White Oak Acorns Research Articles

Cache like a squirrel: analysis of and recommendations for long-term storage of white oak (Quercus alba) and pin oak (Q. palustris) acorns for use in wildlife rehabilitation without fat degradation

Cache like a squirrel: analysis of and recommendations for long-term storage of white oak (Quercus alba) and pin oak (Q. palustris) acorns for use in wildlife rehabilitation without fat degradation

Pulsed resources and the resource‐prediction strategy: a field‐test using a 36‐year study of small mammals

Pulsed resource environments are known for their marked variations in resource availability over space and time. Animals living in such environments usually increase reproduction after resources become available. Some small mammal populations, however, may use environmental cues that precede large crops of seeds (e.g. pollen, flowers, unripe seeds) to ‘predict' mast‐seeding events and reproduce in advance. In other words, these populations exhibit a resource‐prediction strategy based on future fitness prospects. Habitat selection might play a key role in the resource‐prediction strategy, but our understanding of habitat selection in pulsed resource environments is extremely limited. We used a 36‐year dataset on small mammal trapping and seed availability collected in Maine (USA) to test if American red squirrels Tamiasciurus hudsonicus, eastern chipmunks Tamias striatus, white‐footed mice Peromyscus leucopus and southern red‐backed voles Myodes gapperi select habitats based on upcoming resources and examine the consequences to individual fitness. Small mammal trapping was conducted in summer before seeds were available, thus trapping occurred when only the cues of an upcoming mast event were available. Using home‐range estimations and capture data, we performed resource selection analyses to assess if individuals select habitat to maximize future resource acquisitions. Using capture–mark–recapture models, we also estimated individual survival (a proxy for fitness). Our results do not support habitat selection as a mechanism underlying the resource‐prediction hypothesis, indicating that individuals do not select habitats based on the upcoming seed availability. Nevertheless, we found that white‐footed mice with home ranges in areas characterized by a greater quantity of white oak acorns have up to a 15% higher survival rate. Our empirical study advances the understanding of predator response to pulsed resources by not supporting a key mechanism thought to underpin the anticipatory responses that have been observed in many ecosystems worldwide.

Hunting and environmental influences on survival of male wild turkeys in Virginia and West Virginia

AbstractKnowledge of the effects of hunting and environmental influences on survival of eastern wild turkeys (Meleagris gallopavo silvestris) is critical to managers setting fall and spring hunting seasons. Research has shown improper season frameworks can result in unsustainably high harvest rates of adult males, affect male age structure, and result in lower hunter satisfaction. Our objectives were to estimate survival rates of males, identify causes of mortality, and relate hunting and environmental influences to male turkey survival. We captured and radio‐tagged male wild turkeys in Virginia (n = 204) and West Virginia (n = 197), USA, during 2004–2007. We used staggered entry Kaplan‐Meier models to estimate survival and Cox Proportional Hazards Models to estimate effects of predictor variables on survival. Survival was estimated for 3 distinct periods of interest: annual, fall hunting (October–January), and spring hunting (April–May). The leading causes of mortalities (209 turkeys) were legal spring harvest (42%), predation (25%), and poaching (17%). Only 8 turkeys (4%) were taken during fall hunting seasons. Confidence intervals for annual survival of 2 year‐old and 3+ year‐old turkeys overlapped; therefore, we combined adult ages into a single category (2+). Adult (2+) annual survival was 0.63 (95% CI = 0.58–0.69) and the harvest rate was 25% (95% CI = 20–29%) for the combined states. Annual survival rates for adults (2+) were greater than in most other published studies, whereas adult (2+) spring harvest rates were lower. For juvenile males, annual survival was 0.74 (95% CI = 0.68–0.79) and spring harvest rate was 7% (95% CI = 3–11%). High juvenile and adult (2+) survival may have been related to low harvest rates. Adult turkeys (2+) had 46% greater risk of dying than one‐year‐old birds and were 3.7 times more likely to be harvested than juveniles. Age, a relative phenology index (RPI; spring green‐up), and white oak (Quercus alba) acorn production were included in the top models for annual survival, spring season survival, and spring harvest risk. Increasing RPI (more foliage) decreased mortality risk and greater white oak (Quercus alba) acorn abundance increased mortality risk. Across 4 regions in the 2 states, fall survival was high (0.90, 95% CI = 0.87–0.93). The impact of fall hunting on males in Virginia was low (5% harvest rate, 95% CI = 0–9%). Overall, spring harvest had the greatest effect on male survival, although those effects were moderated by the previous fall white oak crop and the onset of green‐up in the spring.

