3270006 Notes of the SouNtOhReTSaoHusEtthAeeSarTsnEteRr nNN NNaaAttuTurUarRliaAstlLiIsSTt, Issue 6/2, 2V103o0(l.1 76):,3 N9–o4. 22 Use of Small-volume Nest Boxes by Apis mellifera L. (European Honey Bees) in Alabama Suzanne Prange1,2,* and David H. Nelson1 Abstract - Previous studies have documented that cavities < 10 liters are consistently rejected as nest sites by Apis mellifera (European honey bees). During a study of Glaucomys volans (southern flying squirrel) ecology in Alabama, however, honey bees occupied a total of 10 nest boxes with volumes of 5–6.7 liters. These observations are significant because they represent the smallest documented cavity volume accepted by honey bees, and also because they lend support to the theory that minimum acceptable cavity volume varies geographically. Small volume cavities may be accepted in the southeastern United States due to milder climates, a paucity of natural cavities, genetic differences in honey bees among regions, or some combination of these factors. Consequently, there may be increased potential for competition between honey bees and other cavity-nesting species in the Southeast. Apis mellifera L. (European honey bees) establish new colonies by swarming. During the swarming process, a new queen is produced and the original queen leaves the parent hive with approximately half of the colony. The success of the new colony is highly dependent upon the swarm’s ability to locate an appropriate nest site. Nest sites typically consist of a cavity within a tree or man-made structure. The criteria by which honey bees select nest sites have been extensively investigated (Rinderer et al. 1982; Schmidt and Hurley 1995; Seeley and Morse 1976, 1978; Villa 2004). A critical criterion is that of cavity volume. A minimum cavity volume is necessary to accommodate an adequate amount of honey to sustain the colony throughout winter, whereas energy requirements of nest defense, labor, and homeostasis may dictate upper limits of cavity volume (Seeley 1977). Several authors have suggested that the minimum acceptable cavity volume varies geographically, with smaller volumes accepted in milder climates (Morse et al. 1993, Seeley and Morse 1978, Villa 2004). Regardless of geographic location, however, cavities with volumes < 10 liters have been consistently rejected in choice studies (Jaycox and Parise 1980, 1981; Rinderer et al. 1982), and we are unaware of reports of natural nests with volumes below this threshold. In this paper, however, we document honey bee acceptance of nest boxes with volumes < 10 liters in southern Alabama. Possible reasons for this occurrence and potential implications are discussed. We constructed 100 nest boxes, originally intended for occupancy by Glaucomys volans L. (southern flying squirrels), similar to those described by Sonenshine et al. (1973). Nest boxes had internal dimensions of 15 x 15 x 30 cm (total volume = 6.7 liters) and were constructed of 2.5-cm thick bald cypress wood. We placed a circular entrance (3.1-cm diameter) on the side of the box, approximately 5 cm from the top and rear (Fig. 1). Our study area was a 6.0-ha oak-pine woodland in Mobile County, AL (Cottage Hill Park). Canopy species consisted primarily of Pinus palustris Mill. (longleaf pine), Quercus hemisphaerica Bartr. (laurel oak), Q. virginiana Mill. (live oak), P. taeda L. (loblolly pine), and Q. falcata Michx. (southern red oak). We used a grid system with 25-m intervals and hung the boxes 3–4 m above the ground on a suitably large tree (􀂕 10 cm dbh) nearest each grid point. We checked the boxes sporadically (approximately monthly) from January 1991–May 1991 and regularly 370 2007 General Notes 371 (every 2 weeks) from June 1991–May 1992 for flying squirrel occupancy. We also noted the presence of other species, both vertebrate and invertebrate, including honey bees. For all species, we documented the number and gender (where possible) of individuals present. Additionally, we made observations regarding nest construction for all species, and took detailed notes regarding nest size and materials used (Prange and Nelson 2006). We checked nest boxes primarily during the morning hours (0700–1200 h). Honey bee swarms were observed on the study site in late spring and early summer. From April–June 1991, scouts were observed inspecting 12 different nest boxes. Most observations were made during routine nest-box checks, although some occurred while conducting other surveys (e.g., small-mammal trapping) on the study site. The exact time of these observations was not noted, but the majority took place during the morning hours. When bees were observed during nest-box checks, we proceeded directly to the next box, without disturbing them. Each box was observed being scouted on only 1 occasion; the next time the boxes were examined, the scouts had either left the vicinity or nest construction had begun. Seven boxes were chosen as nest sites, and colonies had been established (1 in April, 1 in May, and 5 in June). All nest boxes were uninhabited by flying squirrels or other species at the time of Figure 1. Nest box in the process of being occupied by European honey bees. 372 Southeastern Naturalist Vol. 6, No. 2 honey bee occupation. However, one box contained an abandoned flying squirrel nest approximately 8 cm in depth, making the total