Food Habits

Feeding

Main Foods Taken

Winter: about 50% animal (mostly insects and spiders) and 50% plant (primarily seeds and berries).

Breeding season: 80–90% animal (largely caterpillars), the rest seeds and fruits (Smith 1991).

Microhabitat For Foraging

Winter: primarily arboreal, especially tree bark, from the main trunk to the thinnest twigs (including the underside of branches). Rarely on the ground.

Breeding season: similar to winter but expanded by addition of leaves. Exact location affected by other factors including weather (Grubb 1975, 1978) and relative rank of the individual (Glase 1973, Desrochers 1989).

Food Capture And Consumption

Robinson and Holmes (1982) described five foraging maneuvers of Black-capped Chickadees during the breeding season: (1) gleaning (taking food from the surface; 57% of total foraging time), (2) hanging (bird hangs from a leaf or twig, then picks food from surface; 28.7%; parids, including chickadees, have specialized leg muscles that aid in hanging from branches; Moreno 1990), (3) hovering (8.8%), (4) probing (3.5%) and (5) hawking (flying out and catching insects in mid-air; 2.4%).

Proportions of these maneuvers doubtless vary with season, year, and location. Sturman (1968) found individuals in Washington State spent significantly more time hanging in deciduous trees than in conifers. Relative rank and/or simple individual differences (Glase 1973, Heinrich and Collins 1983, Smith 1991) may also affect where and how a chickadee forages. Individuals feed only during daylight hours, but in winter may begin and end foraging at lower light levels than at other times of year, thus increasing foraging time during the shortest days (Kessel 1976).

During the breeding season, Black-capped Chickadees consume invertebrate prey that is quite cryptic. Heinrich and Collins (1983) found that chickadees use such cues as leaf damage (by caterpillars) and possibly even tree species in determining where to direct their foraging. Chickadees rarely eat food where they find it. More typically they carry it off to eat elsewhere. Two factors affect this behavior: food size (and thus handling time) and distance from cover (hence degree of exposure to predators). At any given distance from cover, the larger the food item, the more likely it will be carried away. When size is held constant, those food items closest to cover are those most likely to be carried off before being eaten (Lima 1985). Chickadees forage longer before giving up in trees with low prey density (Roche 1996) and prefer larger diameter trees in dry coniferous forests (Lyons et al. 2008).

Diet

Major Food Items

In the breeding season, caterpillars, particularly heterocampids, geometrids, and sphingids (Heinrich and Collins 1983); even some hairy caterpillars, such as early instar gypsy moths (Limantria dispar) and tent caterpillars (Malacosoma americanum; Bent 1946, Heinrich and Collins 1983, Smith 1991, Pelech and Hannon 1995). Also a wide variety of other insects, as well as spiders, small snails and slugs, and centipedes (Bent 1946); also berries, e.g., blackberries (Rubus sp.), honeysuckle (Lonicera sp.), and blueberries (Vaccinium sp.), as available. Black-capped Chickadees have been reported to eat the eggs of other bird species (Picman and Belles-Isles 1988, Pribil and Picman 1994, Maier and DeGraff 2000a,b).

In the nonbreeding season, animal matter is mostly insects and spiders, the former often in the form of eggs or pupae. Many reports of chickadees feeding on the fat of dead vertebrates, mammals such as deer (Odocoileus sp.; Glase 1973) or skunk (Mephites sp.; Hamerstrom 1942), and even fish (Southern 1966). Plant material includes weed seeds (e.g. goldenrod, Solidago sp., and ragweed, Ambrosia sp.), and seeds from conifers such as hemlocks (Tsuga sp.). Soft fruits such as blueberries, blackberries, wild cherries (Prunus sp.), tulip tree fruits (Liriodendron tulipifera) taken when available, and also small wax-covered berries like those of poison ivy (Rhus radicans) and bayberry (Myrica sp.).

Quantitative Analysis

In New York, overall, about 70% animal and 30% plant material (Bent 1946). Summer: about 80%–90% animal, 10%–20% plant. Winter: about 50%–50% animal-plant (Martin et al. 1951). In central British Columbia in fall: about 69% animal and 31% vegetable (Brodin 2005).

Nutrition And Energetics

No studies available on nutritional requirements. Parids the size of Black-capped Chickadees need approximately 10 kcal of energy/d (Smith 1991). Using doubly labeled water, Karasov et al. (1992) found that the daily energy expenditure of chickadees in winter in Wisconsin is 65.6 KJ day-1, which is about three times their basal metabolic rate. Seasonal changes in day length and food availability may influence fat deposition and metabolism (Karpouzos et al. 2005)

Metabolism And Temperature Regulation

Black-capped Chickadees do not increase mass in winter compared to summer (Cooper and Swanson 1994, Sharbaugh 2001). Fat stores increase seasonally but detection of differences in fat stores may depend on time of day (Chaplin 1974, Sharbaugh 2001; but see Linkes et al. 2005). Cooper and Swanson (1994) suggest that winter acclimatization is the result of metabolic changes. In winter, chickadees in South Dakota show increases in standard metabolic rate, maximal thermogenic capacity and cold tolerance compared to summer values. Chickadees also show increases in proteins associated with intracellular lipid transport in winter.

Rising and Hudson (1974) studied standard metabolism and thyroid activity in Black-capped Chickadees from Ithaca, NY, using birds held at several ambient temperatures. They found the standard metabolism of their chickadees in winter was 4.4 cm3O2(g–hr)-1 for birds maintained under natural conditions, and 3.6 cm3O2(g–hr)-1 for birds kept in the laboratory. The former value is 10% above, the latter 10% below, those calculated on the basis of body weight alone. This study also noted that the body temperature of roosting chickadees was labile, even in the summer. The former value is 10% above, the latter 10% below, those calculated on the basis of body weight alone. Standard metabolic rate of Alaskan chickadees is 15% higher than those in New York (Sharbaugh 2001).