Prescribed fire promotes acorn survival and seedling emergence from simulated caches

Prescribed fire increasingly is used to promote oak (Quercus) establishment in many hardwood forests across North America. However, how prescribed fire affects several key components of the oak regeneration process, including acorn survival and germination, is relatively unknown. Acorn mortality during a prescribed fire is likely affected by acorn dormancy, burn season, and previous burial (caching) by scatterhoarding rodents. We assessed the effect of fall and spring prescribed fires on seedling emergence for artificially cached and un-cached northern red oak (Q. rubra) and white oak (Q. alba) acorns in situ in granivore-proof exclosures through eight prescribed fires over two years at two sites in central Indiana. The odds of cached acorn emergence were 3.4–12.1 times higher following fall and spring prescribed fires than the unburned control. Red oak emergence was 1.7 times higher following fall burns than spring burns, whereas white oak emergence was unaffected by burn season. Lower winter temperatures following fall burns may have driven observed differences between burn seasons for northern red oak acorns. Our study links the oak-rodent conditional mutualism hypothesis with the oak-fire hypothesis, by suggesting that prescribed fire may produce environmental conditions that shift interactions between oaks and scatterhoarding rodents toward a more mutualistic relationship.

One acorn produces two seedlings in Chinese cork oak Quercus variabilis

ABSTRACTAlthough the early germination of white oaks has long been considered an adaptation to counter animal predation, the role of the robust radicles of white oak acorns has been largely neglected in the interaction between acorns and seed-eating animals. Here, the regeneration capabilities of the pruned radicles of intermediate oak Quercus variabilis left by the acorn-eating animals were compared to test the ‘one acorn produce two seedlings’ hypothesis stating that the remnant radicles exhibit the capability to produce normal seedlings owning to their atypical nutritional and anatomical characteristics. Our results first showed that both pruned radicle and cotyledons from single acorn successfully established seedlings, providing strong evidence on an old puzzle that the robust radicles of early-germinating oak acorns act as reserved propagules, allowing them to escape animals’ predation. Our study also suggests that much of the investment in the food reserves of an acorn may be important as a food reward for the animals that disperse the acorns, rather than simply serving as energy for the young seedling.

Effects of fertilization and crown release on white oak (Quercus alba) masting and acorn quality

Forest management practices that influence mast production in oaks (Quercus spp.) are ecologically and economically important for regeneration of future oak forests, timber products, and wildlife that consume acorns. We conducted a 10-year experiment in upland oak-hickory forests of eastern Tennessee to determine the influence of canopy release, fertilization (addition of nitrogen, phosphorus, and potassium), and their combined influence on white oak (Quercus alba) acorn production, acorn size and quality, and acorn depredation. We used a robust before-after-control-impact design where we collected pre-treatment acorn production (acorns/m2 of crown) data from 120 white oaks for 5 years, applied canopy release and fertilizer treatments and then monitored post-treatment acorn production on the same trees for an additional 5 years. Acorn production was temporally variable with 6 of 10 years being near complete mast failures (≤3.67 ± 8.52 acorns/m2 of crown). Also, production varied greatly among individual trees with 11% of trees classified as excellent producers accounting for 31% of all acorns produced, and 41% of trees classified as poor producers accounting for only 17% of all acorns produced. Canopy-released and canopy-released-and-fertilized trees increased acorn production 65% and 47%, respectively, following treatment relative to control trees, with effects greatest in trees classified as poor producers. Fertilization did not influence acorn production or size and did not consistently influence acorn quality. Furthermore, acorn depredation rates did not differ among treatments. Our results indicate crown release is an important management practice when management objectives include increasing white oak acorn production in closed-canopy conditions, whereas fertilization does not influence acorn production.

