Main Foods Taken
Flying insects at all times of the year. Occasional pieces of seeds are found in stomachs (Beal 1918), but these represent either accidental ingestion or use as grit. Birds sometimes pick up small bits of gravel, probably to aid digestion of insect exoskeletons. A report of 2 birds with stomachs full of juniper (Juniperus) berries (Beal 1918) was likely based on misidentifications of Tree Swallows.
Microhabitat for Foraging
Feeds above the ground at altitudes of 50 m or more. Seems to prefer to feed over grassy pastures, plowed fields, and other open areas, but also feeds over floodplain forest, above canyons, and near towns. Forages over water (lakes, ponds, rivers) primarily when cool or rainy weather reduces insect availability and prevents formation of thermals that concentrate insects (Brown 1988, Brown and Brown 1996). Birds have been seen walking on the ground and picking ants off bare dirt in e. Washington (P. Stoddard pers. comm.) and brine flies off the shoreline at the Great Salt Lake, UT (Paton and Fellows 1994).
Food Capture and Consumption
Exclusively a diurnal forager, usually feeding in groups on aggregations of insects. In Nebraska, foraging groups during the breeding season vary from 2 to >1,000 birds, and some individuals feed solitarily. Birds often rely on local enhancement to discover insect swarms, watching nearby foragers and converging on a spot where the prey-capture behavior of other birds indicates a food source (Brown 1988, Brown and Brown 1996). While foraging, Nebraska birds use the Squeak Call (see Vocalizations) to signal when a food patch has been discovered. This call attracts other foragers and may serve to ensure that the insect swarm will be effectively tracked and that the discoverer can remain knowledgeable of its whereabouts (Brown et al. 1991). However, this call is used only in bad weather (poor foraging conditions) and relatively early in the season, and thus the contexts promoting calling are not well understood. The Squeak Call is used exclusively by birds on the foraging grounds and not at the colonies (Brown et al. 1991).
Foraging groups often feed on the lee side of bluffs or road cuts where insects concentrate (Brown 1988). Birds cue on thermals that passively transport insects aloft and on insect mating swarms and other types of aggregations (Brown and Brown 1996). Thermals and convection currents lead to a patchy distribution of insects, with the birds’ prey abundantly but unpredictably concentrated in several spots near a colony. When the air temperature is not warm enough for convection, birds feed lower over grass tops or water surfaces and in a more dispersed fashion (smaller groups). In cold weather, birds in Nebraska forage a few centimeters above the water and pick aquatic insects off the surface. Before nest-building starts, birds feed throughout the day in long bursts and may spend the entire afternoon away from the colony sites. After egg-laying begins, birds feed in more frequent and shorter bursts and are not absent from the colony for prolonged periods at any time of the day. After nestlings fledge, birds resort to longer foraging periods, like those early in the season.
While parents are feeding nestlings, Cliff Swallow colonies serve as information centers (Brown 1986). When a bird unsuccessful at finding food returns to its nest, it may watch its close neighbors; after a neighbor returns with food, the unsuccessful bird may follow that neighbor to a current food source when the neighbor next leaves the colony. Information transfer is unintentional; birds simply observe each other, with no evidence of active signaling at the colony to alert others that food has been found. However, Stoddard (1988) reported a tseer call used in rare circumstances by birds at colonies in Washington; the call seemed to signal that food was available. There is no evidence that birds try to disguise their foraging success to prevent others from following them (Brown 1986, Brown and Brown 1996). All birds alternate being followers and leaders, although how they discover insect swarms initially is unclear. Birds in small colonies (with few neighbors) do not wait at nests to monitor neighbors and instead spend that time searching for prey themselves. In huge colonies (≥1,000 nests), birds are less likely to monitor specific neighbors, and they often join the large groups that continually stream between the colony and food patches (Brown and Brown 1996).
Foraging in groups and using others to find food results in higher mean food intake rates for Cliff Swallows in groups than for birds feeding solitarily. Variance in prey-encounter rates is lowest for birds foraging in large groups (Brown 1988, Brown and Brown 1996). Consequently, birds nesting in larger colonies feed more efficiently and deliver more food to their offspring than do birds in small colonies. See Brown and Brown (1996) for a full discussion of how foraging efficiency is affected by colony size.
