Selection of bed-sites by roe deer Capreolus capreolus fawns in an agricultural landscape

1. What they did

Roe deer are “hiders”: for their first weeks, fawns lie still and alone, away from their mother, and rely on cover to stay unseen by predators. The authors wanted to know where fawns bed down in a farming landscape, how well hidden they are, and how this changes as the grass and herbs grow over the summer.

They worked on Storfosna, a small island off the coast of central Norway, with a fine mosaic of heather moorland, abandoned meadows, hay and silage fields, and small patches of woodland. Red foxes were absent from the island, but fawns were killed by domestic dogs and cats, and people were always around.

• Finding fawns. From 1992 to 1994 they captured and radio-collared 245 newborn fawns. Fawns were radio tracked about every 2 to 3 days and approached to within 5 m, so the habitat they lay in could be recorded.
• Measuring bed-sites (1992 only). For fawns young enough not to run off, or being recaught for weighing, they went close enough to see the fawn. They measured the height of the herb and shrub layers, and the furthest distance from which the fawn could be seen at 35 cm above the ground (about a fox’s eye height) from each of the four compass directions. The average of these four was their visibility measure.
• Comparing use with what was available. They compared the habitats fawns lay in with the habitats available in each family’s home range. Siblings were pooled, because they all depend on their mother’s home range. They also compared fawns born before the peak of the birth season (23 May) with those born after.

2. What they found

Bed-site cover

• Herb height, shrub height and visibility all differed between habitats. Fawns in farmland lay in the tallest herbs (about 0.50 m) with almost no shrubs, and were the least visible (about 0.29 m on average). Fawns in coniferous woodland had the tallest shrubs (about 1.84 m).
• Over the summer, herb height at bed-sites increased, shrub height decreased and fawns became harder to see. The same trends appeared when comparing fawns of similar age in May and June, so the change came from the growing vegetation, not from fawns getting older.
• Fawns were very well hidden in every habitat. The average visibility of about 0.5 m means a predator would have to come within a circle of about 0.79 m² to see the fawn, and in many cases the fawn could not be seen at all.

Habitat use through the summer

• Use of coniferous woodland declined over the summer, and use of deciduous woodland and meadows increased.
• Use of farmland rose to a peak in late May and early June, when the grass was tallest, and then dropped after the first grass was cut for silage. Moorland showed the opposite pattern.

Habitat selection

• Fawns did not use habitats in proportion to what was available. Over the whole period the ranking was meadow, moorland, coniferous woodland, deciduous woodland and, last, farmland, which was avoided.
• For fawns born before the peak of the birth season, the ranking was coniferous woodland, deciduous woodland, meadow, moorland and farmland. They significantly avoided farmland and favoured habitats with evergreen or shrub cover.
• Fawns born after the peak showed no clear preference or avoidance of any habitat.

3. What they concluded

• Roe deer fawns bedded in every habitat, including pastures and even vegetable gardens, and always found good cover. Fawns can make use of small patches of uncultivated habitat in a farming landscape.
• Habitat use follows the growth of the vegetation. Early in the season, when grass is short, fawns lie where evergreen plants and shrubs give cover. Later, once herbs and grass have grown, good cover is everywhere and choosing a habitat is no longer necessary.
• Early avoidance of farmland may be because short grass gives no shelter from cold rain and no cover for a fawn walking or suckling beside its mother, which could lead a predator to it. Other studies found that fawns in farmland suffered the most red fox predation.
• Late May and early June, when fawns used fields most, is also when many have not yet developed a flight response and are at risk from grass mowers.
• Because fawns use all habitats, a predator has to search everywhere, which makes searching less efficient. The authors could not tell whether this is a deliberate strategy or simply because there was good cover everywhere.

6. Other technologies, skills or innovations

• Radio collars on newborn fawns, located by radio tracking every 2 to 3 days.
• A simple field measure of how well hidden a fawn is: the furthest distance from which it can be seen at fox eye height (35 cm), from four directions.
• A digital habitat map of the island in ArcGIS, and home ranges from radio locations (minimum convex polygons).

7. Implications for conservation (from the paper)

• Roe deer fawns are vulnerable to farm machinery, and understanding where they bed in farmland may help produce recommendations to reduce losses.
• Late May and early June, when fawns used hay and silage fields most and many would not yet flee, was the riskiest time for mowing deaths.