A test of the predator satiation hypothesis, acorn predator size, and acorn preference

Mast seeding is hypothesized to satiate seed predators with heavy production and reduce populations with crop failure, thereby increasing seed survival. Preference for red or white oak acorns could influence recruitment among oak species. We tested the predator satiation hypothesis, acorn preference, and predator size by concurrently measuring acorn production, mouse abundance, and white versus red oak acorn removal rates in exclosures allowing access by mice (HW), squirrels and smaller-sized vertebrates (WW), or all-sized vertebrates (C) for 12 years. Annual removal rate varied, but virtually all acorns were eventually removed from all exclosure types all years except one. Acorns were removed more slowly from HW than from WW or C exclosures, indicating that large vertebrates were not major acorn consumers, locally. Red and white oak acorn removal rates were similar except in two years, when red oak acorns were removed more rapidly. Removal slowed with increasing acorn crops, suggesting that heavy crops can “swamp” predators. Removal rate was negatively correlated with crop size the previous fall. A positive trend between mouse abundance and crop size the previous fall was evident; abundance decreased sharply the year following crop failures but not after moderate or heavy crops, suggesting that poor crops can dampen acorn predation the following year.

Should we use the float test to quantify acorn viability?

ABSTRACTThe float test is the most widely used method to discriminate between viable and nonviable acorns. It provides an objective, simple, rapid, and inexpensive test to inform experiments and management strategies dependent on quantification of viable acorns. However, the accuracy of the float‐test method is understudied. To test the accuracy of the float‐test method, during autumn of 2013 we collected 300 acorns from white oak (Quercus alba), native to our study area within the city limits of Raleigh, North Carolina, USA, and sawtooth oak (Q. acutissima), not native to the study area. An untrained observer visually inspected acorns (visual test) to assign viability subjectively and then float‐tested the respective acorn. After conducting visual and float tests, we planted the acorns in a test plot protected from predation. In the test plots, 56% of white oak acorns and 60% of sawtooth acorns germinated. Both the float test and visual methods accurately predicted viability in both oak species. However, the visual test (white R2 = 0.83, sawtooth R2 = 0.85) explained more variation in observed germination than the float test explained (white R2 = 0.65, sawtooth R2 = 0.70). Our data indicate the float test, though objective, is less accurate than an untrained observer at predicting the viability of acorns. We tested the potential for the methods to be paired to further improve prediction accuracy and determined the float test provided no additional information to visual inspections. When dissecting or germinating acorns is not possible, our data indicate that visually inspecting acorns is better than float‐testing to determine viability. © 2017 The Wildlife Society.

Tree squirrel seed predation patterns may influence American chestnut restoration success

Restoration of the functionally extirpated American chestnut (Castanea dentata) to landscapes of the eastern United States is planned with the successful propagation of a blight-resistant hybrid tree. Predicting the response of rodent seed consumers to this novel source of mast will be critical to restoration success, as rodents are important seed predators and dispersers in forests that once included chestnut. In particular, frequency-dependent foraging responses by rodents could affect the rate of spread of rare chestnuts following reintroductions. We conducted field trials to test for seed preferences and frequency-dependent selection by fox squirrels (Sciurus niger) when combinations of American chestnut and two common associates [northern red oak (Quercus rubra) and white oak (Q. alba)] were available in varying frequencies. Fox squirrels tended toward positive frequency-dependent seed predation when combinations of white oak and chestnuts were available, consuming more common mast items at a higher rate than expected based on availability. No preferences were observed between American chestnut and either red or white oak independent of frequency, but red oak was preferred over white oak. Frequency-dependent consumption of more common white oak acorns could benefit rarer chestnut during restoration, as squirrels would feed disproportionately on established white oak; however, this management strategy should only be considered following larger-scale and longer-term studies that consider impacts on white oak regeneration. Lack of preference or frequency dependence for chestnut when paired with red oak suggests that negative impacts of fox squirrel consumption on restoration will vary with the relative availability of the two seed types.

