Condor, 81236~246 0 The Cooper Ornithological Society 1979 RESPONSES OF BARN SWALLOWS TO EGGS, YOUNG, NESTS, AND NEST SITES JOSEPH A. GRZYBOWSKI Aspects of egg, young, nest and nest site gentutus) nests moved about 30 cm were recognition have been investigated or ob- accepted if they contained eggs and the served in several species of birds (e.g., Cul- original nest site was covered with sand len 1957, Davies and Carrick 1962, Beer (Tinbergen 1953). In experiments with 1969, Peek et al. 1972). In general, selection Sooty Terns (Sternufuscutu), birds returned appears to favor recognition of as few char- to their nest sites rather than to nests dis- acteristics as necessary to insure a high placed short distances (Lashley 1915). From probability of caring for the correct eggs or these studies, it appears that selection fa- young. Birds that build nests respond to vors more rigid responses to changes in nest their nest sites, and later their young (usu- and nest site for colonial than for non-colo- ally when mobile), but show little evidence nial species. of specifically recognizing their own nests In the present study, I evaluated re- or eggs (Nice 1943, Tinbergen 1953, Beer sponses of Barn Swallows (Hirundo rustica) 1970). Common Murres (Uris aalge; John- to their eggs, young, nests, and nest sites. son 1941, Tschanz 1959), which do not Barn Swallows are facultative colonial nest- build nests, and Royal Terns (Sterna maxi- ers and unique among the above species in ma; Buckley and Buckley 1972), which nest that their colonies are passive aggregations in dense colonies where their eggs may be of birds (Snapp 1976). Barn Swallows have displaced, recognize both their eggs and recently used man-made structures for nest- laying sites. ing (Bent 1942), and such behavior may in- Among passerines, Rothstein (1975) found fluence the size of their aggregations. Do that some species (“rejector species”) can swallows respond to aspects of the nesting recognize foreign eggs placed in their nests, situation in the same way as colonial or non- while others (“acceptor species”) do not. colonial species? Bank Swallows (Riparia rip&a; Hoogland and Sherman 1976), Red-winged Blackbirds METHODS (Ageluius phoeniceus; Peek et al. 1972), and Carrion Crows (Corvus corone; Yom-Tov This study was conducted in southern and central Oklahoma during June and July of 1974, 1975 and 1976) do not discern their eggs, or their 1977. Swallow colonies were located in rectangular young until near fledging, at an age when cement culverts under heavy-duty roads. In 1974, two an “error” in progeny care is possible. Tri- culverts were used for the behavioral part of the study; colored Blackbirds (Ageluius tricolor), which one about 2.5 km southwest of Madill, Marshall County (left culvert in Fig. l), and one under State Highway nest in dense colonies, accept eggs or young 99 adjacent to Lake Texoma, Marshall County. The in- placed in their nests (Emlen 1941). Many side culvert dimensions were 183 cm (height) x 244 non-passerines are similar in their varied cm x 25.2 m (excluding triangular corner; see Fig. 1) ability to recognize their eggs or young and 213 cm x 152 cm x 48.0 m, respectively. In 1975 (Tinbergen 1953, Davies and Carrick 1962, and 1977, a culvert under State Highway 9 near Lake Thunderbird, Cleveland County, was used. It mea- Beer 1970). sured 183 cm x 183 cm x 49.6 m. Nests in culverts Red-winged Blackbirds recognize their were numbered sequentially, whether in use or not, nest sites specifically, but accept substitute and their locations described in relation to: (1) distance nests (Peek et al. 1972). Nero and Emlen from the entrance of culvert and/or nearest nest(s); and (2) shortest distance from outer lip of nest to ceiling of (1951) found that female Red-winged Black- culvert. birds would follow displaced nests even Mist nets were placed on the ends of the culverts, across territorial boundaries of males. Meise opened at night, and checked at sunrise. Captured (1933) moved the nest of a House Sparrow birds were banded and adults were marked with paint. (Passer domesticus) 1.5 m and observed no All males were marked conspicuously on the back with light blue. Females were painted so as to be individ- response to it by the adults. Among non-pas- ually recognizable by using a variety of colors (other serines, a Coopers’ Hawk (Accipiter coop- than light blue) on various parts of the body including erii) nest moved in small increments from left wing, right wing, back of neck, throat and rump. its original location in the crotch of a tall The paint did not appear to impair any individual, and paint-marked birds were captured in successive years. tree to a bushel basket, and then to the Sex was determined by measuring tail and wing chord ground, was accepted at each step by the lengths (Wood 1969), and by the presence or absence adults (Allen 1951). Herring Gull (Lurus ar- of a brood patch. 