Black-capped Chickadees from Vermillion, South Dakota, had standard metabolic rates of 3.54 cm³ O₂ (g–hr)^-1 in summer and 4.05 cm³ O₂ (g–hr)^-1 in winter (Cooper and Swanson 1994). Summit and basal metabolism of chickadees varies from winter to winter, and is higher during cold winters than during milder winters (Swanson and Olmstead 1999). Heavier chickadees have higher basal metabolic rates than lighter chickadees (Olson 2009).

Cold stress induces an increase in oxygen consumption which, in a laboratory-based study of winter-acclimatized birds, is the result of a slower breathing rate, an increase in volume of air inhaled (tidal volume), and an increase in oxygen extraction from the air (Cooper and Same 2000). This effect is not observed until birds reach 50% of their maximal metabolic rate (Cooper and Blewett 2001). Compared to winter-acclimatized birds, summer-acclimatized birds exposed to the same conditions increased oxygen consumption only by increasing tidal volume. The level of oxygen extraction recorded by Black-capped Chickadees can enter a state of regulated hypothermia on cold winter nights. By dropping their body temperature, typically to 10°–12°C below their ordinary daytime body temperature, they save significant overnight energy expenditure (Chaplin 1974, 1976). Chickadees in Alaska, where summer temperatures may fall below freezing, maintain the ability to enter nocturnal hypothermia in summer (Sharbaugh 2001). Smith (1991) provides further discussion of winter energetics in chickadees. Report of thermogenic (heat-producing) brown fat in this species (Oliphant 1983) has not been confirmed (Olson et al. 1988). Heat produced by muscular activity when foraging can substitute for thermoregulatory requirements in cold weather. Body temperature of perching and foraging chickadees did not differ (Cooper and Sonsthagen 2007).

Drinking, Pellet-Casting, And Defecation

In winter, may obtain much of their fluid requirements from food, although they drink readily if water is available (e.g. from melting icicles); also eat snow (Bent 1946). Greatest need for water is at high temperatures, when excess heat may need to be dissipated by evaporative cooling (Rising and Hudson 1974).

Captive birds will cast pellets, e.g., beetle wing casings mixed with the outer coats of berries (SMS); wild birds presumably do likewise. Typically defecate several times/h during the day; little known about nocturnal defecation rates. Fecal pellets of nestlings typically covered with a gelatinous coat that facilitates removal from the nest cavity.

Food Selection And Storage

See Lima (1985), Barkan and Withiam (1989), Barkan (1990), and Smith (1991) for discussions of optimal foraging in this species.

Like many other parids, these chickadees cache food, mostly seeds but also insects (Heinrich and Collins 1983). Chickadees in central British Columbia cache 64% seeds and berries and 33% insects (Brodin 2005). Most caching done in autumn, but individuals cache throughout the year (Odum 1942, Brodin 2005). Common caching sites include bark, dead leaves, lichens, clusters of conifer needles, knotholes, and even dirt or snow (Odum 1942, Haftorn 1974, Petit et al. 1989). Caching may be important in overwinter survival, especially in high latitude populations. Caching chickadees may carry off several items (e.g., sunflower seeds) at a time, but each item is stored in a separate location. Chickadees avoid caching food close to forest edges (Brotons et al. 2001).

Sherry (1984, 1989) has shown that individuals can find cache sites accurately 24 h after storage; Hitchcock and Sherry (1990) documented accurate cache recovery after 28 d. Dominants cache more than subordinates (Hitchcock and Sherry 1995), but there are no sex differences in food-caching or memory for cache location (Petersen and Sherry 1996). Chickadees may use a combination of cues including sun compass orientation and landmark information when recovering caches (Duff et al. 1998). Chickadees also remember which sites have been emptied, both by themselves and by others, and they remember the relative quality of cached items, spending more time searching at sites where higher energy content items were stored (Sherry 1984).

A potential pilferer that watches another chickadee cache a seed is not significantly more likely to find that seed (Baker et al. 1988), although the presence of other chickadees evidently lowers a chickadee’s likelihood of storing seeds (Stone and Baker 1989, Baker et al. 1990). Only a small percentage of cached seeds are likely to be pilfered (Hitchcock and Sherry 1995). For a detailed review of caching behavior of Parids see Sherry and Hoshooley (2007).

Sherry et al. (1989) found that the hippocampus (the brain region associated with spatial memory; see Shiflett et al. 2003) is proportionately larger in chickadees and other parids than in families that do not cache food. Within the Paridae, the Black-capped Chickadee hippocampus is proportionately larger than in related species that cache less food (Hampton et al. 1995, Lucas et al. 2004), as is the septum (Shiflett et al. 2002). Hippocampal volume (Smulders et al. 1995, 2000; but see Hoshooley et al. 2007), and neuronal recruitment (Barnea and Nottenbohm 1994, Hoshooley and Sherry 2004) are greater in chickadees in autumn when caching occurs than at other times of year. There are no sex differences in hippocampus size (Petersen and Sherry 1996). Chickadees in harsher Northern climates have larger hippocampi with more neurons than do chickadees at milder southern latitudes (Roth and Pravosudov 2009). Alaskan chickadees cache at higher rates and have larger hippocampal volumes than do chickadees at lower latitude in Colorado (Pravosudov and Clayton 2002), but do not have larger baseline corticosterone levels (Pravosudov et al. 2004). For a detailed review of food caching, spatial memory, and the hippocampus, see Pravosudov (2007).