Using stable isotopes to assess dietary changes of American black bears from 1980 to 2001

We measured stable carbon and nitrogen isotope ratios in 117 hair samples from American black bears (Ursus americanus) in Great Smoky Mountains National Park, Tennessee, during 1980–2001 from live-trapped bears. We also collected hair from bears with known diets to compare with the wild bears. We hypothesized that biological factors (age, mass, and sex), food availability (hard mast and wild hogs (Sus scrofa)), and nuisance status would influence food selection by black bears and changes in their feeding history would be measureable using stable isotopes. We developed a set of a priori models using nine variables to examine changes in black bear stable isotope values. We found no support for changes in δ13C values associated with any of the nine variables we analyzed. Bears had enriched 15N in years with low white oak mast production and depleted 15N when white oak mast was abundant. Subadults had enriched 15N compared with adults and older adults. Variation in δ15N increased from 1980–1991 to 1992–2000 when hard mast production had greater fluctuations. Bears in a better physical condition appeared more likely to access foods with higher protein content. In years of low white oak acorn production, larger bears and subadults likely turned to alternative food sources. The long-term variation detected in this study was important in identifying which bears were potentially more susceptible to changes in availability of hard mast.

Acorns containing deeper plumule survive better: how white oaks counter embryo excision by rodents

Several squirrel species excise the embryo of acorns of most white oak species to arrest germination for long-term storage. However, it is not clear how these acorns counter embryo excision and survive in the arms race of coevolution. In this study, we simulated the embryo excision behavior of squirrels by removing 4 mm of cotyledon from the apical end of white oak acorns differing in embryo depths to investigate the effects of embryo excision on acorn germination and seedling performance of white oak species. The embryo depth in the cotyledons was significantly different among white oak acorns, with Quercus mongolica containing the embryo most deeply in the acorns. We found that artificial embryo excision significantly decreased acorn germination rates of Quercus variabilis, Quercus acutissima, Quercus aliena, Quercus aliena var. acutiserrata, Quercus serrata. var. brevipetiolata but not Q. mongolica. Artificial embryo excision exerted significant negative impacts on seedling performance of all oak species except Quercus aliena. Our study demonstrates the role of embryo depth of acorns in countering embryo excision by squirrels and may explain the fact that squirrels do not perform embryo excision in acorns of Q. mongolica with deeper embryos. This apparent adaptation of acorns sheds light on the coevolutionary dynamics between oaks and their seed predators.

Acorn viability following prescribed fire in upland hardwood forests

Restoration of structure and function of mixed-oak (Quercus spp.) forests is a focal issue of forest land managers in the eastern United States due to widespread regeneration failure and poor overstory recruitment of oaks, particularly on productive sites. Prescribed fire is increasingly used as a tool in oak ecosystem restoration, with the goal of reducing competition, and creating light and seedbed conditions conducive to germination and growth of oak seedlings. Yet, oak seedling establishment is dependent on the presence of viable acorns, which may be vulnerable to prescribed fire. We assessed the effect of prescribed burning and fire temperature on the viability of white oak and northern red oak acorns placed on the leaf litter surface, in the duff, or in the mineral soil during five winter prescribed burns in southern Appalachian upland hardwood forests. Fire temperatures varied among acorn plots, ranging from <79 to <371°C. After the burns, acorns were planted in trays with water-saturated vermiculite, exposed to 14 continuous hours of light daily, and maintained at 27°C on germination beds in a greenhouse. After three weeks we recorded the proportion of acorns germinating and the proportion of germinants with shoots. Our study indicated that patchy, low-intensity dormant season prescribed fire in upland hardwood forests reduced viability of white oak and northern red oak acorns located on the leaf litter surface, but did not generally affect acorns in the duff or mineral soil. Germination rates of both northern red oak and white oak acorns on the leaf litter surface decreased with increasing fire temperature. Shoot production by northern red oak germinants from acorns on the leaf litter surface (and less so in the duff), also decreased with increasing fire temperature. Acorns of both species on the leaf litter surface burned at temperatures ⩾204°C showed high mortality levels, with mortality virtually 100% at temperatures ⩾260°C. Fall burns, especially after a heavy acorn crop, could result in high acorn mortality, potentially impacting oak regeneration from seedlings for many years given erratic acorn production patterns among years and species. Frequent burning that reduces litter and duff depth could compromise availability of ‘safe sites’ where acorns are insulated from high fire temperatures. When oak ecosystem restoration is a goal, land managers should consider the timing and size of acorn crops, as well as the forest floor condition when determining the timing and frequency of prescribed burning.

