- Predation on wader nests in Swedish Lapland [Paula Machín Álvarez]
The results showed a lower daily predation rate (DPR) in Ammarnäs in 2009 than in 2008.DPR was higher for the family Charadridae, almost twice as high, as for family Scolopacidae during 2009. Predation rates were in general higher in the beginning and at the end of the breeding season. The DPR in Ammarnäs was significantly lower than in more southern areas of Sweden and Western Europe. There was a positive relationship between numbers of observed corvids, Ravens and Hooded crows, and DPR. Plover (Charadridae) nests were to a higher extent found on slopes while nests of other waders (Scolopacidae) were situated mainly on flat or on very gently sloping ground. Predation rates on plovers increased significantly with increasing slope. No other habitat factor showed a significant relation with DPR.
I conclude that low arctic areas of northern Sweden have a higher nest success than more southern parts of the country and Europe and that this could be a reason behind the seemingly more stable or positive trends in waders numbers for northern populations compared to southern ones. However, more studies are needed in this region, especially in other years when lemming densities are higher than in 2009.
- Habitat selection and chick survival of Eurasian Golden Plovers pluvialis apricaria altifrons during a lemming peak year in southern Lapland (Sweden) [Juan Fernández-Elipe]
In Europe, populations of waders have declined during the last years and low breeding success has been pinpointed as one of the reasons behind these population declines. Low breeding success can be a result of low nest survival or low survival of young. In both cases these factors are probably related to territory quality. Hence, with this Master project I study the effects of territory quality on breeding success, relating food availability with habitat selection and describing development of chicks and predation pressure using the European Golden Plover as a model species.
- Clustering of territory occupancy as a cue for territory quality in Long-tailed Skuas [Rob van Bemmelen]
Breeding densities of Long-tailed Skuas show a strong response to rodent densities. At intermediate rodent abundances, only a subset of pairs manages to breed. It is not understood how in such years some pairs manage to breed while others pairs do not. Possibly, these breeding pairs may be more experienced and effective hunters, and/or occupy higher quality territories than non-breeding pairs. A first step in evaluating the latter hypothesis was done in this study. Territories with high or low occupancy in years with low breeding numbers were spatially clustered, whereas territory occupancy did not show spatial clustering in years with high breeding numbers. It is unlikely that this is the result of different survey intensities. Indeed, this supports the idea that certain areas hold less favorable territories. However, no further evidence was found in habitat cover, but this was probably due to the low resolution of the vegetation map. However, territory occupancy showed a positive correlation with elevation, suggesting that higher elevation provided better circumstances for breeding. This may be caused by good conditions for feeding on arthropods. You can read the report here.
- Do Long-tailed Skuas provide safety zones for Golden Plover broods? [Pablo Capilla Lasheras]
On the tundras, waders and geese have been reported to breed in association with aerial predators. This has been explained by a trade-off between protection against other (mainly mammalian) predators by the host-predator and the risk of predation by the host-predator. In southern Lapland (Sweden), Long-tailed Skuas fiercely defend their territories against intruders and may provide protection for Golden Plover broods. In this master project, this hypothesis will be explored.
- Does location within colony affect reproduction in an Arctic Skua colony in Northern Norway? [Morrison Pot]
The Central-periphery Model is the generally accepted model for explaining spatial distribution patterns of individuals with contrasting traits in seabird colonies. In this study we aimed to find out if breeding parameters in an Arctic Skua colony in northern Norway would meet the expectations of the Central-periphery Model. We therefore tested if the breeding parameters ‘laying date’, ‘number of eggs’, ‘number of hatched eggs’, ‘number of fledged chicks’, ‘chick condition’ and ‘adult female condition’ were spatially autocorrelated within the colony. We calculated the Moran’s I as an index of spatial autocorrelation of breeding parameters and used correlograms to find out whether correlation would change when distance from the nest is increased. We did not find any statistical proof for spatial autocorrelation in the breeding parameters. Neither could we find statistical proof for correlation of these breeding variables with ‘distance to center of the colony’ and ‘distance to the shore’. Because of these results we cannot exclude a random distribution of breeding parameters. A low effect size could be an explanation for not detecting any spatial autocorrelation. Also, different aspects than location of the territory within the colony may explain reproductive success of individuals like experience and nest site fidelity.
- Sexual partitioning of breeding roles in Long-tailed Skuas. Evaluating sex roles in aggressive nest defense and nest attendance for a bird with reversed sexual size dimorphism [Tim van der Meer]
Long-tailed Skuas are territorial breeders that aggressively defend their nest and chicks from intruding predators. Long-tailed Skuas are reversed sexually dimorphic and the female is larger than the male. Reversed sexual size dimorphism may have evolved to allow the sexes to fulfil different roles during breeding. To analyse role partitioning of the sexes, the breeding behaviour of Long-tailed Skuas (Stercorarius longicaudus) was studied in the Vindelfjällen nature reserve in Sweden. Long-tailed Skuas were caught for biometric measurements and were given colour-rings to be individually recognized. Based on the biometric data individuals were sexed. To evaluate the differences in aggressive behaviour between each sex aggression scores were compared. The intensity of defensive behaviour against human intruders and a stuffed Red Fox (Vulpes vulpes) as a model predator was recorded according to a categorical scoring system. Furthermore, the individual that was found breeding during territory visits was recorded as a breeding parameter. Aggression scores of individual Long-tailed Skuas against human intruders were positively correlated with aggression scores towards the model predator. Aggression scores showed seasonal variation and variation between individuals and pairs. The males were significantly more aggressive towards human intruders during the first breeding phase when the female was preoccupied with egg laying. In the following breeding phases females were significantly more aggressive towards human intruders. A trend of females being more aggressive towards the model predator was found and females made significantly more swoops and hits at the model predator than males. Females were not found to be breeding more often than males and no correlation was found for aggressive behaviour and reproductive success. The results presented here suggest that the female is the main nest defender in Long-tailed Skuas. Aggressive anti-predator behaviour is seen as a crucial component of nest defense and may contribute to ensuring reproductive success. Larger female size may be preferred for egg production and partner selection and these factors may have contributed to the evolution of sexual size dimorphism.