Location of bumblebee nests is predicted by counts of nest‐searching queens

Abstract

* Bumblebee nests are difficult to find in sufficient numbers for well replicated studies. Counts of nest-searching queens in spring and early summer have been used as an indication of preferred nesting habitat, but this relationship has not yet been validated; high densities of nest-searching queens may indicate habitat with few nesting opportunities (meaning that queens have to spend longer looking for them). * From mid April 2010, queen bumblebees were counted along twenty transects in grassland and woodland habitats in Central Scotland, UK. The number of inflorescences of suitable forage plants were also estimated at each transect visit. The area surrounding each transect was searched for nests in the summer. * In total 173 queen bumblebees were recorded on transects, and of these 149 were engaged in nest-searching. Searches subsequently revealed 33 bumblebee nests. * The number of nest-searching queens on transects was significantly, positively related to the number of nests subsequently found. Estimated floral abundance along the transect did not correlate with numbers of nest-searching queens or the number of nests found, suggesting that queens do not target their searching to areas locally high in spring forage. * The data suggest that counts of nest-searching queens do provide a useful positive indication of good nesting habitat, and hence where bumblebee nests are likely to be found later in the year

Accounting for imperfect detection in species with sessile life cycle stages: a case study of bumble bee colonies

“…However, comparisons among studies are ultimately hampered by differences in survey efforts, and thus, differences in detection error. For example, low-intensity free searches by researchers or volunteers produced estimates of nest density ranging from 1.4 to 3.6 nests·ha −1 similar to the range of nest densities discovered by bumble bee “sniffer dogs” (O’Connor et al 2012, 2017). Both of these studies acknowledge that detection error is likely substantial for these methods.…”

“…Since colonies are the functional unit of the population for social insects such as bumble bees, studies of nesting habitat are particularly valuable for conservation planning. Yet, colonies are difficult to find, so relatively few studies have investigated the correlates of nest density compared to the numerous studies of habitat preference by foraging workers (but see examples in Harder 1986; Osborne et al 2008; Waters et al 2010; Lye et al 2012; O’Connor et al 2012, 2017). This disparity is problematic because workers are highly mobile, e.g., workers often forage up to 1 km from their colony (Greenleaf et al 2007) and may be attracted to areas rich in floral resources.…”

“…A variety of methods have been used to estimate the density of bumble bee nests across landscapes. These methods have included “free searches” in which observers haphazardly search particular habitat types for nests (Harder 1986; O’Connor et al 2012; Rao and Skyrm 2013; O’Connor et al 2017), canine-assisted searches (Waters et al 2010; O’Connor et al 2012), and concentrated stationary observation of small plots by individual researchers or distributed citizen science networks (Osborne et al 2008; Lye et al 2012). As an alternative to ground-based searches, molecular (i.e., genetic) analysis of foraging workers has also been used to infer nest density at large spatial scales (Darvill et al 2004; Goulson et al 2010).…”

“…As an alternative to ground-based searches, molecular (i.e., genetic) analysis of foraging workers has also been used to infer nest density at large spatial scales (Darvill et al 2004; Goulson et al 2010). Other studies have inferred the relative density of nests across space based on the prevalence of spring prospecting behavior by newly emerged queens (Svensson et al 2000; Kells and Goulson 2003; O’Connor et al 2017). Combined, these studies have reported considerable variation in nest densities (range: 0.1 to 50.1 nests· ha −1 ; Table 2 in Appendix 1), potentially owing to ecologically relevant differences across species, habitat types, and landscape configurations.…”

Quantifying the relative predation pressure on bumblebee nests by the European badger (Meles meles) using artificial nests

“…In contrast, grassland is mainly visited by badgers in wet conditions when foraging for their primary prey item, L. terrestris (Kruuk & Parish, ; Shepherdson et al, ). Bumblebees also utilize these two habitats, for nesting (O'connor, Park, & Goulson, , ; Osborne et al, ) and foraging (Carvell et al, ). A number of studies show that bumblebees nest at similar densities in woodland and grassland habitats in the UK (Woodland: 10.8–27.78 ± 13.33 nests/ha [O'connor, Park, & Goulson, ; O'Connor, Park, & Goulson, ; Osborne et al, ]; Grassland: 11.4–14.8 nests/ha [Osborne et al, ]), although other work has shown bumblebee and pollinator abundance is often negatively impacted by woodland (Diaz‐Forero et al, ).…”