Food Habits

Feeding

Main foods taken

Variety of insects and plant matter (acorns, nuts, etc.; Bent 1948, Martin et al. 1951, Anderson 1976).

Microhabitat For Foraging

Forage by hopping over bark of trunk and main branches of trees, moving downward as well as upward. Sometimes reach the ground looking for food (Bent 1948). May search leaf litter for fallen beech mast (TCG). Mostly use trunk, limbs, and inner parts of branches (Grubb 1982). Large branches (> 7.5 cm diameter) preferred to smaller ones (Willson 1970); all branch surfaces (top, sides, and bottom) explored intensively (Grubb 1982).

Males and females forage at different heights and substrate types in ponderosa pine (Pinus ponderosa) forest in Colorado; females forage above males and on smaller branches (McEllin 1979b). In deciduous woodlots in Ohio, males and females forage on branches of similar size (Grubb 1982). Likewise, in an aviary no sexual differences in selection of branch sizes when foraging (Pierce and Grubb 1979).

Lower temperature and higher wind velocity bring significant changes in foraging height (lower), substrate type (larger branches), and tree species used for foraging (Grubb 1975); also use less exposed parts of the home range and spend more time stationary, with more stops and slower travel (Grubb 1977, 1978).

Food Capture And Consumption

While foraging, often chip away bark with beak to reveal food hidden in crevices; also probe bark crevices (McEllin 1979b). When individuals find a food item they often wedge it into a bark crevice and hammer with the bill to open or tear it apart.

During winter, proportion of time spent foraging peaked during middle of day, a time when the birds were least vigilant for predators (Elliott 2005).

Males more vigilant when foraging alone than when in the company of females. Females, however, which are socially subordinate to males, more vigilant when foraging in pairs with males than when alone (Waite 1987).

Pygmy Nuthatches, by comparison, forage in large flocks (up to 100 birds) and are generalized foragers, using the entire tree including the underside of branches, twigs, needles, and trunk (Bent 1948, Bock 1969). Brown-headed Nuthatches also forage in flocks (6–25 birds) and are known to use tools while foraging—they sometimes employ a scale of pine bark as an extension of the bill or as a wedge to remove other bark scales (Morse 1968). Eurasian Nuthatches resemble White-breasted Nuthatches very closely in where and how they search for food (Matthysen 1998).

Diet

Major Food Items

Animal food includes locust seed weevils (Spermophagus robiniae), round-headed wood borers, leaf beetles, tree hoppers, psyllids, scale insects, ants, larvae of gall flies, eggs of plant lice and of fall cankerworms, oyster scale (Lepidosaphes ulmi), larvae of the gypsy moth, and forest tent caterpillars (Bent 1948). Anderson (1976) found this species feeding on representatives of Pentatomidae (Hemiptera), Chrysomelidae, Elateridae, Buprestidae and Curculionidae (Coleoptera), Forficulidae (Dermaptera), Formicidae (Hymenoptera), Psocoptera and Araneida.

Quantitative Analysis

Almost no data from breeding season; needs study.

Winter diet (n = 20 nuthatches) in Illinois woodlots comprised the following percentages of animal foods: Orthoptera 2.9%, Hemiptera 3.0%, Homoptera 0.3%, Coleoptera 6.5%, Lepidoptera (larvae) 2.7%, Hymenoptera (adults) 7.2%, Hymenoptera (larvae) 1.1%, Araneida 1.8%; total animal food 28.2%. Also different seeds: mast (mostly Quercus sp.) 6.6%, corn (Zea mays; presumably gleaned from nearby fields) 49.7%, Helianthus sp. 5.5%, Crataegus sp. 0.3%, Triticum aestivum 5.7%, Vitis sp. 0.1%; total plant food 71.8% (Williams and Batzli 1979). Proportion of seeds in diet: 68% in winter, 48% in spring, none in summer, and 29% in the fall (Martin et al. 1951).

