Gronant Little Tern Report 2020
The following article has been sent to us by Henry Cook
Nesting Little Tern by Miek Stecuik (under licence)
The following report details the 2020 breeding season for the little tern Sternula albifrons at Gronant, Denbighshire, North Wales. This is the 16th year that the colony has been managed by Denbighshire Countryside Service (DCS). Historically, this work has been carried out in conjunction with the North Wales Little Tern Group and volunteers, but this year the working relationship had to be altered due to the outbreak of COVID-19.
This season has been unprecedented in terms of challenges faced by both the terns and our staff. As of the 23rd March, systems were put in place in order to try and mitigate the COVID-19 outbreak worldwide. For our staff, this meant our usual working procedures had to be changed dramatically. Unfortunately, this meant we were unable to hire the usual three wardens and one engagement officer to manage the site. DCS staff were able to cover the usual warden duties with help from Denbighshire’s Biodiversity team and Keep Wales Tidy staff. The outbreak also meant that DCS staff were unable to carry out any work alongside volunteers, and had to stick to strict social distancing and sanitization guidelines where more than one person was present on site.
This year we did not install the visitor centre or hide, and under COVID-19 guidelines, were n unable to open the site to visitors. Visitors were instead asked to view the birds from outside the blue perimeter rope.
This year also held many challenges for the terns. Along with adverse weather events, the terns were subject to high predation pressure (See sections 3.8 and 4)
Figure 1: Key Season Events
Site Overview and Equipment
Where we usually have all of our staff, the NWLT group and volunteers helping to set up the protective boundaries and fencing, this year we only had a maximum of 3 members of staff working at any one time and at a safe distance. With this small team, we were able to get all of the fencing in place, covering prime areas of nesting habitat over a period of only a week and a half. On 31st March, the blue perimeter rope was installed, encompassing the site and preventing footfall through nesting habitat. From the 7th of April onwards, we set to work installing and electrifying 7 nesting pens.
On 31st March, 3 members of DCS Staff put in place the blue perimeter rope. The rope covered the same area as in previous years, encapsulating the entire colony site as well as the saltmarsh at the rear. This prevents members of the public from entering the site from either side, providing a visual barrier in order to reduce disturbance. It is incredibly important that disturbance by visitors is kept to an absolute minimum in order to prevent the potential abandonment of nests and allow birds to look after their eggs/chicks which are vulnerable to cool, wet or extreme weather.
All work was carried out following social distancing protocol. Each member of staff travelled to the site individually, and whilst working, a safe distance of at least 2m was maintained. Staff also wore gloves, and sanitization products were used and made available at all times.
This year, a total of 7 pens were constructed using the standard green poultry netting. Construction took place from the 7th May and 3-4 DCS staff were involved in construction.
Birds were observed nesting outside of the pens, so a new system involving strap fencing was used in order to quickly provide these areas with protection whilst keeping disturbance to a minimum. In order to electrify the strap fencing, the strands were attached to the pre-existing neighbouring pens. The strap fencing consisted of 6 to 7 electrified strands, supported by insulator posts at regular intervals to provide stability. A system was also used that allowed the strap fencing to be raised and lowered in accordance with the tides and predicted tide heights, where water sometimes came through the gully. This meant that damage and debris from tides could be kept to an absolute minimum, especially when we could not work with volunteers, who historically helped a great deal with fence clearing.
Electrical set-ups were the same as in previous years. Each pen had a battery, energizer and solar panel set up. Pens were turned off in the morning and on again in the evening in order to give batteries chance to recharge via solar power during the day.
Photos by Denbighshire County Council (Under licence)
Figure 2: New Strap Fencing Connection. Figure 3: Example of Strap Fencing.
Figure 4: Colour coded overlay of pen positioning recorded with use of GPS by Nigel Wild
This overlay shows the positioning of each of the pens this year, with the pens as follows:
The White lines joining the pens show where the new style strap fencing was used this year in order to close off the pens and protect nests in the gully.
The same signage as in previous years was used, and attached to the perimeter posts which support the blue rope boundary. Signage was also placed at the site where entry to the colony by visitors was previously permitted. Standard signage requests that visitors stay 30m away from the blue perimeter rope and keep dogs on leads whilst passing the colony.
In addition to this, we also put up a sign declaring changes during the COVID-19 pandemic. This sign made visitors aware that we were not allowing visitation in the same manner as in previous years, but that they were able to view the birds from outside the blue rope perimeter.
