Bed Site Selection by Neonate Deer in Grassland Habitats on the Northern Great Plains

1. What they did

White-tailed deer fawns spend most of their first weeks lying still and hidden in a bed, often far from their mother, until she returns to groom and nurse them. They rely on cover and camouflage colouring to avoid predators. Earlier studies of fawn beds came from forested regions. The authors looked at where fawns bed in the Northern Great Plains of South Dakota, where there is very little forest, at a time when Conservation Reserve Program (CRP) grasslands (farmland set aside as grassland under contract) were being ploughed back into crops.

• Finding the fawns. From 15 May to 10 June, 2007 to 2009, they found newborn fawns by watching for mothers behaving as they do just after giving birth (keeping alone, lowering themselves to hide, running only a short way from vehicles), then searching the area. They caught 81 fawns by hand, fitted them with expandable radio collars, and aged them from hoof growth and the state of the umbilicus.
• Finding the beds. They recorded the bed at capture, then found later beds by locating the collared fawns with radio antennas, up to 30 days of age, when fawns rely less on hiding.
• Measuring the beds. At 152 beds (one to three per fawn) and at 152 random sites nearby in the same habitat, they measured ground cover (grass, forbs, shrubs, crops, wheat, bare ground, litter), the height and density of the understory vegetation, tree basal area and tree canopy cover.
• Analysis. They compared beds of male and female fawns and of fawns of different ages, and used statistical models to find which vegetation features best separated beds from random sites.

2. What they found

Where the beds were

• 80 beds (52.6%) were in tallgrass CRP grassland, 35 (23.0%) in forested cover, 29 (19.1%) in wheat, 5 (3.3%) in pasture and 3 (2.0%) in alfalfa.
• CRP grassland in the study area shrank by about 41% between 2007 and 2009 as contracts ended. Beds in CRP fell from 66.7% to 31.6% of all beds, while beds in wheat rose from none in 2007 to 6 in 2008 and 23 in 2009.

Age

• Tree canopy cover and tree basal area at beds fell as fawns grew older. No beds were found in forested cover after about 18 days of age.
• The authors rarely found fawns older than 25 days that were not following their mothers.

Male and female fawns

• Male fawns bedded in more open spots than females: less grass (47.4% against 65.8%), lower understory vegetation (56.1 cm against 80.1 cm) and less dense understory, with more wheat, bare ground and litter.

What made a good bed

• The best model contained only the height of the understory vegetation. The odds of a site being chosen as a bed rose by 3.5% for every 1 cm of extra vegetation height.
• Density of the understory vegetation did not matter, unlike in earlier studies in warmer Iowa and Texas.
• Understory vegetation was tallest in CRP grassland (about 77 cm), compared with forested cover (75 cm), wheat (63 cm), alfalfa (47 cm) and pasture (35 cm).

Fawn deaths

• Summer deaths rose from 1 fawn in 2007 to 5 in 2008 and 12 in 2009, mainly from predation (10) and hypothermia (5). In 2009, 5 of the predation deaths and all 5 hypothermia deaths happened in wheat.

3. What they concluded

• In this grassland region, fawns choose beds with taller vegetation, which gives better concealment and insulation. CRP grassland supplied much of that cover.
• The shift from CRP grassland to wheat was directly linked to the loss of CRP, and the authors expect more fawn deaths as fawns bed in wheat, which has lower cover.
• Cool temperatures in the region may explain why dense vegetation was not chosen: less dense cover may let fawns gain more heat from the sun.
• With little permanent cover, fawns here may switch from hiding to following their mother earlier than fawns elsewhere, as a way of avoiding predators.
• Male fawns may take more risk in open beds, as male fawns tend to become active and independent earlier; this may relate to mothers defending male fawns more strongly at capture, seen in an earlier study.

6. Other technologies, skills or innovations

• Expandable breakaway radio collars on newborn fawns, located with a truck-mounted null-peak antenna system and hand-held Yagi antennas.
• Fawn age estimated from hoof growth and umbilicus condition.
• Vegetation measured with ground-cover quadrats, a modified Robel pole (height and density of understory), a 10-factor prism (tree basal area) and a spherical densitometer (canopy cover).
• Habitat mapped with ArcGIS 9.2 and checked on the ground with a Global Positioning System (GPS), with a new map made each summer.

7. Implications for conservation (from the paper)

• Managing grasslands in the Northern Great Plains to keep tall understory vegetation would give fawns cover from predators.
• Continued loss of CRP grassland, driven by lower enrolment limits and rising demand for biofuel crops, is likely to change where fawns bed and could raise fawn deaths.
• The authors suggest further summer research on fawn habitat and survival in the region.