Behavioural responses to acorn germination by tree squirrels in an old forest where white oaks have long been extirpated

Many plants and animals have evolved physical and/or chemical defences to protect them from a wide range of predators, and in turn these predators have also developed effective offensive strategies in morphology, physiology and behaviour to counterbalance the evasive strategies of their prey. However, little is known about how morphology, physiology and behaviour in either predator or prey respond to local extinction of their interacting partners. Interactions between scatter-hoarding squirrels and oaks provide a valuable model system to explore such questions. In an ancient forest in southwest China, where nondormant white oaks have long been extirpated, we investigated how free-ranging Asian red-cheeked squirrels, Dremomys rufigenis, manipulated acorn germination, even when they had no experiences of white oak acorns in their habitat. We also tested the food perishability hypothesis, which suggests that rapid germination of seeds can lead to loss of energy and nutrients during storage. Our results were mostly consistent with the food perishability hypothesis: like several other squirrel species in both Asia and North America, (1) the focal squirrels were able to distinguish subtle differences between dormant and nondormant acorns, with more nondormant acorns having their embryos removed and dormant acorns being hoarded more; and (2) embryo-removed acorns had significantly lower germination success. Our study suggests that embryo removal behaviour by scatter-hoarding squirrels may be an adaptive trait allowing squirrels to use nondormant acorns as a long-term food supply and such adaptive behaviour can remain unchanged even when white oaks are extinct in their habitats.

Establishment and growth of oak ( Quercus alba, Quercus prinus) seedlings in burned and fire-excluded upland forests on the Cumberland Plateau

Recurrent problems with regeneration of oaks ( Quercus spp.) have been documented across a wide range of ecosystems. In oak-dominated forests of the central and Appalachian hardwood regions of the United States, a lack of competitive oak regeneration has been tied, in part, to fire suppression in these landscapes, and managers throughout the region are using prescribed fire to address this concern. To examine fire effects on oak regeneration, researchers have generally relied on inventories or population studies of existing seedlings. These studies are valuable but do not permit examination of the role of fire in enhancing the establishment and growth of new oak seedlings stemming from oak mast events. In this study, white ( Quercus alba) and chestnut oak ( Quercus prinus) acorn mast crops serendipitously occurred in year three (fall 2005) of a landscape-scale prescribed fire experiment. We examined establishment, survival, height and diameter of new seedlings on sites on the Cumberland Plateau in eastern Kentucky. Treatments were fire exclusion, a single prescribed fire (1x-burn; 2003), and repeated prescribed fire (3x-burn; 2003, 2004, and after acorn drop in 2006), all conducted in late spring. Initial densities of newly established chestnut and white oak seedlings were statistically similar across treatments ( P = 0.42), despite fires on the 3x-burn site having occurred after acorns were on the ground. Oak seedling density was significantly predicted by oak basal area on all sites ( R 2 = 0.12–0.46), except for chestnut oak on fire-excluded sites ( R 2 = 0.04). Litter depth was less on 3x-burn sites compared to 1x-burn and fire-excluded sites, whereas canopy openness was greater on both burn treatments compared to fire-excluded sites. Seedling mortality was generally higher on fire-excluded sites compared to burn sites, especially for white oak. Oak seedling mortality in the first two growing seasons was significantly predicted by initial litter depth and open sky, with greater litter depth and lower percent open sky leading to higher mortality. In the third growing season none of the measured variables predicted chestnut oak seedling survival; for white oak, percent open sky remained a significant predictor of mortality. Initially, seedlings on the fire-excluded sites had similar height but smaller diameter; after three growing seasons there were few differences in seedling height or diameter among treatments. Our findings suggest a potential role for prescribed fire in establishing forest floor and light conditions that may enhance the success of new oak germinants, although different responses among species may suggest the need to target management for individual oak species.