Due to COVID-19 restrictions, we did not put the visitor centre or bird hide up. Due to us not being able to allow visitors and volunteers to enter the site, there was no need for this infrastructure this year.
Viewing Platform and Boardwalk
As with last year, the new disabled access boardwalk and viewing platform was a real draw for visitors to Gronant. This new infrastructure continues to divert visitors who want to use the beach, guiding them towards signage and helping to prevent them from walking directly down in front of pens, reducing instances of disturbance.
Monitoring and Breeding Success
3.1 Key Information for 2020
The first little tern adults were spotted on the 5th May, over 2 weeks later than last year (19th April). The first eggs were then discovered 25 days later on 30th May. By the 2nd June, a total of 89 nests were recorded during a nest count. Unfortunately, not long after this count, we experienced high tides and stormy weather on 5th - 7th June, during which around 70% nests were lost. On a positive note, not long afterwards birds were seen to resume courtship behaviors, and a week or so later, relays replaced those nests originally lost (although many were far away from the fenced area and chose unsuitable sandy habitat away from the tide). It is thought that many birds which lost nests due to the storm moved on from Gronant, instead nesting at Point of Ayr further along the coastline. Historically, only a couple of LT nests had been successful there, but this year 21 were recorded, which could be attributed to such movements.
The first chicks were recorded on the 21st June, with chick activity elevated considerably by the 25th June. Unfortunately, predation pressure was high and many chicks were lost during high winds due to severe sand blow. Fledgling numbers were estimated at 31 (Excluding 1 Irish fledgling seen), but this number may be elevated if other un-ringed fledglings raised at colonies in the Irish Sea were also congregating with the group. With 89 breeding pairs, this puts the ratio of fledglings to pairs at around 0.35. Unfortunately, this figure means this season the colony has fallen short of the sustainability figure of 0.74 as proposed by Cook and Robinson (2010). Fortunately, due to the little tern being a long lived species, the lower productivity this year should be mitigated by previous very successful seasons and hopefully a much higher output next year.
Adult Little Tern Counts
Adult little tern counts were mainly carried out during high tide, when the birds congregate along the shoreline. During these counts we witnessed congregations in excess of 300 individuals.
This year, pens were not marked using the standard colour coded bamboo cane method. Due to reduced hours of cover, we wanted to ensure that nests were safe from members of the public and potential egg collectors. Instead, we created inconspicuous rock piles next to the nests, which could not be spotted easily from outside the pens. For monitoring purposes, we also split each pen into 4 sections using small pegs, which allowed us to monitor nest numbers in each section of the pen.
Nest and Clutch Counts
We carried out clutch counts once per week in order to record egg and nest numbers. Counts were carried out by 2-3 individuals at a safe distance. Ensuring multiple people were on site to do the counts meant that the count could be done more quickly and efficiently, reducing the overall disturbance time for the birds. Following a clutch/nest count, further disturbance to the birds was kept to an absolute minimum. We had to cancel counts on multiple occasions due to storm tides and high winds.
Chick and Fledgling Counts
Severe weather events interrupted regular clutch counts and our first chicks appeared a few days prior to flooding. After this, staff would individually check nests for chicks whilst turning pens on and off in order to keep disturbance to a minimum.
Fledgling counts were done using a scope outside the blue perimeter where birds gathered at high tide. We were fortunate to have a lot of help from volunteers who were able to observe the birds from outside the perimeter in accordance with social distancing measures.
Figure 5: Long Term Breeding Trend
This year, 89 breeding pairs were recorded, a figure significantly lower than in previous years. As shown in the graph below, numbers are close to those in 2005, where 87 breeding pairs were recorded and 32 fledglings. It is thought that some birds may have moved on to breed at Point of Ayr instead, following high tides and nest losses. At point of Ayr, a total of 21 breeding pairs were recorded and 28 fledglings.
Fledgling numbers over the years show a consistent ‘peak and trough’ pattern, which is more pronounced over certain periods. The trend between 2010-2017 is an example of how much fledgling numbers can fluctuate, with a distinct dip in the count of 2012. From 2013-19, fledgling output rose steadily again, seeming to counterbalance the previous shortfall. Though this year’s fledgling numbers were very low, they can be partially explained by lower numbers of breeding pairs, which are very similar to those in 2005, where a much lower fledgling count is also reflected. We are unsure why the breeding pairs figure was so much lower this year, but hope that next year brings a better turn out, mitigating the lower output this year and hitting that minimum sustainability figure of 0.74 once again. The graph below shows long term sustainability trends. The aforementioned peak and trough pattern is especially apparent when looking at breeding success figures over time.