Nothing is known about feeding behavior on the winter range, but the large numbers of birds typically seen together (Hudson 1920, P. Burke pers. comm., V. Bowers pers. comm.) suggest that social foraging continues in winter and during migration.
Diet
Insects taken reflect local availability and may vary considerably among colonies located only a few kilometers apart (Brown and Brown 1996). The only generalization possible is that the birds prefer swarming taxa; 10 of the 15 most common families taken in Nebraska were ones known to swarm or otherwise aggregate (Brown and Brown 1996). A total of 84 insect families were represented in the diet of Nebraska birds, including homopterans, dipterans, hymenopterans, coleopterans, neuropterans, ephemeropterans, hemipterans, lepidopterans, orthopterans, and odonates. Grasshoppers are commonly taken during mid- to late summer when hot temperatures apparently reduce populations or activity levels of other taxa (Brown and Brown 1996). Insects not normally considered aerial are sometimes taken when they are transported aloft by thermals and convection currents. A Cliff Swallow colony can deplete the insect-pollinator population to the extent that it negatively affects seed-set of some plants near the colony site (Meehan et al. 2005).
In Nebraska, the most common family taken was Cicadellidae, followed in order by Dolichopodidae, Simuliidae, Formicidae, Empididae, Chironomidae, Muscidae, Culicidae, and Argidae (Brown and Brown 1996). In California (Beal 1907), families were not given, but the most common order was Hymenoptera (39% of total food), followed by Hemiptera (including Homoptera; 27%), Coleoptera (19%), and Diptera (12%). In a larger study of birds from unspecified parts of North America (Beal 1918), Hymenoptera again was the most frequent (28.7%), followed by Coleoptera (26.8%), Hemiptera–Homoptera (26.3%), and Diptera (13.9%).
Metabolism
Food-harvest rates of adults in California are estimated to be at least 3.40, 3.80, and 3.50 kcal/h during nest-building, incubation, and nestling periods, respectively (Withers 1977). Birds extend legs in flight to dissipate heat when ambient air temperature reaches 21–28°C (Butler 1982a) and gape and pant when hot.
Drinking
Birds drink exclusively on the wing by skimming water surface and lapping up water with lower mandible. Drinking is often done in groups, with many individuals suddenly starting and stopping simultaneously.
Flying insects at all times of the year. Occasional pieces of seeds are found in stomachs (Beal 1918), but these represent either accidental ingestion or use as grit. Birds sometimes pick up small bits of gravel, probably to aid digestion of insect exoskeletons. A report of 2 birds with stomachs full of juniper (Juniperus) berries (Beal 1918) was likely based on misidentifications of Tree Swallows.
Microhabitat for Foraging
Feeds above the ground at altitudes of 50 m or more. Seems to prefer to feed over grassy pastures, plowed fields, and other open areas, but also feeds over floodplain forest, above canyons, and near towns. Forages over water (lakes, ponds, rivers) primarily when cool or rainy weather reduces insect availability and prevents formation of thermals that concentrate insects (Brown 1988, Brown and Brown 1996). Birds have been seen walking on the ground and picking ants off bare dirt in e. Washington (P. Stoddard pers. comm.) and brine flies off the shoreline at the Great Salt Lake, UT (Paton and Fellows 1994).
Food Capture and Consumption
Exclusively a diurnal forager, usually feeding in groups on aggregations of insects. In Nebraska, foraging groups during the breeding season vary from 2 to >1,000 birds, and some individuals feed solitarily. Birds often rely on local enhancement to discover insect swarms, watching nearby foragers and converging on a spot where the prey-capture behavior of other birds indicates a food source (Brown 1988, Brown and Brown 1996). While foraging, Nebraska birds use the Squeak Call (see Vocalizations) to signal when a food patch has been discovered. This call attracts other foragers and may serve to ensure that the insect swarm will be effectively tracked and that the discoverer can remain knowledgeable of its whereabouts (Brown et al. 1991). However, this call is used only in bad weather (poor foraging conditions) and relatively early in the season, and thus the contexts promoting calling are not well understood. The Squeak Call is used exclusively by birds on the foraging grounds and not at the colonies (Brown et al. 1991).