Acorn storage alternatives tested on Oregon white oak

We assessed various combinations of storage factors: bag type, temperature, duration, and antifungal pre-storage treatments for white oak acorn storage, using Oregon white oak ( Quercus garryana Douglas ex Hook. [Fagaceae]) acorns from 7 seed sources. Acorn viability remained high (84%), even after 2 y of refrigerated storage, but the majority of these acorns germinated between 6 and 12 mo after entering storage. Germination during storage differed significantly by seed source. The likelihood of successful storage of Oregon white oak acorns was increased by placing washed, healthy-appearing acorns in storage at a near-freezing temperature (1.6 °C [35 °F]) soon after collection. Sealed conventional freezer bags or specialized gas-permeable plastic bags were equally effective in maintaining viability. For 6-mo storage under the best treatment combination, 77% of acorns remained viable but ungerminated in storage, compared to 89% viability prior to storage.

Frequency-dependent selection by tree squirrels: adaptive escape of nondormant white oaks

Frequency-dependent selection is theoretically predicted to have an important impact on predator–prey dynamics, but little is understood about this process in nature. We investigated oak–squirrel interactions to test the hypothesis that tree squirrels predate/disperse white oak acorns based on the frequency of their germination phenotypes (dormancy, i.e., delayed germination vs. nondormancy, i.e., immediately germinating), which in turn influences dispersal and establishment of these oaks. In Central China, we manipulated the relative frequency of dormant and nondormant acorns available to Père David's Rock squirrel (Sciurotamias davidianus) with 2 white oaks (QAA, Quercus aliena var. acutesevata and QSB, Quercus serrata var. breviptiolata) that exhibit considerable variation in acorn germination between and within oak species throughout the fruiting season. We predicted that dispersal success (i.e., the probability of a viable acorn being hoarded) of each germination phenotype would vary with the phenotype frequency and hence show either positive or negative frequency-dependent selection. We found that acorn-embryo removal by squirrels may select for the dormant phenotype but is more likely to occur for early germinating acorns. We also found that both absolute and relative dispersal success of each germination phenotype increased with their frequency in the 2 white oaks, thus demonstrating positive frequency-dependent selection. Our results reveal that the frequency of germination phenotypes can account for as much as 40.5% and 21.4% of the observed dispersal success in QAA and QSB, respectively. We show that behavioral preferences of scatter-hoarding animals could result in frequency-dependent selection in nature, and such selection may help maintain variation in germination phenotypes in prey species.

Synchronicity and Geographic Variation in Oregon White Oak Acorn Production in the Pacific Northwest

We explored geographic patterns and synchrony of Oregon white oak (Quercus garryana) acorn production over 8 years from Vancouver Island, British Columbia to Medford, Oregon. We divided our data into geographic areas: Puget-Willamette Trough, Columbia Gorge-East Cascades (Eastside) xeric, Eastside mesic, Cascade Mountain foothills, Roseburg, and Medford to compare annual acorn production among areas. We observed high within-area synchrony, but synchrony across areas was only apparent in 2004 and 2006 (high production), and 2005 (low production). Correlogram analysis indicated significant acorn crop correlation throughout the Puget-Willamette Trough, but synchrony was higher over greater distances among stands than among trees. Relationships between acorn production and mean monthly temperature or precipitation were examined with correlation analyses for each month between floral initiation and acorn maturation over 8 years of observations. Acorn production in the Puget-Willamette Trough was negatively correlated with spring precipitation, possibly due to an effect on floral processes, and winter temperature, which might relate to bud chilling requirements. In Eastside uplands, June precipitation positively correlated with current acorn production, but negatively correlated with the following year's production suggesting a climatically mediated depression by one year's production on that in the following year. Eastside production negatively correlated with precipitation in March suggesting precipitation interferes with floral processes at that time. We developed predictive linear regression models for the two analysis areas with largest sample sizes. Oregon white oak masting is similar to that in other white oaks in terms of periodicity and the effects of spring weather, but is also influenced by other weather related factors following floral induction.

