with only a few nests found. Some eggs hatched, but chicks haven’t been seen lately.

A few young gulls have perhaps also been caught by Norway rats at the Railway colony, evidenced by piles of feathers near the colony. The main predation here, though, has been by harriers. More than 20 piles of fledgling gull feathers (see below) have been found on the southern river bank so far. This could well increase to more than 50 as it will be some time before all the chicks can fly away. Nick has captured an image of a harrier carrying a gull on a trail camera. As with last year, the main danger to the gull chicks seems to be when fewer adults are around to protect them from harriers. This predation is of course a natural process.

Nick has captured an image of a harrier carrying a gull on a trail camera. As with last year, the main danger to the gull chicks seems to be when fewer adults are around to protect them from harriers. This predation is of course a natural process.

Harrier carrying young gull, with adults in pursuit – top left and shadows

The following map shows where the various types of rat have been caught since August last year, when we first started distinguishing the different species. Pie chart size represents the number of rats caught in a trap with the largest catch being 5 and the smallest 1. The colony lines 191 and 192 out in the gravel have caught by far the most Norway rats. However, 13 in total have been caught along the south bank, generally in traps very close to the river. Some of these traps have caught both Norway and Ship rats. By contrast only 2 Norway rats have been caught on the north bank, on Lines M and E. The Norway rat on Line E was very close to the colony. Perhaps the south bank is a source of Norway rats; we maybe should be increasing our baiting efforts there.

Estuary Traps

Catch in December continued to increase with a total of 22 predators compared to 17 in November. In December 2018 total catch was also 17, however Lines I and J were only installed in January 2019.

Rats were once again the main contributor but this month Ship rats outnumbered Norway rats. Lines A and B failed to catch a predator in December. A hedgehog was caught on Line G – the first since May 2019 and only the 10th caught since trapping began. No cats have been caught since August 2019.

The following map (the smallest pie chart represents 1 rat per trap, the largest 3) shows that Norway rats have essentially been caught in the period August 2019 to 8 January 2020 only along both banks of the river above where the river meets the estuary. It appears that the river margin is more of a habitat for them than the estuary margin. Ship rat distribution was more widespread. More bait stations are needed, especially on Lines I and J.

– Grant Davey, 09 January, 2020

December 13 2019

Ashley-Rakahuri Rivercare Group update

ashleyriver annual survey, black billed gulls, management, Predators, Trapping, weeds, wrybill

Down on the river – bird numbers. Without doubt, the highlight of the last few weeks has been our annual bird survey on November 16. The Group’s mission is to improve the lot of the native birds which annually return to breed on our river, and our once-a-year surveys are the only chance to find out if we are achieving this goal. So, it was most rewarding to see 29 volunteers gathered on a fine (if windy) Saturday morning to get their survey instructions. The river flow was such that crossings were challenging, but certainly do-able, so that everyone completed their stretch and were off the river by midday. Needless to say, the survey sheets were quickly gathered and analysed, revealing that numbers for all species were the highest since we began in 2000 (see bar graph below). We saw 27 wrybill, 6 more than ever before. Thanks to there being two colonies this season, numbers of black-billed gulls (BBGs) were many-fold higher than before (over 4000). However, they are not included in the graph, as the presence or absence of a single colony, can have an over-riding influence when comparing total bird numbers from one year to the next. We reckon that the increase is mostly due to greater areas of clean shingle (less weed presence) since when bird numbers started to decline after 2014. Plus the fact that other adjacent alpine-fed rivers (such as the Waimakariri) were in full flood, forcing birds which usually occupy them to look elsewhere. This is almost certainly the case for black-billed gulls. A new species for a survey was the black-fronted dotterel (4 of them, and almost certainly breeding); a species which has been steadily increasing its range south over recent years.