Foraging groups often feed on the lee side of bluffs or road cuts where insects concentrate (Brown 1988). Birds cue on thermals that passively transport insects aloft and on insect mating swarms and other types of aggregations (Brown and Brown 1996). Thermals and convection currents lead to a patchy distribution of insects, with the birds’ prey abundantly but unpredictably concentrated in several spots near a colony. When the air temperature is not warm enough for convection, birds feed lower over grass tops or water surfaces and in a more dispersed fashion (smaller groups). In cold weather, birds in Nebraska forage a few centimeters above the water and pick aquatic insects off the surface. Before nest-building starts, birds feed throughout the day in long bursts and may spend the entire afternoon away from the colony sites. After egg-laying begins, birds feed in more frequent and shorter bursts and are not absent from the colony for prolonged periods at any time of the day. After nestlings fledge, birds resort to longer foraging periods, like those early in the season.
While parents are feeding nestlings, Cliff Swallow colonies serve as information centers (Brown 1986). When a bird unsuccessful at finding food returns to its nest, it may watch its close neighbors; after a neighbor returns with food, the unsuccessful bird may follow that neighbor to a current food source when the neighbor next leaves the colony. Information transfer is unintentional; birds simply observe each other, with no evidence of active signaling at the colony to alert others that food has been found. However, Stoddard (1988) reported a tseer call used in rare circumstances by birds at colonies in Washington; the call seemed to signal that food was available. There is no evidence that birds try to disguise their foraging success to prevent others from following them (Brown 1986, Brown and Brown 1996). All birds alternate being followers and leaders, although how they discover insect swarms initially is unclear. Birds in small colonies (with few neighbors) do not wait at nests to monitor neighbors and instead spend that time searching for prey themselves. In huge colonies (≥1,000 nests), birds are less likely to monitor specific neighbors, and they often join the large groups that continually stream between the colony and food patches (Brown and Brown 1996).
Foraging in groups and using others to find food results in higher mean food intake rates for Cliff Swallows in groups than for birds feeding solitarily. Variance in prey-encounter rates is lowest for birds foraging in large groups (Brown 1988, Brown and Brown 1996). Consequently, birds nesting in larger colonies feed more efficiently and deliver more food to their offspring than do birds in small colonies. See Brown and Brown (1996) for a full discussion of how foraging efficiency is affected by colony size.
Nothing is known about feeding behavior on the winter range, but the large numbers of birds typically seen together (Hudson 1920, P. Burke pers. comm., V. Bowers pers. comm.) suggest that social foraging continues in winter and during migration.
Diet
Insects taken reflect local availability and may vary considerably among colonies located only a few kilometers apart (Brown and Brown 1996). The only generalization possible is that the birds prefer swarming taxa; 10 of the 15 most common families taken in Nebraska were ones known to swarm or otherwise aggregate (Brown and Brown 1996). A total of 84 insect families were represented in the diet of Nebraska birds, including homopterans, dipterans, hymenopterans, coleopterans, neuropterans, ephemeropterans, hemipterans, lepidopterans, orthopterans, and odonates. Grasshoppers are commonly taken during mid- to late summer when hot temperatures apparently reduce populations or activity levels of other taxa (Brown and Brown 1996). Insects not normally considered aerial are sometimes taken when they are transported aloft by thermals and convection currents. A Cliff Swallow colony can deplete the insect-pollinator population to the extent that it negatively affects seed-set of some plants near the colony site (Meehan et al. 2005).
In Nebraska, the most common family taken was Cicadellidae, followed in order by Dolichopodidae, Simuliidae, Formicidae, Empididae, Chironomidae, Muscidae, Culicidae, and Argidae (Brown and Brown 1996). In California (Beal 1907), families were not given, but the most common order was Hymenoptera (39% of total food), followed by Hemiptera (including Homoptera; 27%), Coleoptera (19%), and Diptera (12%). In a larger study of birds from unspecified parts of North America (Beal 1918), Hymenoptera again was the most frequent (28.7%), followed by Coleoptera (26.8%), Hemiptera–Homoptera (26.3%), and Diptera (13.9%).
Metabolism
Food-harvest rates of adults in California are estimated to be at least 3.40, 3.80, and 3.50 kcal/h during nest-building, incubation, and nestling periods, respectively (Withers 1977). Birds extend legs in flight to dissipate heat when ambient air temperature reaches 21–28°C (Butler 1982a) and gape and pant when hot.
Drinking
Birds drink exclusively on the wing by skimming water surface and lapping up water with lower mandible. Drinking is often done in groups, with many individuals suddenly starting and stopping simultaneously.