May flooding
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
June 01
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
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.
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.
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.
Nick Ledgard
Chair, ARRG
Title image: Key braided river bird locations: 2018, 2019, and 2020.
A PDF of this report is available here
Introduction
The Ashley Rakahuri Rivercare Group (ARRG) has an unbroken 21-year history of annual bird counts – running 19km from the Okuku junction to State Highway One. For the last 3 years we have also included the 2km section from SH1 to the top of the estuary and have counted the birds in 1km stretches of the river. This counting method has now been standardized across Canterbury. The graphs (other than that for the black-billed gulls) and numbers in this report show data that excludes the lowermost 2km of the river.
On 21 November this year we had 22 active participants in 4 groups on the usual river reaches – starting at about 9am. In the early afternoon 2 surveyors did the 2km down to the estuary. There was a weak to moderate northwesterly wind, cool conditions, and river flow of about 8 cumecs at the Ashley gorge (Figure 1). There had been a small flood of 50 cumecs on 8 November, this was enough to wash away some black-fronted tern nests near Groyne 9 and near Cones Road bridge – but the birds would have had time to re-nest before the survey.
This year most participants had radios, although a few were faulty or had insufficient battery life. Radios improve communication considerably and should lead to less double counting.
For the past 3 years we have counted black-billed gulls in colonies using drone photographs – this year the day before the survey. This leads to considerably more accurate numbers, and almost inevitably higher ones than would have resulted from a land count.
Overall Numbers and Bird Locations
The 6 key braided river bird species that we are most concerned about are wrybill, banded dotterel (BD), black-fronted tern (BFT), southern pied oystercatcher (SIPO), pied stilt (PS) and black-billed gull (BBG). Numbers since 2000 of the former 5 species are plotted on Figure 2 and Figure 3 with BBG on Figure 4 – as the BBG numbers tend to overwhelm those of the other species when plotted on a graph.
Some observations:
Of note are –
Comments on Individual Species
Ten wrybill were counted this year, this is considerably fewer than the 27 last year and less than the average since 2000 of 13. One bird seen between kilometres 3 and 4 had not been previously monitored this year. Only one wrybill was seen east of Cones Road when there were 2 nests in this area (at Marchmont and Smarts) this year. The Marchmont birds have not been seen since the small flood of 8 November. This should not have affected the large chick that they were guarding, but maybe it has been predated.
Most of the wrybill were seen in kilometres 6 to 8. None were found in the vicinity of Groyne 1 where a pair were successfully raising a chick just before the survey – however a few days later one was seen in this area showing chick guarding behaviour.
Last season 9 pairs of wrybills were seen on territories, this year there had been 8 pairs seen. Many of the 27 wrybill seen in the 2019 survey are likely to have been displaced by floods from the Waimakariri, and did not nest on the Ashley.
The 133 BD counted this year was well down on the 323 last year and the average of 209. However, the northwest wind perhaps caused BD to be under-counted. Several times birds were seen up close, keeping low and not making noise when they would normally be expected to fly when approached. With this behaviour, and sometimes quite widely spaced surveyors, some birds would be missed. shows evidence for this undercounting – there was an unexpected drop in BD numbers eastward of Cones Road from the week before the annual survey when numbers of other species remained very much the same or slightly higher. Tightening up of survey procedures, leading to less double counting, could also cause numbers to drop. The way BD circle around out of their territories when disturbed makes them prone to double counting.
Several BD chicks were seen in the survey, but perhaps not as many as should be expected. Early in the season a number of BD nests were found and monitored, most of these were not successful. One was lost to a small fresh and one to a harrier – caught by trail camera.
BD were most common in the few kilometres downstream from the Okuku junction and near Cones Road.
The 65 counted this year was the fourth lowest on record, 2005 (26), 2004 (28) and 2001 (44) had the lowest numbers. In 2019 there were 296 counted. BFT numbers were the most reduced of the key species compared to 2019. Numbers do seem to have increased slightly eastward of Cones Road in the few days after the survey – with some more nests having been made.
This looks to be a very poor breeding season for BFT – although there is still time for some to nest. At the time of the survey nesting seemed to be taking place only in 4 locations – very close to the Cones Road bridge (only a handful of nests), on the Smarts island where Taggart cleared weeds (2 clusters of maybe 3 nests each) and probably a few nests immediately above the estuary. Prior to 8 November there had been a good colony off Groyne 9 – with around 20 nests mainly on an island that ARRG had cleared of weeds this year. Some of these nests were abandoned prior to the small flood of 8 November, some were washed away in the flood, and some were abandoned at this time despite not being flooded. The reason for the abandonment is not known – although there had been 4wd and motorbike activity through the colony despite signage. During the day the vehicles weren’t causing abandonment, but at night they could well have done. These birds have had time to renest in this area after the flood, but have not done so.
