Ashley Rakahuri River flood 30 May 2021
Left: 4.00pm 29 May. Water flow 4 cumecs.
Right: 4.00pm 30 May. Water flow 966 cumecs.
Photos: Nick Ledgard
Photos – Grant Davey
Left: 4.00pm 29 May. Water flow 4 cumecs.
Right: 4.00pm 30 May. Water flow 966 cumecs.
Photos: Nick Ledgard
Photos – Grant Davey
The main gauge of our success in looking after the indigenous birds on the river comes from our annual surveys of species numbers. This season, the survey took place on November 21, and is well reported in Grant Davey’s report (2020 Ashley-Rakahuri Annual Bird Survey). The total of wrybill, banded dotterels (BD), black-fronted terns (BFT), pied stilts (PS) and S. Is pied oystercatchers (SIPO) was 376 compared with 1004 last year and 461 in 2018. This was the third equal worst year on record (along with 2002) for these species – with the worst year being 2001 (285 birds). Before thinking ‘all is lost – we’ve failed’, consider this. Numbers plummeted after 2014 due to lack of large floods and a major expansion of invasive weeds. The 1-in-10 year flood of July 2017 brought the weed situation back to above the 2014 level and we thought the high 2020 survey figures indicated a great recovery. However, we now know that the exceptional bird numbers of that year were without doubt strongly influenced by floods in the Waimakariri forcing birds to move elsewhere. Right now the weeds are again advancing vigorously, so until we win that battle (see ‘Loss of habitat’ below) the bird numbers are likely to remain in the recovery phase. On the positive side, black-billed gull (BBG) Sept 21 survey numbers were 1820 (this species is not included in the above figures as a single colony can distort all-species comparisons), the second highest on record, and at the Smarts site BBG numbers had risen to 2846 a month later. Until relatively recently we had a BBG colony about every second year, but since 2016 a reasonable local colony has been an annual feature. At the time of writing, BBG numbers at the Smarts site (around 4ha) are 1780, of which around 1280 are flying juveniles. This would be one of our best ever BBG fledging results. The island site was cleared of weeds by a Taggart Earthmoving shingle extraction operation over the 2020 winter, and in addition to the large BBG colony, has attracted breeding BFTs, BDs, PSs, SIPOs and a single wrybill pair. As such, the site represents a vision of what bird life on the river can be, and this could certainly be improved further, plus hopefully replicated elsewhere (see below). At least 8 wrybill pairs took up territories over the season, which is the same as 2 years ago, and only a couple less than last season. Most of these hatched and fledged chicks. The species which remains of most concern is the BFT. Survey numbers were the fourth lowest on record, and their breeding success has once again been poor. Small colonies established to the nest/egg stage at 4 locations, but only the one at Smarts progressed to hatching chicks. Our monitoring of the Smarts colony this season has been mainly undertaken by Grant Davey, who regularly checks nests and traps in addition to aerial counts using our drone. The Group is extremely fortunate to have access to Grant’s data gathering and processing skills. I doubt if any other similar conservation entity in the country collects and publically presents such detailed results with such accuracy, clarity and promptness. For some weeks, Grant was greatly assisted by an ECan student intern, Matt Kim, who enjoyed spending hours observing the birds from our hide on the north bank of the river.
This remains our biggest challenge, and influences bird populations the most. The major concern is the rapid invasion of weeds – mainly lupins, gorse, broom, blackberry and willow, plus a range of grasses and other herbaceous species. The Smarts site, where bird breeding has been good, is a good example of this problem. It was virtually clear of weeds in September, but is now well covered in a new crop of seedlings. Weed invasion not only ruins bird breeding sites, but also smothers important shallow water/shingle margins where most feeding occurs. Nothing other than artificial clearing can be guaranteed to change this, as we cannot depend on natural floods. Last winter we cleared over 40 ha, mainly with a custom-built tractor-mounted undercutter. This coming winter we must do more of the same at selected sites which birds favour for breeding and feeding. Loss of open braided river habitat has also occurred as the berm zone (there to protect the stopbank) has expanded out into the open fairway – where birds feed and breed. As clearly stated in our 2019-20 annual report, over 50% of the fairway has been lost since 1942, and it continues to shrink to the present day. Excessive shingle extraction does not help to retain braids as it causes deepening and channelling of flow pathways. Discussions are underway with river engineers as to how this past management can be amended to enhance the ‘natural’ braided river character and extent of the Ashley-Rakahuri river. All this is part of a long-term planning process funded by ECan, and promised for consultation in the near future.