Nut Selection by Captive Blue Jays: Importance of Availability and Implications for Seed Dispersal

Abstract We assessed dietary preference of 14 captive Blue Jays (Cyanocitta cristata) for different food types under different conditions of availability. In four separate feeding trials, we provisioned jays with the following: Trial 1, two nuts each of white oak (Quercus alba), pin oak (Q. palustris), black oak (Q. velutina), northern red oak (Q. rubra), and shagbark hickory (Carya ovata); Trial 2, two small and two large red oak acorns; Trial 3, two germinating and two nongerminating white oak acorns; and Trial 4, one large red oak acorn, one large white oak acorn, and one shagbark hickory nut. We used discrete choice models to describe selection under conditions of changing choice sets. Blue Jays displayed a clear preference for pin oak and strong avoidance of red oak acorns when alternative foods were available. White oak and black oak acorns were selected intermediately. Shagbark hickory nuts were never used. Correlation coefficients suggested that preference was inversely related to seed size and the proportion of seed consisting of hard seed coat. In the absence of alternative food items, small red oak acorns were readily taken, whereas large red oak acorns were mostly avoided but still used by some birds. These results highlight the importance of considering food availability when making conclusions about preference, and lend support to the hypothesis that Blue Jays can be important dispersers of even less-preferred oak species. We discuss the potential as well as the limitations for Blue Jays to act as seed dispersers, with respect to postglacial range expansion of fagaceous tree species, and in the context of present-day dispersal in regions where forests are highly fragmented.

Successful 1-y storage of swamp white oak acorns

Although acorns of the white oaks (Quercus spp. [Fagaceae]) deteriorate rapidly during storage, necessitating prompt planting of acorns in the nursery, we successfully stored swamp white oak (Q. bicolor Willd.) acorns for 1 y. After storage, stored acorns produced seedlings comparable to freshly sown acorns. In Missouri, swamp white oak acorns are difficult to obtain in sufficient quantities, so these results offer some promise for more efficient use of large acorn crops.

NUT SELECTION BY CAPTIVE BLUE JAYS: IMPORTANCE OF AVAILABILITY AND IMPLICATIONS FOR SEED DISPERSAL

We assessed dietary preference of 14 captive Blue Jays (Cyanocitta cristata) for different food types under different conditions of availability. In four separate feeding trials, we provisioned jays with the following: Trial 1, two nuts each of white oak (Quercus alba), pin oak (Q. palustris), black oak (Q. velutina), northern red oak (Q. rubra), and shagbark hickory (Carya ovata); Trial 2, two small and two large red oak acorns; Trial 3, two germinating and two nongerminating white oak acorns; and Trial 4, one large red oak acorn, one large white oak acorn, and one shagbark hickory nut. We used discrete choice models to describe selection under conditions of changing choice sets. Blue Jays displayed a clear preference for pin oak and strong avoidance of red oak acorns when alternative foods were available. White oak and black oak acorns were selected intermediately. Shagbark hickory nuts were never used. Correlation coefficients suggested that preference was inversely related to seed size and the proportion of seed consisting of hard seed coat. In the absence of alternative food items, small red oak acorns were readily taken, whereas large red oak acorns were mostly avoided but still used by some birds. These results highlight the importance of considering food availability when making conclusions about preference, and lend support to the hypothesis that Blue Jays can be important dispersers of even less-preferred oak species. We discuss the potential as well as the limitations for Blue Jays to act as seed dispersers, with respect to postglacial range expansion of fagaceous tree species, and in the context of present-day dispersal in regions where forests are highly fragmented.