29.01.2018 - 16:04

A new population estimate for The Arctic fox in Iceland

Figure 1. The estimated minimum population size of the Icelandic Arctic fox during autumn. The vertical lines show 95% confidential limits, which are larger in the last years, due to the high proportion of cohorts still unknown. The population estimate was conducted by Professor Pįll Hersteinsson from 1979-2007 but after that by his successor, Ester Rut Unnsteinsdóttir. The new estimates are based on data from 2003-2015, as 12 years is the maximum life span of the species in Iceland.
Figure 1. The estimated minimum population size of the Icelandic Arctic fox during autumn. The vertical lines show 95% confidential limits, which are larger in the last years, due to the high proportion of cohorts still unknown. The population estimate was conducted by Professor Pįll Hersteinsson from 1979-2007 but after that by his successor, Ester Rut Unnsteinsdóttir. The new estimates are based on data from 2003-2015, as 12 years is the maximum life span of the species in Iceland.
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An estimate of the population size of the native Arctic fox is propublished every 3-4 years, as a part of a long-term monitoring program that is based on the collaboration between scientists and foxhunters from across Iceland. The latter voluntarily send fox carcasses for measurements and age analysis. The population size is estimated by a method called age cohort analysis that allows for estimates on the proportion of each generation that is alive each year. As the method is based on past knowledge, it is not possible to estimate the population size reliably in present time and therefore the most recent estimate goes back 3-5 years. The cohort analysis is well suited for modelling the Icelandic Arctic fox population, as the hunting pressuse is relatively stable and a reliable sample is available for measuring age, fertility and body condition each year.

The last population estimate showed that the population had grown tenfold from 1980-2008 (E. Unnsteinsdóttir 2014) but then declined by 30% from 2008-2010. This was the first decline recorded since monitoring of the species started.. The estimateintroduced here, further suggests that the population continued to decline until 2012, in total by 40%. The population then remained stable around an average 6.500 individuals,whereas the population is now estimated to have been 7.000 individuals in the autumn of 2015. The confidential limits are large in the most recent years, as the unknown proportion of the population is still high.

Several attempts have been made to identify the factors behind population limitation and regulation of the Icelandic Arctic fox. Recent papers dealing with these questions show that the positive population growth rate from 1980 was best explained with positive growth in geese and wader populations following a period of mild climate (S. Pálsson et al. 2015). Furthermore, the expansion of the Arctic fox population was not explained by increase in fertility (litter size) as is the case in many other areas of the species´ range. An increased proportion of mature individuals taking part in breeding explained, in large parts, the tenfold increase in the population. This was possible by increase in carrying capacity through favourable conditions in weather and resources (E.R. Unnsteinsdóttir et al. 2016).

Monitoring of Arctic foxes has taken place on the Hornstrandir nature reserve since 1998, including monitoring of known denning sites for occupancy and cub survival. This area is the most important sanctuary for the native population in Iceland as the Arctic foxes have been protected there since 1995. Comparison of data from old foxhunting statistics and monitoring show that the population in Hornstrandir grew simultaneously with populations in other parts of the countryafter 1980. After it gained  protection status in 1995, the Arctic fox population in Hornstrandir remained considerably stable in regards to den occupancy, but fluctuations have occurred in mortality rate. There was a severe collapse in the summer of 2014 with many foxes found dead in the spring and few pairs breeding successfully.

The reasons behind this unexplained crash in Hornstrandir nature reserve in 2014, as well as the recent decline nationwide, are unknown.  No fatal diseases are known to occur in the Icelandic Arctic fox population but a severe mercury pollution has been found in Arctic foxes living in coastal habitats of Westfjords (Bocharova et al. 2013; G. Treu et al. 2018). This makes it even more important to continue monitoring the population health of the Icelandic Arctic fox. After all, it is the only native terrestrial species and an important apex predator in Icelandic ecosystems.

The population monitoring of the Icelandic Arctic fox began in 1979 when Prof. Páll Hersteinsson (1951-2011), then a PhD student at OxfordUniversity, asked foxhunters to collaborate with him by sending him the lower jaw of every fox they killed. With the insend jaws, the hunters gave a detailed report of the location and date of the kill, sex and social status (breeding or non-breeding). By extracting the canine from the jaw, Páll could age each individual by counting annuli in the root of the teeth. Páll studied the Arctic fox and other mammals all his scientific life until he sadly passed away in October 2011.  Ester Rut Unnsteinsdóttir, Páll´s former student, has since continued his long-term study of the Icelandic Arctic fox population. First as the founder and director of the Arctic Fox Centre and, since 2013, as a mammologist at the Icelandic Institute of National History.
The Environmental agency of Iceland (UST) is responsible for wildlife management but the procedure of the foxhunting mostly takes place on the behalf of local municipalities in each region.