Figure 5 shows that eastward of Cones Road BFT numbers have dropped steeply since late September. The birds were here, but decided to nest elsewhere. Reasons for this are not understood, there appears to be enough bare gravel for them to nest – areas that ARRG has cleared and others – including a large naturally clear area near Groyne 4 where there was a big BFT colony in 2019. Perhaps the answer has to do with food supply. Birds have been captured on trail cameras bringing worms to nests, not the more usual whitebait.
On 18 November 1820 were counted from drone photos at or near the colony on Smarts island. – with just a few elsewhere along the river – mainly near the estuary. This is the second highest number on record – after 2019 when there were 4097. On 11 November there had been 2846 at the Smarts site, but numbers are following what now seems to be an established pattern – maximum numbers occurring around a week after inception of the colony, then many birds leave the area.
Nests have yet to be counted, but there are perhaps in excess of 1000.
Until relatively recently on the Ashley we have had a BBG colony about every second year, but since 2016 a reasonable local colony has been an annual feature. Figure 4 does not show the 2016 colony in a dairy farm paddock just southeast of the SH1 bridge.
This was the most abundant species on the river this year – although the total number at 141 was still less than the average of 163. This was the 10th worse year on record for PS.
Stilt numbers increased significantly in the lower half of the river since August – Figure 5. In the survey annual they were seen to be most abundant near the estuary, at Smarts, Tulls and near Groyne 2. None at all were seen in kilometres 1 to 3 downstream from the Okuku junction. Their behaviour in most places showed that they were nesting.
Twenty-seven SIPO were counted this year, down significantly from 2019, but essentially the same as the long-term average of 28. SIPO and PS are the least threatened of the braided river birds and nest in several other environments.
They were seen sporadically along the river. As with BD, they are early nesters and most of them probably had chicks. Two dead adult SIPO were seen off Groyne 9, they had perhaps been shot.
Fourteen SBBG were counted, this compares with the long-term survey average of 11. All but one of these were seen between kilometres 12 and 19. In the previous twelve one person counts of this area this year, the average seen was 4, so this years annual survey result does not represent an increase in SBBG. These birds are a major predator of braided river bird eggs and chicks on other rivers such as the Waimakariri and Waiau – where they nest in large colonies. They also nest at the Ashley estuary, but for reasons unknown, they are quite rare further up the river. In the last 15 years only 1 SBBG nest has been found in the Ashley riverbed.
Black-fronted Dotterel
Seven were seen between kilometres 13 and 17 (Marchmont to Toppings). This compares with a maximum of 5 seen in the same area in the weekly surveys. A further bird was seen east of SH1. Black-fronted dotterels have been increasing in abundance in the last few years (only 1 counted in 2019) and have been seen further upstream as time goes by. They are usually found in sandy or muddy backwaters which aren’t classic braided river habitats. For years they have been well known in the Waipara river and are quite common in the Opihi. These rivers are degraded and channelized braided rivers and increasing numbers in the Ashley may not be a good sign.
Spur-winged Plover
Twenty-one were counted in 2020, this compares to a long-term average of 41. This species is highly erratic in distribution, sometimes occurring in large flocks, sometimes with only a few individuals. The maximum seen in a survey since 2000 was 149.
Water Birds
Ducks, shags, Canada Geese, white-faced herons and paradise ducks are found along the river but are not specifically braided river birds. They actually prefer deeper water channels that run along the edges of the fairway close to trees – and thus are maybe an indication of the degradation of a braided river. In the Opihi, an extremely channelized and degraded river, the average ratio of braided river birds (wrybill, BD, BFT, PS and SIPO) to these river birds in the 4 years of surveys was 1.2. In the Ashley for the past 3 years this ratio has been 4.4, 6.5 and 3.4 respectively. The total of these birds counted this year was 111.
Figure 8 shows the distribution of these birds, with pie charts scaled the same as in the previous maps. Shags (predominantly little shags) and ducks were most abundant near the estuary and in the single channel river for a few kilometres upstream of it. Further upstream paradise ducks predominated. Early this year when the river was drying up, shags, herons and even royal spoonbills were quite abundant further up the river where they were fishing in drying sections of the river.
Other
Twenty-four harriers were counted this year, but it appears that some double counting has occurred as more than one person in each group was counting them – despite instructions for one person per group to do this. Numbers from previous years are unreliable as these birds are generally seen only in the distance. Harriers are a major predator of braided river bird chicks on this river, and perhaps also of eggs. One was captured by a trail camera raiding a BD nest this year.
One Caspian tern was seen east of SH1. No unusual birds, which have occasionally been seen in the past, such as white-winged black tern, were observed.
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.
Nick Ledgard
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
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.
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.
(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.
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 |
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.
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
Grant Davey