12361 BARN SWALLOW NESTING BEHAVIOR 237 ” .5 1.5 2.5 3.5 4.5 5,5 6.5 15 >8 METERS FIGURE 1. Nesting site of Barn Swallows in culverts FIGURE 2. Frequency distribution of distances be- under heavy-duty road near Madill, Marshall County, tween nests of Barn Swallows nesting in culverts (mea- Oklahoma. There were 17 active nests in culvert on sured to nearest cm). The white bars refer to distances left and 4 active nests in culvert on right. Note closed between all adjacent nest pairs (N = 137) while the mist-nets at entrance of culvert. shaded bars indicate distances between active nests (N = 84). I watched the birds, with the aid of 7 x 35 binocu- lars, from an automobile or burlap blind positioned the nest was 58 cm below the ceiling. The near the entrance of the culvert. A small mirror was mean distance between nests, for I37 adja- used to shine light into the culvert to confirm the iden- tity of birds sitting on nests. Marked birds were cent nest pairs in 11 culverts, was 2.79 m watched as they entered the culvert and went to their (SD = 2.27 m). Mean distances between 84 respective nests. After nests were identified with in- occupied nest pairs (i.e., nests with eggs or dividually-marked birds, I initiated the experiments. young) was 3.66 m (SD = 3.12 m). The latter Often, only the female using a particular nest was marked, but in no case did two birds identified as fe- represents a maximal value because young male use the same nest. may have recently fledged from “unoccu- Experimentation involved: (1) moving nests horizon- pied” nests located between the occupied tally or vertically from their original location; (2) add- ones. Frequency distributions, converted to ing nests; (3) removing nests; and (4) switching nests, proportion of total, were prepared for dis- and/or eggs and young. Nests to be moved were care- fully pried off the wall and reattached by laying down tances between nests of both data sets and an adhesive mud base to the new location and pressing are shown in Figure 2. With one exception, the moistened back of the nest onto the new location. the lowest distance between occupied nests Details of each manipulation are given in the results. was 0.73 m. Barn Swallows maintain some I observed the responses of Barn Swallows for at least 0.5 h after each manipulation. Observations were minimum distance between nests, but 60% extended up to 1.5 h in cases when the final response of the occupied nests were spaced less than was in doubt. The responses to nests (or nest sites) 3 m apart. were assigned to one of four categories: (1) no re- sponse-when a swallow appeared to ignore the nest RESPONSE TO EGGS (or nest site); (2) not accepted-when a swallow inves- tigated the nest (or nest site) by hovering in front of it, I evaluated whether or not Barn Swallows but did not land (occasionally, a swallow in this cate- are able to: discern their own eggs from oth- gory actually touched a nest, but did not perch); (3) er Barn Swallow eggs; distinguish Barn weak response-when a swallow attempted to incu- Swallow eggs from eggs of other species; bate or feed young (or perched at nest site), but re- jected these nests (or nest sites) during the observation and/or distinguish eggs from other objects. period (a swallow who sporadically fed young in a nest To test if females could distinguish their was placed in this category); and (4) accepted-when eggs from other Barn Swallow eggs, several a swallow continuously performed incubation or feed- manipulations were performed. When ing activities at a nest without apparent hesitation or clutches with identical numbers of eggs distress. Often, swallows in this category initially ex- hibited hesitation or distress when exposed to the ma- were substituted for the original eggs, fe- nipulated situation. males accepted the new set in all eight cases tested. In two of these, both the eggs RESULTS and nest were replaced. In two other in- In south-central Oklahoma, Barn Swallows stances, a females’ nest and eggs were re- placed their nests linearly on the wall just moved and replaced by two new nests im- below the ceiling of the culvert. The outer mediately ladjacent to the original location; lips of the nests were located 4 to 6 cm be- one of the nests contained her own eggs low the ceiling, except for one case where while the other included a clutch with the 238 JOSEPH A.