This is by far our major commitment in terms of personnel involved and operational hours – and continues all year round, both alongside the river and around the estuary. There is a total of just under 400 traps out there, serviced at least monthly by 25 volunteer trappers. Since July 1, 2020, trap-catch figures alongside the river read 10 cats, 63 hedgehogs, 21 weasels, 8 stoats, 1 ferret, 8 rats, 18 ship rats and 25 Norway rats. Whilst at the estuary – 2 cats, 3 hedgehogs, 15 weasels, 17 stoats, 0 ferrets, 10 ship rats and 13 Norway rats. Last season, our large BBG colony at the Railway site suffered major predation by rats and harrier hawks. This year, only 2 Norway rats and a mouse have been trapped on Smarts island (compared to about 15 rats and a stoat last year), and raids by harrier hawks appear to have been minimal. The latter could well be due to scarecrows erected close to the colony. On December 11, a trappers BBQ was hosted at the DOC offices, attracting over 30 participants.
The main way to reduce this is by making sure the public are well informed – via media articles, presentations and talks, displays, and our website and Facebook page. We now have a Promotions / Communications strategy, drawn up by professional advocacy member, Steve Attwood, and implementing that is a newly appointed Promotions Officer, Joan Miles. Our awareness efforts must be working, as compared to the past, this season has seen far fewer people and vehicle intrusions out onto the riverbed.
Apart from talking to groups, making presentations and manning displays, we accompany visitors to see what is actually happening on the river. Over the season, we have had visits by those who have gifted donations, ECan engineers and riverbed staff, the Waimakariri Zone committee, an Orari Rivercare Group rep, a TVNZ crew and our Mayor, Dan Gordon. All appear impressed by what they see, and are very supportive for the continuation of our efforts.
The Group is always closely following its accounts and budget situation – and generally our finances are in good shape. We are now mostly self-funded for our day-to-day existence, with monies coming from donations, our trap making and selling, and sponsorship via Karikaas Natural Dairy Products Ltd cheese sales. Funds for larger special projects, such as weed clearing, come from ECan.
Our 8-person Management Committee met on December 1, followed by a general meeting on December 3. The MC will meet next before the end of this month. Please mark Thursday, March 18 on your calendar for our next General meeting – starting at 7pm at the DOC offices on River Road.
As usual, many thanks to all our volunteers for the time taken to support our cause.
Title image: prior to the bird breeding season, commercial shingle extraction in the Ashley-Rakahuri river has cleared away weeds, and started to dig the channel which will create an island where the tractor is working. The tractor-mounted undercutter is making the site more attractive for bird breeding by roughing up the shingle surface.
Ashley-Rakahuri Riverbed Group members, Grant Davey and I, have just returned from the local riverbed, where the breeding season for indigenous species such as the ngutupare wrybill and pohowaru banded dotterel has been underway for about a month. We visited a site where much effort has gone into creating a desirable habitat for bird breeding.
Over the winter, prior to the breeding season, a local company, Taggarts Earthmoving Ltd, had extracted shingle from this site. Before they left, they made sure all weeds were removed, as it is well known that most braided river birds must have clean, weed-free shingle on which to nest. And over recent years there has not been the cleansing floods of sufficient size to clear away the increasingly invasive lupins, broom, gorse and blackberry. To complement this removal of the densest weeds, the Group has helped to develop a tractor-mounted undercutter to clear weeds from selected stretches of the river. Not only does the machine uproot weeds, but it creates the loose, coarse shingle surface most favoured by the birds. Our studies have shown that compacted or sandy surfaces are not so attractive to them.
Last August, we used the machine to clear almost 40ha of riverbed. Plus we got Taggarts to channel water across the tail end of their extraction site in order to create an island, which predators would find more difficult to access. However, as the old proverb says ‘one can take a horse to water, but one cannot force it to drink’. It is the same with the birds, one can create what one considers to be desirable nesting sites, but there is no guarantee that they will use them. Past experience has endorsed that.
But, this morning we observed the hoped-for and long-awaited results of our habitat creation endeavours. This is the reason why I sit here in front of my keyboard at home with a wider smile than usual.
As we waded across to the island earlier today, we noticed a movement amongst the stones. It was a female wrybill scuttling away through the stones, the give-away that there must be a nest nearby. So we retreated a short distance, and sure enough she soon came scuttling back and quickly settled down some 40m away. We waited a couple of minutes, taking careful note of the rock shapes and shades adjacent to where she was sitting. We did this, as seeing a wrybill settle on a nest is one thing – actually finding the nest is another. It is just a small-stone lined depression in the shingle and the eggs are the same colour as the grey-wacke rocks surrounding it. But find it we did, and while the adult bird gave us a broken-wing ‘distraction display’ just a few meters from us, Grant used his field tablet to photograph and GPS the nest location.