Figure 6: Colony Sustainability. Breeding success = fledglings/pair
Other Breeding Birds
Ringed plover and oystercatcher were also observed nesting in the pens alongside the little terns. Approximately 2 Oystercatcher pairs were seen nesting and 3 ringed plover.
Little terns are vulnerable to a number of predators. Some selectively target eggs, whilst others pose a real threat to vulnerable chicks and fledglings. Staff closely monitored the colony for signs of disturbance and intervened to prevent predation where possible. In terms of aerial predators, 6 little terns/juveniles were recorded to have been predated by kestrel and peregrine, though this number is considered to be much lower than the actual predation rate, due to reduced staff and cover.
As with previous years, predation by kestrel Falco tinnunculus was a problem. This year it was of particular concern given lower chick numbers. Staff became accustomed to kestrel behaviour, and identified their most commonly used flight paths into the colony. This meant that staff could position themselves strategically in order to more successfully drive kestrels away and prevent instances of predation. Staff carried starter pistols, which proved an effective tool in deterring kestrels when attempting to enter the colony. It is thought that having less people on site may have contributed to kestrel presence. Additionally, there were also confirmed sightings of kestrels nesting nearby at the North Wales Wildlife Trust site Big Pool Wood, inland between Gronant and Talacre.
Predation by fox Vulpes vulpes has the potential to completely wipe out a colony if the correct measures are not put in place. Foxes are a particular threat to nests and chicks.
This season, we had no instances of foxes being able to enter the pens. Unfortunately, foxes were able to predate nests which were too far out to be moved within the pen system. The fox is thought to be responsible for the predation of 40 nests outside of the fencing.
Peregrines Falco peregrinus are notoriously difficult to deter, due to their speed and insusceptibility to starter pistol use. They are a particular threat to adults, fledglings and chicks.
Stoat and Weasel
Whilst no stoats Mustela erminea or weasels Mustela nivalis were sighted actually in the colony, a weasel was seen nearby. Both are capable of predating chicks/eggs, and in previous years’ weasels have been a significant problem. With this in mind, it is possible that they were also responsible for some of the predation this year.
Extreme weather has made this season for the terns particularly challenging. Storms and high winds have been a real challenge for chicks in particular, whom this year have unfortunately struggled to thrive.
High tides triggered by storms from the 5th-7th June have proved devastating to the colony. Despite the best efforts of the staff to move vulnerable nests, a large proportion of nests were covered by foam and many destroyed. Some sections of fencing were completely torn down and supporting posts snapped, meaning they had to be completely replaced. Fortunately, not long afterwards birds resumed breeding behaviours and these nests were replaced.
Photos by Denbighshire County Council (Under licence)
Figure 7: Right to left. High Tide from Storm with Foam and Fence Damage.
Whilst historically sand blow has caused some issues for the colony, this year’s almost consistent high winds have meant that severe sand blow has been a regular occurrence. Regular sand build-up has meant that nests have often been inundated by sand. Fortunately, adults were able to raise eggs and prevent them from being buried fairly well. The real issue was with vulnerable chicks being overwhelmed by sand, many perishing despite our best efforts to provide shelter. As chicks grow older, adults cannot shelter all their young. They also have to leave chicks in order to find food, and support development. In all, at least 28 chicks perished in this manner. We are hoping to come up with a new system next year which may help afford the chicks more protection, should we experience sand blow of this magnitude again.
Photos by Denbighshire County Council (Under licence)
Figure 8: Examples of Sand Blow on Site
Photos by Denbighshire County Council (Under licence)
Figure 9: Chick Which Sadly Perished Due to Sand Blow.
Ringing and Colour Ring Re-sightings
Fitting metal BTO rings and coded colour rings can prove an invaluable method of tracking and monitoring little tern movements and behaviour. Colour ring fitting was originally introduced as part of the EU LIFE+ Project (2013-2018), as unlike the traditional metal rings, they are able to be read more easily in the field, resulting in greater feedback of data. Colour rings can verify a birds age, and where the bird was originally ringed as a chick. Based on behavioural observations it is also sometimes possible to assign a gender to ring code on a particular bird.
