The effect of human-modified landscape structure on forest grouse broods in two landscape types

(Poster)

Esa Huhta
esa.huhta@luke.fi

Natural Resources Institute, Finland
,
Pekka Helle
Natural Resources Institute, Finland
,
Vesa Nivala
Natural Resources Institute, Finland
,
Ari Nikula
Natural Resources Institute, Finland

DOI: 10.17011/conference/eccb2018/107449

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The population sizes and the breeding success of Finnish tetraonids have been decreasing for decades. In this study, the presence of a grouse hen with a brood in a landscape was used to indicate habitat-related breeding success. We combined the locations of 938 black grouse (Tetrao tetrix), 388 capercaillie (T. urogallus), and 917 hazel grouse (Tetrastes bonasia) broods after the breeding season in mid-August with landscape data by employing Geographic Information Systems (GIS) and grouse data derived from the Finnish wildlife triangle censuses conducted during 1997–2004. Two large study areas with different landscape structures; northern forest-mire area and southern cultivated area, were selected for the investigation. The presence of grouse broods was positively related to the amount of old coniferous mixed forest. Grouse broods may prefer this forest habitat because of a rich understorey cover and a rich bilberry field layer offering a diversity of insects as food. Broods had a strong positive response to the amount of forest habitat. The effect of forest fragmentation on the broods’ distribution did not increase even with decreasing forest habitat. We suggest that there are several ecological causes for the observed spatial correlations. Predation on nests and broods by generalist predators is presumably high in human modified open and semi-open landscapes. Against our expectations, the effect of landscape composition on grouse broods was more marked in the northern than in the southern study area, most likely because predator populations are more food-regulated in the north. This finding supports the alternative-prey hypothesis. Further, large drained and reforested peatland mire areas had a negative impact on grouse broods in the north. In the drainage areas, decreased availability of vegetation cover and insect food, increased predation risk, and drowning of chicks in ditches may increase brood mortality.

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INTRO:
Habitat fragmentation is important threat for biodiversity. This research summarises results of not only fragmentation, but predator-prey interactions as well in controlled environment, that may be extrapolated to real world situations.
MERITS:
Manuscript seems very straight-forward and easy to read. Theme is of high actuality and strong background are proven by references.
CRITIQUE:
Thesis supported by reference 2 is hard to be concluded from research design and measurements written in abstract, yet abstract was limited in space. No serious critique.
DISCUSSION:
Controlled research seems great. It would be even better if theory generated here, could be reinvestigated in natural environment, for example, timber forestry ecosystems.

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INTRO:
Tetraonids species populations have been declining for long time. This stydy reports the effect of human modified lanscape on nesting success of three tetraonids species in Finland. Topic suits well in to program of the ECCB 2018.
MERITS:
Main merit of this study is the impressive data, more than 2000 tetraonids broods recorded in the Finnish came and wildlife triangle counts between years 1997-2004.
CRITIQUE:
Data analysis and modelling methods could be described bit more in detail in the abstract. Now for example scale of the study remainds open.
DISCUSSION:
Topic is important and it suits well in to program of the ECCB 2018.

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INTRO:
The study investigates the breeding habitat characteristics of three different grouse species in Finland by relating brood locations to landscape data. It provides results about the general habitat requirements of the three different grouse species in combination and shows how they differ between two major study regions with unequal human influence.
MERITS:
The study investigates an important topic for conservation biology and makes use of a large dataset of grouse presence for three species.
CRITIQUE:
The study question does not become clear from the introduction section. An additional sentence at the beginning of the abstract highlighting the main question / hypothesis would assist understanding the purpose of the study.

The assumption that the presence of a hen with a brood is a proxy for breeding success is questionable to me. Rather it is a proxy for habitat/territory choice and should be formulated accordingly.

As the dataset involves three species with a large number of replicates for each it would be nice to see potential differences in habitat use between the species. However, the study does not make use of this potential and it does not become clear why.

To me the study design is not made clear enough. For example it is not clear what the response of the models was, that was modelled with the landscape data - if it is presence/absence of broods in different areas or the number of broods in areas with occurrence of broods.

Some results are not clear: For example in the sentence "The effect of forest fragmentation on the broods' distribution did not increase even with decreasing forest habitat." it is not clear to me with what it was supposed to increase. If it is the forest habitat cover then the "even" is misleading.

In addition it would be nice to have some implications for conservation biology as the study allows obvious conclusions about the habitat requirements of grouse species in Finland.
DISCUSSION:
The study investigates an important topic for conservation biology and makes use of a large dataset of grouse presence for three species. However, the abstract leaves many aspects of the methods and results unclear. I believe that most issues are just a matter of writing and the abstract could be improved by being clearer about certain aspects of the study.

The effect of human-modified landscape structure on forest grouse broods in two landscape types