Nectar larceny in the trainbearers (Lesbia, Trochilidae)

Abstract

11Many flower visitors engage in floral larceny, a suite of so-called 'illegitimate' visits in which foragers take nectar without providing pollination services. The data on prevalence of illegitimate visits among hummingbirds, as well as the total proportion of foraging and diet that such visits comprise is broadly lacking. Here, we report the occurrence of nectar larceny in both currently recognized species of trainbearers and analyze the proportion of plant visits categorized by mode of interaction as: primary robbing, secondary robbing, theft, and/or pollination. To the best of our knowledge, we provide the first published report identifying robbing in these species. We augment our original field observations using a trove of data from citizen science databases and literature. Although it is difficult to distinguish primary vs. secondary robbing and theft vs. pollination, we conservatively estimate that ca. 40% of the recorded nectar foraging visits involve nectar robbing. Males appear to engage in robbing marginally more than females, but further studies are necessary to confidently examine the multi-way interactions among sex, species, mode of visitation, and other factors. We discuss the significance of these findings in the context of recent developments in study of nectar foraging, larceny, and pollination from both avian and plant perspectives. 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26A growing list of bird species across several clades are known to forage for nectar on so-called 'illegitimate' 27 flower visits, in which flower rewards are taken without the requisite provision of pollination services. 28 Also termed 'floral larceny,' this mode of foraging is correspondingly gaining a broader appreciation as 29 an important factor shaping the ecology and evolution of plant-animal interactions (Lara and Ornelas, 30 2001; Irwin et al., 2010; Rojas-Nossa et al., 2016; Boehm, 2018). Although species such as flower 31 piercers (Diglossa, Passeriformes) are widely known to depend on nectar larceny, there are many reports 32 of illegitimate visits by hummingbirds (Lara and Ornelas, 2001; Gonzalez and Loiselle, 2016). Some 33 morphological characteristics of hummingbirds, including bill length and tomial serrations, are thought to 34 be particularly closely associated with nectar larceny (Ornelas 1994, but see Rico-Guevara et al. 2019). 35 Nearly all plants that provide nectar and pollen rewards experience larceny, most often from insects 36 and vertebrates, and many defend against it (Irwin et al., 2010). The remarkable frequency of illegitimate 37 visits necessitated the development and adoption of a more precise lexicon of larceny (Inouye, 1980), 38 which attempts to separate it into canonical modes, partly in service of conceptual clarification useful in 39 pursuit of identifying its ecological and evolutionary causes and consequences. Thus, "primary nectar 40 robbers" mechanically create a hole in flower tissue through which they remove nectar, bypassing the 41 floral opening. By contrast, "...