Despite the struggles faced this year, there was an extraordinary colour ring re-sighting effort from volunteers and Little Tern Group members, with a total of 13:50:00 hours committed at Gronant alone.
This season, a number of interesting colour ring codes were recorded. One bird, ringed with 3 codeless green rings (Two green bands one leg, one green, one metal on the other) was originally ringed in 2018 as a Juvenile in Alcochete, Portugal.
The world’s oldest little tern was also re-sighted again this year, now an incredible 27 years old! For full info on all colour rings recorded, please see the appendix.
Ringing this year was more limited this year due to the COVID-19 situation. Ringing had to be carried out by two individuals from the same household, without volunteer assistance.
This year, ringers visited the site 5 times in total. The breakdown of birds fitted with metal and/or colour rings can be seen in the table below.
Figure 10: Adults and chicks trapped/ringed from the 9th to the 21st July.
Unfortunately, we were unable to carry out the work required to retrieve the geolocators this year, due to the situation with COVID-19. During colour ring re-sightings birds with geolocators have been spotted, so we are hopeful that they can be retrieved next year instead.
Beneficial disturbance can be defined as momentary disturbance to the colony, where tasks carried out promote wellbeing and allow for the collection of important data which provides insight on breeding success and behaviour. Instances of disturbance carried out under license and are minimized as much as possible, with prolonged or repeat disturbance prevented.
Nests which were close enough to pens to be saved without risking abandonment were gradually moved to higher ground and closer to pens, where they were less at risk of flooding.
Nests were moved a foot at a time, and the nest duplicated as accurately as possible, along with key ‘landmark’ stones nearby to ensure the birds easily find their nest once again.
Consistent site maintenance is paramount to the success of the colony. Keeping the fencing clear of sand this year was particularly challenging, given the frequency and severity of sand blow down on the beach. Combing the fences for debris after high tides, and removing rubbish blown onto them during high winds also had to be done regularly in order to keep fence condition and voltages optimal.
Keeping the fences voltages high, and insuring the fencing was flush to the ground were especially important in order to prevent foxes and other terrestrial predators from gaining access to the colony. Pegs were used on areas of fencing gaping at the bottom, as well as being filled in with rocks and shingle to help prevent digging.
Bird ringing this year was carried out by, father and son, Nigel and Findley Wilde. Co-habitation meant that they were able to work together inside COVID-19 protocol. Ringing was carried out with a member of staff present, who were able to advise on where most of the chicks were located, making ringing as quick and efficient as possible whilst keeping disturbance to a minimum. Any adults trapped were done so using the spring trap method employed in previous years (Duncan, Watson and Trower 2019, p. 16-17) Any ringing carried out was strictly done so during fair weather conditions.
Engagement and Social Media
Visitor engagement was significantly reduced this year due to the virus outbreak. Staff did however engage with visitors outside the blue rope and at a safe distance in order to give them information on the colony and the most recent stats.
Posts were also put out on Facebook, Twitter and Instagram in an effort to help keep people who may not have been able to leave their homes involved in the latest news at Gronant.
Figure 11: Left to right. Acrylic adult little tern and little tern fledgling in pencil produced by staff as part of social media engagement this year.
We would like to say a huge thankyou to all staff involved this year including Loggerheads and Keep Wales Tidy staff who helped with warden cover and site maintenance.
We would also like to say thank you to all of our volunteers and the NWLTG for their patience during this difficult time, and their socially distanced monitoring efforts!
Thank you to the ringing team and all involved for helping us to keep up the monitoring effort despite these difficult times and to everyone involved in the collection of colour ring re-sighting data. Nigel and Findlay are part of the Merseyside Ringing Group and have continued the work Professor David Norman has carried out over the last 30+ years.
Above all, we would like to say a huge thankyou to everyone who has been involved with and supported our efforts this year, whether it be it hands on or via social media. These really have been unprecedented times, but we hope that things will return to normal next year and look forward to being able to work with everyone who was unable to this season again soon.
Cook, A.S.C.P. and Robinson, R.A., 2010. How Representative is the Current Monitoring of Breeding Seabirds in the UK? BTO Research Report No. 573. BTO, Thetford, Norfolk, UK.
Duncan, Watson and Trower (2019) 2019 Little Tern Report.
11. Appendix: Colour Ring Re-Sighting Records 2020