As we backed off, she quickly returned to shuffle down onto her eggs, appearing so relaxed that Grant crawled forward to take a few close-ups with his point-and-shoot camera. Within barely 10 minutes of first seeing the bird we were happily on our way back to the wagon for the drive home.
First of all, apologies for the lack of updates this year. In fact, there have been none, as the last was in December, 2019.
The last season was a good one for bird numbers, as nearly all species were present in record numbers. Breeding results were variable. Up to 10 wrybill pairs nested, raising 8 chicks, and for the first time since 2000 there were two black-billed gull (BBG) colonies containing over 2000 nests. There was also a record number of breeding black-fronted terns (BFT – 111 nests). But fledging results from both species was lower than the long-term average. All the details are in the 2019-20 annual report – due out before the end of this month. The start of this new season has seen the normal variable beginning. All the species are present, although so far only 2 wrybill pairs. The nests of both have been found, but one set of eggs has rather mysteriously disappeared, and the other is in a very vulnerable site. Good numbers of BFT and BBG have been seen, but they have yet to settle on nesting sites. Nests of banded dotterels and oystercatchers have been found, while pied stilts are again in good numbers. But it is still early in the season, so much will change. Once things have settled, we will arrange twilight visits to see the most accessible birds.
This is by far our major commitment and continues all year round, both alongside the river and around the estuary. There is a total of just under 400 traps out there, serviced at least monthly by 25 volunteer trappers. Rats remain the most common catch, followed by hedgehogs, weasels, stoats and feral cats – with numbers of the last mentioned being greater over winter. For the first time we have been deploying bait stations to try to reduce rats before the breeding season starts, as they were a major issue at the big colonies last season. As were harrier hawks, which we will try to deter using scarecrows. Another source of adult bird losses last season was power line strikes. This season we will seek volunteers to check under lines, so that we have the figures to support an approach to power transmission companies.
Weed invasion is arguably our major ‘new’ challenge. Between 2014 and early 2017 there was a significant decline in bird numbers caused by weed invasion and the loss of clear gravel breeding areas, before large floods over the 2017 winter increased clean shingle areas from around 30ha to over 250ha. However, these clear areas are now being reinvaded. As we cannot rely on good floods, around 35 ha was cleared in August by a locally developed tractor-mounted undercutter developed by Cresslands Contracting on Tulls Road. An Iranian PhD student, Sanaz Safavian, continues her studies of weed invasion successions on the riverbed at the Tulls site. Over recent times, the Group has become concerned about management leading to an ever-widening berm zone, which limits ‘room for the river to move’ and leads to loss of the ‘normal’ braided riverbed habitat essential for the long-term survival of riverbed birds. This matter is currently being discussed with ECan.
The main way to reduce this is by making sure the public are well informed. We do this by all sorts of means, and the annual report’s activity list contains almost 50 entries – mainly articles, interviews, presentations, displays, our website, Facebook page and video. In order to improve awareness further, at the next meeting (see below) we will be proposing the acceptance of a Promotions / Communications strategy, drawn up by professional advocacy member, Steve Attwood. More directly, we annually assist ECan to block off the major vehicle access-ways for the period between September and February . This was completed during August, with signs strategically placed explaining why. Talking signs, a professionally designed interpretation panel will soon appear at the Cones road bridge picnic area.
The Group’s finances are in good shape. We are now mostly self-funded for our day-to-day existence, with finances coming from a trap making and selling project (197 traps made and 116 sold in 2019-20), donations and sponsorship via Karikaas Natural Dairy Products Ltd cheese sales. Grants for larger special projects, such as the recent 35ha of weed clearing, come from ECan.
The COVID situation has allowed us only one general meeting this year – although our 8-person Management Committee has met on five occasions. So, please mark Thursday, October 8 on your calendar for our AGM, followed by a General Meeting. This starts at 7.30pm at the DOC offices on River Road.
As usual, many thanks to all our volunteers for the time taken to support our cause.
– Nick Ledgard, Chairperson
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.
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.
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:
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.
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.
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.
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.
Top image: remains of a DOC200 trap in the background and a Timms in the foreground.
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.
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.
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.
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.
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.
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
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.
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.
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
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.
Chair, Ashley-Rakahuri Rivercare Group Inc