Down on the river – breeding success. Determining bird populations is much easier than recording breeding success, particularly if one is trying to determine the influencing forces. This requires constant monitoring of adults and chicks, the latter often being very hard to detect. We only monitor details for wrybills, black-fronted terns (BFTs) and black-billed gulls (BBGs). At least 8 wrybill pairs took up territories, with nests found in 5. Fledged chicks have been seen in 3 of these. Four BFT colonies were located (involving possibly 80 pairs), but no chicks have yet fledged. As mentioned above, the biggest breeding increase has been with BBGs, with two large colonies (Railway and Toppings) which have numbered well over 4000 birds. The number of nests is hard to determine accurately until the sites are vacated, but it would be 1500+. Chicks are in the process of hatching, and some are just reaching the age at which they gather together in creches. It appears that some BBGs are still just arriving (late refugees from other flooded rivers?), so the fledging period may be more drawn out than usual. Good numbers of breeding pairs of other species (pied stilts, banded dotterels and S. Is pied oystercatchers) are also present on the river.

Trapping. Grant Davey sends our 27 trappers excellent monthly summaries concerning predator trapping results. Even though individual trappers may be currently experiencing a low catch rate, the overall figures for this year show that we are making an impact. Since February 1 this year, we have caught 411 predators alongside the riverbed – with rats and hedgehogs being No 1 (112 and 111), followed by weasels (77), feral cats (37) and stoats (24). Out around the estuary, the catch figures are quite different. Since we started in late June last year 344 predators were caught – with rats being at the top (168), followed by weasels (91), stoats (34), feral cats (14), hedgehogs (8) and ferrets (7). In addition to this trapping effort extending over 21 km, we have been doing more intense grid trapping around the BBG and BFT colonies – using 53 specially made, lightweight and cheaper run-through corflute tunnels, housing DOC 150 traps. The main target is Norway rats which appear to be escaping attention by living in mid-river debris piles – as they are not being caught in the berm zone where virtually all of our other traps are located. Rats can be devastating on BFTs at the egg-nest stage, and were probably responsible for the loss of 20 BFT nests at the Railway site before the offenders were trapped. Interestingly, BBGs nesting right alongside were not troubled, almost certainly because rats will not take on aggressive gulls nesting in close proximity to each other.

Weeds. As mentioned in the October Update, before the season started we cleared weeds from a number of hectares using a specially created tractor-mounted ‘undercutter/ripper’. The Railway BBG/BFT colony is occupying one of those sites. And as indicated above, the record numbers of birds counted this season, could well be responding to greater areas of clear, weed-free shingle than there was from 2014-2017. However, the threat of weed invasion is as great as ever – well indicated by the dominant lupins, which are currently flowering and colouring much of the riverbed yellow. Not so obvious are other weeds such as broom, gorse and blackberry and the equally frequent younger lupins which have yet to flower. Unless a major flood occurs before next season, or we step up our weed control efforts, then bird numbers could well decline again as the clear shingle areas become invaded. A recent inspection of the smaller foothills-fed rivers in S. Canterbury (such as the Opihi and Orari) amply reinforces this ‘beware of weeds’ message.

Human disturbance. After predators and weed invasion, the biggest threat to the future of the birds is disturbance by humans. Our awareness efforts, coupled with good signage and the physical blocking of 4WD access ways during the breeding season, means that disturbance by people and their machines is way less than it used to be. To be sure, there will always be the small percentage of people who wreck signs and go out of their way to get onto the riverbed, but there is little that we can do about them. At many of our meetings, there is vigorous discussion as to how best to increase public awareness, as it is often difficult to determine the relative cost-benefit of expenditure in this area. To this end, the Group recently formed a promotions sub-committee to work on a strategy which allows us to better plan our public awareness efforts.

The future. There is little doubt that the Group’s many years of management, primarily aimed at controlling predators, reducing human disturbance and removing weeds, has contributed to the present buoyant situation for the birds on our local river. It is equally accurate to say that we will have to continue this effort to maintain a positive situation – probably even increase it relative to weed control. In this respect, we are fortunate that over the last couple of years ECan has prioritised a step-change in its indigenous biodiversity efforts, and agreed that braided rivers be identified as a priority area for increased attention. A commitment was made to produce nine braided river plans over 10 years to 2028, and the Ashley-Rakahuri river was chosen to be one the first cabs off the rank. We are having discussions as to the form this might take, but the result should be an improved ability to ensure a better future for our local braided river birds.

Many thanks to all our volunteers for the time taken to support our cause.

Nick Ledgard

Chair, Ashley-Rakahuri Rivercare Group Inc