For further information you are welcome to contact Dr. Ester Rut Unnsteinsdóttir, Chairman of The Arctic Fox Centre and Mammal ecologist at The Icelandic Institute of Nature History

Phone: +354 5900 500, E-mail: ester@ni.is

07.07.2017 - 15:15

Hornvik June 2017

Hornvik is beautiful at this time (Ingvi Stķgsson)
Hornvik is beautiful at this time (Ingvi Stķgsson)
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Aim: to estimate the arctic fox population status in Hornvik, den occupancy and fecundity. Monitoring at breeding dens to record tourist activity and fox response to disturbance.

Participants: Ingvi Stígsson (IS, chair), Chantal Rodrigue (CA), Emma Hodson (UK), Justin Roy (CA), Daniel Rodriguez (US), Jedd Pettit (CA) and Juliann Schamel (US).

The group took off with Borea Adventures from Isafjordur to Hornvik on June 20th. Land was taken at Horn where base camp was set up. With us were two filmers from UK who were going to film a part of a documentary on Icelandic nature and wildlife. This survey in Hornvik took one week.

All known den sites were visited in order to check if they were occupied and to estimate the number of cubs (fecundity). In total six breeding pairs were confirmed in the eastern part of Hornvik this year and the litters were large, up to nine cubs. In addition, quite a few non-breeding individuals seem to be in the area, either within territories (older offspring) or at territory borders and in the beach. The area is therefore full of life, which could also be seen by numerous eggshells from cliff bird nests, lying around at the cliff´s edge. This indicates good nesting success of the seabirds too.

A tiny little cub was brought to our team by travellers who found him and took him up in order to bring him “home”. Our team tried to keep him warm and feed him but sadly the poor little cub died in Chantal's arms after many hours of rescue effort. It should be mentioned to people that they should not try to infer and “help” is not always helpful though it is always well meant.

The weather was wet and foggy the former part of the week but in the later days, the sun came out and Hornvik was as beautiful as it can be, especially in the midnight sun.

Three territories were chosen for intensive study on tourist traffic and fox behaviour within occupied den areas. We studied each den for 12 hours a day for five consecutive days. At this time, cubs are young and still relying on their mother´s milk though they are beginning to eat solid food. Both parents have to spend considerable time foraging for the big and fast growing litter. It is assumed that in June, the animals are not yet adjusted to human traffic and as the females are bound to the dens during the lactating period, the breeding foxes are more vulnerable than the others. We also estimated home range and kept an eye on fox activity within and at territorial borders.

Brief results: most pairs had large litters of 7-9 cubs and one couple hid themselves and potential offspring so well that they were impossible to follow up. We then chose another den to monitor, with more activity and visibility. Majority of the animals were of the blue colour morph but one of the breeding female was white and had nine cubs, thereof one blue. No male came to feed the cubs as proper fathers tend to do but one blue male came and visited the den site few times. As this female had white mate last year and only white cubs, this made us think that perhaps this litter was fathered by two males, the blue and an unseen white one. The blue colour morph is dominating but blue individuals can carry genes for white colour. Therefore a white couple can only have white offspring but blue or mixed pair can have mixed litters of both colour morph. Females come in heat for only a few days in March but unfortunately we could not be there at that time to follow up the mating and territory establishment this year.

The mother of nine looked tired and not in a good shape. She had still some of the winter fur on, which indicates that she was not thriving so well. She also had a swollen milk gland that must have caused pain or at least irritation. And she probably was infected by an ear mite, making her scratch her ears a lot. The male absence at the den indicates disturbance effects and this we have seen during the past years as people are becoming more interested in observing and photographing the foxes and their cubs. He can stay away to avoid human disturbance but she is bond to the cubs as she is still lactating and they rely on her totally. Hopefully she will recover quickly and we will see her story in two documentary films that are being produced this summer.

Life is not always easy at this corner of the world and it is not likely that all the cubs will survive the summer. Usually around 4-5 cubs survive until autumn in any of these territories and this year does not look different from others. Life is a struggle in the arctic and northern hemisphere and only the strongest and most resourceful individuals survive – with a bit of luck. One can only admire the strength and diligence of these hardy animals that survive the hardest arctic winter conditions. Now it´s summer and food is in abundance for the fast growing playful juveniles who have no worries of the coming future.

We thank the volunteers for their contribution and for taking their time to take care of the fox monitoring this week in Hornvik. Without their help we couldn´t get as much data and detailed information in such a short time with so little budget.

We also thank the landowners at Horn for allowing us to use their land for base and research during the time of this study.

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