Creepy-crawlies in a seabird’s nest

Creepy-crawlies in a seabird’s nest

Top image: Research assistant Gry Gasbjerg hoovers an eider’s nest at Storholmen. Photo: Steve Coulson/UNIS.

There have been few scientific investigations into the invertebrate fauna of bird nests in the Polar regions. Now a study done by scientists from UNIS, NINA and NPI can shed some more light on the life of insects and mites in bird nests on Svalbard.

9 July 2009
Text and photos: Steve Coulson, UNIS associate professor in Terrestrial Ecology

There are over 500 species of insect, mite and spider recorded from Svalbard, most of which live in the thin organic soils or under rocks. However, in many areas of the world bird nests contain a rich and diverse fauna with insects and mites present in very great numbers, often many hundred of individuals per nest.

Few studies of the invertebrate fauna of bird nests
The nest habitat may provide several advantages for these animals, for example a mild thermal microclimate during the incubation period due to the breeding birds occupying the nest as well as a rich nutrient input in the form of guano, food scraps and, for ectoparasites, the adult birds and chicks themselves.

However, there have been few studies of the invertebrate fauna of bird nests in Polar regions. In addition, the role of bird dispersal in creating Arctic soil invertebrate diversity has recently attracted increased attention. It is likely that no insect or mite species survived on Svalbard during the last glaciation and that the current fauna has colonised Svalbard during the past 10,000 years. Suggested routes by which this fauna might reach the isolated Svalbard archipelago include rafting on ocean currents and being blown here by the wind but recent studies suggest that bird dispersal may be more important for soil invertebrate dispersal than has been previously accepted.

Hitchhiking to Svalbard
In any event, it is clear that phoresy (hitching a ride on another animal) is important for the geographic dispersal of soil invertebrates and that the first point of arrival for many dispersing invertebrates is likely to be the nest. Therefore bird nests with high nutrient input and buffered microhabitat temperatures may assist the initial establishment of mites and insects dispersing to High Arctic latitudes.

Nonetheless, despite the considerable importance and distinctiveness of the seabird nest invertebrate fauna, there is comparatively little information documented and nothing from High Arctic localities. During July 2007 the nests of common eider duck (ærfugl), kittiwake (krykkje) and glaucous gull (polarmåke) were searched for insects, mites and spiders in collaboration with the MariClim and COPOL seabird projects. The results of this fieldwork were recently published in the journal Polar Biology.

Sampling took place in Kongsfjord during spring 2007 at three kittiwake colonies, from common eider nests on Storholmen and one glaucous gull nest. Kittiwake nests were reached by ladder which was something of a challenge in itself. Once the nest had been accessed, the contents were sampled by an electric pooter, a sort of miniature vacuum cleaner.

Most pooters are mouth-operated suction types, the animals being sucked up into a collected tube. However, an electric pooter was employed in this case since using the normal system of sucking up the animals from the nests was likely to be somewhat unhealthy. After all, an unfortunate entomologist in the 1950’s found adult insects emerging from his nose several months after accidentally sucking up their eggs while using a mouth-operated pooter on fieldwork.

Field work results
The invertebrate community sampled in this study was meagre, consisting of seven species of mite (midd) and a bird flea (loppa). The bird flea is a common ectoparasite of birds and has been recorded previously on Svalbard. Soil mites have not previously been recorded from the nests of black-legged kittiwakes, glaucous gulls or common eider nests. In this study we observed seven species of mite more commonly associated with living in the soil.

The mite faunas of the nests of black-legged kittiwake and common eider were similar but nonetheless reflected the different locations of the nests, that is on a cliff ledge or a shallow scoop in the soil; soil mites being more common in the common eider nests while a mite common in littoral (sea shore) habitats was found in the nest of the glaucous gull. That no springtails (spretthaler) were found was surprising as they might have been expected in the common eider nests.

The lack of insect and mite species diversity is probably the result of the unique habitat of the nest and the challenges this represents. Bird nests form a specialised microhabitat with periodic high nutrient input and often a diverse invertebrate community.

The nesting seabirds abandon the nest at the end of the breeding season and the length of nest occupation is species specific. The common eider leave the nest after between 25-30 days since the young wander from the nest soon after hatching. Glaucous gulls and black-legged kittiwakes however, occupy their nests longer, up to 120 days until fledging.

Hence, invertebrates establishing in the seabird nests are required not only to survive the period that the birds are on the nests but also the significant period when the nest is unoccupied.

Conclusion
In conclusion, the microarthropod fauna of nests of black-legged kittiwake, glaucous gull and common eider on Spitsbergen is sparse. Nonetheless, seven soil mite species not previously recorded from nests of these seabirds were identified.

We hypothesized that the fauna might comprise of specialised microarthropod species due to i) the distinctive environment of the nest and ii) favourable congenial conditions in the nest facilitating the establishment of new species linked to bird dispersal of microarthropods. We did not find evidence to support this but a Russian team looking at the mite fauna of snow bunting nests recently found two species so far only known on Svalbard from these nests so neither hypothesis can as yet be confirmed or excluded. The next step is to extend this study by sampling a greater number of nests around Kongsfjord, possibly as a masters student project.

Acknowledgements
The authors thank the MariClim, COPOL and BIRDHEALTH projects for assistance in accessing the nests, Gry Gasbjerg during the fieldwork and María Luisa Ávila Jiménez in the laboratory. Adult fleas kindly identified by Dr. Robert E. Lewis.

Reference
Coulson S.J. (UNIS), Moe B. (NINA), Monson F. and Gabrielsen G.W. (NPI) 2009. The invertebrate fauna of High Arctic seabird nests: the microarthropod community inhabiting nests on Spitsbergen, Svalbard. Polar Biology, 32 (7) 1041-1046.

Bird cliff, Blomstrand, Kongsfjorden

Bird cliffs are easily identified by the green grass areas on the mountain side. The kittiwake favors this cliff at Blomstrandøya in Kongsfjorden. Photo: Steve Coulson/UNIS.

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