Food Selection And Storage

During fall and winter, individuals regularly scatterhoard food, i.e., they disperse stores throughout their territory, using each storage site only once (Bent 1948, Petit et al. 1989, Woodrey 1991). Caching behavior has been studied only with supplementary food in feeders. Food is stored in bark crevices on the trunks of large trees and on the underside of branches, and is often covered with either a piece of bark or rotten wood, lichens, snow, or moss (Kilham 1974, Petit et al. 1989). Trees selected for caching have especially furrowed bark; males usually store food on the trunk, while females use various sites (Woodrey 1991). Males cache food an average of 13.5 m from a feeder and 5.8 m above the ground, while for females these values are about the same.

Handling time is important in a nuthatch’s decision whether to store or eat a particular food item (Woodrey 1990). Males spend an average of 22.0 s handling shelled sunflower seeds while caching, 52.0 s handling unshelled seeds; females, 27.0 s and 44.0 s, respectively. On average, nuthatches cached significantly more sunflower seeds without a shell than those with a shell (12.7 shelled seeds vs 8.5 unshelled seeds/h for males, and 22.2 shelled seeds vs. 19.8 unshelled seeds/h for females). Females cached significantly more seeds of either type than did males, and they transported shelled seeds significantly farther than did males. Caching is most intensive early in the day and decreases later (Waite and Grubb 1988a). When beechnuts are available, they are cached intensively (TCG, VVP).

Red-breasted Nuthatches wintering in an Ohio woodlot cached a mealworm once every 2.6 min, on average (Grubb and Waite 1987). The Eurasian Nuthatch is also known to cache food intensively in autumn (Moreno et al. 1981, S. Nilsson pers. comm., VVP). The nuts of shrub pine (Pinus pumela), available only in fall, were found in the diet of nestling Eurasian Nuthatches the following spring, which supports the idea that these nuthatches are long-term hoarders (VVP).

Over the course of a winter, female Eurasian Nuthatches that had previously cached sunflower seeds retrieved and ate more seeds when temperatures were colder than when warmer (Nilsson et al. 1993). This relationship leads to the conclusion that the birds refrained from using their stored food resources during more benign weather, husbanding them for cold periods. They might have done this in any of three ways. First, they could have noticed seeds by chance in all sorts of weather, but not taken them out of their storage places when it was warmer. Second, they could have found seeds by chance in all kinds of weather, but searched for them harder in cold weather. Third, they could have known the locations of all the seeds all the time and just refrained from retrieving them in warmer weather. It would be interesting to know which alternative or alternatives was or were correct. Incidentally, this prudent use of caches is a clear benefit of being territorial. No other nuthatch except the mate is around to eat seeds that are being saved for when they might really be needed.

Nutrition And Energetics

Cold temperatures and/or wind do not retard the growth of induced rectrices (see Grubb 1989) of individuals maintained experimentally on unlimited food. This suggests that the nutritional status of nuthatches does not depend on cold temperatures and wind, without consideration of food supply (Zuberbier and Grubb 1992). Access to bird feeders improves the nutritional condition of wintering nuthatches (Grubb and Cimprich 1990, Doherty and Grubb 2003).

In a mate-removal experiment, male White-breasted Nuthatches food-deprived for two hours before roosting time sang less and foraged more the following morning in the temporary absence of their mate than did males not food-deprived before going to roost. These results supported dynamic programming models of male behavior based on the state of energy supply (Elliot 2005).

Metabolism And Temperature Regulation

Nuthatches of unspecified sex were heaviest and carried more fat in winter than in midsummer (Liknes and Swanson 1996). They were most cold-hardy during winter (lowest basal metabolic rate, BMR, and highest peak metabolic rate, PMR) and about equally cold-hardy throughout the rest of the year except in late summer when they became hypothermic at higher heliox temperatures. The differences in BMR and PMR between winter and midsummer were reported as the highest yet recorded for birds (Liknes and Swanson 1996).

Drinking, Pellet-Casting And Defecation

No information.