volume available to bees approximately 5 liters. Colonies were removed to a private apiary in August. All nest boxes were filled to capacity with combs, and in 2 cases, combs were also constructed outside (attached to the bottom) of the box. The following spring, 3 boxes (1 in April and 2 in May) were used by honey bees, 2 of which were occupied by bees the preceding year. Total use during the second year is unknown, however, because our study concluded in May 1992. Minimum acceptable cavity volume apparently varies geographically, and has been shown to be smaller in the southeastern United States than in harsher climates. Of 11 swarms offered a choice of 10-, 40-, 70-, and 100-liter cavities in New York, no swarm accepted a 10-liter cavity, whereas all other sizes were accepted (Seeley 1977). Based on these observations and volumes of natural nests in the same area, Seeley and Morse (1978) concluded that European honey bees prefer cavities with volumes of at least 20 liters. In a choice study in Louisiana, however, swarms accepted cavities with volumes ranging from 10 to 40 liters, with no apparent preference between these extremes (Rinderer et al. 1982). Villa (2004) also documented use of both 13- and 31-liter cavities in Louisiana. Although 31-liter cavities were chosen more frequently, Villa (2004) reported that preference for larger cavities was less pronounced than that observed in New York (Seeley 1977), Illinois (Jaycox and Parise 1980,1981), and Arizona (Schmidt and Hurley 1995). In south-central Florida, 10.2–13.2-liter nest boxes (originally intended for squirrel use) were occupied by 26 honey bee colonies over a 5-yr period (Morse et al. 1993). The reduction in minimum acceptable cavity volume in the Southeast may be in part due to milder climates and a concomitant reduction in the volume of food needed for over-winter survival. Overall, 31% of the hives in nest boxes in southcentral Florida survived at least 1 winter, and 1 colony persisted for 33 months (Morse et al. 1993). We cannot comment whether our nest boxes held enough honey to sustain a colony throughout winter because colonies were transferred to an apiary by autumn. The extension of the comb beyond the confines of the nest box, however, suggested that nest box volume was limiting. Morse et al. (1993) also observed a comb on a 13-liter nest box and noted that external comb construction was a rare behavior for honey bees in nest boxes or other human-constructed hives. If these boxes were too small to house sufficient stores of honey, then their acceptance as nest sites was likely due to factors other than climate. Southeastern pine and pine-hardwood forests typically offer fewer cavities than northern hardwood forests (Land et al. 1989, Twedt and Henne-Kerr 2001). Therefore, acceptance of cavities below optimal size may have resulted from a paucity of natural cavities in this region (Morse et al. 1993). A genetic basis for geographic differences in minimum acceptable cavity volume is also possible. Milder climates and/or reduced cavity availability in the Southeast may represent selective forces favoring greater plasticity in cavity-volume choice. However, Morse et al. (1993) pointed out that in south-central Florida, a number of beekeepers were migratory, moving their bees between Florida and various northern states each year. On this basis, they concluded that genetic isolation of feral honey bee populations in Florida was doubtful, and small-volume cavity use was therefore likely not a genetically derived behavior. 2007 General Notes 373 Regardless of the initial reason for the acceptance of small-volume cavities, honey bees occupying smaller cavities will produce smaller swarms because swarm size is proportional to the size of the parent colony. Swarm size could in turn be proportional to the volume of the swarm’s future home, but there is little evidence in support of this relationship. No correlation between swarm size and choice of cavity volume was observed in Arizona (Schmidt and Hurley 1995), Louisiana (Villa 2004), or New York (Seeley 1977), although Seeley (1977) cautioned that this relationship might not hold for very small swarms, as swarms with < 1000 bees rejected nest boxes that larger swarms accepted (Lindauer 1961). In Louisiana, Rinderer et al. (1982) found a significant correlation between swarm weight and volume of accepted cavities, but after omission of the largest swarm no correlation remained. It should be noted, however, that the lack of correlation observed in choice studies does not negate the possibility that smaller swarms are simply capable of accepting cavities with volumes that would not accommodate larger swarms, when better choices do not exist. Our observations supported the theory that minimum acceptable cavity volume varies geographically, but also suggested that even smaller cavities may be accepted in the southeastern United States than previously believed. This should not be misconstrued to imply that honey bees in the Southeast prefer smaller cavities. In our study, as well as that of Morse et al. (1993), no alternatives were provided. Although to the best of our knowledge this is the first documentation of European honey bees accepting cavities < 10 liters in volume, we do not know whether the volume of our boxes was sufficient to sustain the colonies overwinter. Competition between honey bees and other cavity-nesting species has been previously reported (Jensen et al. 1995, Thorstrom and Lind 1999). Because southeastern forests, particularly those managed for timber, may be deficient in snags and, therefore, cavities (Land et al. 1989, Twedt and Henne-Kerr 2001), increased competition for limited nest sites may be a significant concern. Twedt and Henne-Kerr (2001) employed nest boxes to enhance breeding-bird density in managed cottonwood forests in Mississippi and reported that 7 of 13 (54%) of their 16.5-liter boxes were usurped by honey bees. Competition for limited cavities will be intensified if honey bees commonly accept small-volume cavities, thereby increasing the range of species with which they compete relative to more northern latitudes. Increased competition might force swarms to move further to find suitable nest sites, which could lead to a decline in swarm survival and a reduction in colony densities. Alternatively, where honey bees are the stronger competitor, they may reduce the density and/or diversity of other cavity-nesting species, as well as the effectiveness of programs designed to enhance species density (Twedt and Henne- Kerr 2001). At the extreme, honey bees may even impede recovery efforts for threatened or endangered species, such as Picoides borealis (Vieillot) (Redcockaded Woodpecker). The intensity of competition could be reduced, however, by forestry practices that retain a suitable number of large hardwood trees and snags to accommodate cavity-nesting species in this region. An additional concern is the immigration of A. m. scutellata (Africanized honey bees). Africanized honey bees currently occur in the Southeast in Texas, Oklahoma, Arkansas, Louisiana, and Florida. They are well established in Florida, occurring in 14 counties, and their discontinuous spread across the Gulf Coast states was likely human-assisted. The invasion of the remainder of the Southeast 374 Southeastern Naturalist Vol. 6, No. 2 seems imminent. Africanized honey bees differ from their European counterparts in that they are more defensive of their colonies, exhibit less selectivity in terms of nest sites, and put more energy toward brood production than food storage and consequently swarm more often. Their effect on resident honey bee populations will be, at least in part, a function of the availability of resources and the degree of overlap in resource use. Africanized honey bees appear to utilize small cavities. Median volume of cavities in Botswana, Africa, was 17 liters (Schneider and Blyther 1988), and the modal volume was 10–20 liters near Chiapas, Mexico (Ratníeks et al. 1991). In a choice study, however, Rinderer et al. (1982) concluded that minimum acceptable cavity volume was 20 liters. Conversely, Schmidt and Hurley (1995) reported that all volumes offered (13.5, 24, and 31 liters) were accepted, with no apparent preference. Although choice studies have produced disparate results, reports of natural nests of Africanized honey bees are supportive of their ability to utilize smallvolume cavities. If use of small-volume cavities is also common for European honey bees in the Southeast, then resource overlap, and consequently competition, may be higher for Africanized and European races than previously believed. Furthermore, in forests where cavities are limited, the behavioral attributes of Africanized honey bees may lead to the displacement of European honey bees, particularly if they are already existing under suboptimal conditions (i.e., accepting cavities with volumes lower than preferred). In a coastal prairie landscape in Texas, European colonies were fragmented, and their overall density was reduced approximately 5 years after the arrival of Africanized honey bees (Baum et al. 2005). In areas where nesting resources are limited, forestry practices that maintain or enhance cavities may reduce the impact of Africanized honey bees on European honey bees, as well as other cavity-nesting species. Further research is needed to determine the frequency at which small-volume cavities are accepted by European honey bees in the Southeast, the minimum cavity volume which can sustain a colony overwinter, and whether small-cavity use results in increased competition with other cavity-nesting species in this region. Acknowledgments. We are grateful to the Mobile Parks Department for access to the study site and the Environmental Studies Center for use of their facilities. We also thank the individuals who assisted with fieldwork: D. Biggs, T. Legarduer, and L. White-Buchanan. Literature Cited Baum, K.A., W.L. Rubink, M.A. Pinto, and R.N. Coulson. 2005. Spatial and temporal distribution and nest site characteristics of feral honey bee (Hymenoptera:Apidae) colonies in a coastal prairie landscape. Environmental Entomology 34:610–618. Jaycox, E.R., and S.G. Parise. 1980. Homesite selection by Italian honey bee swarms, Apis mellifera ligustica (Hymenoptera: Apidae). 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Annals of the Entomological Society of America 97:111–116. 1Department of Biological Sciences, University of South Alabama, LSB 124, Mobile, AL 36688. 2Current address - Ohio Division of Wildlife, 360 East State Street, Athens, OH 45701. *Corresponding author - sprange@mcgrawwildlife.org.