Neighboring Nest Research Articles

Nest characteristics and breeding success of Black Kites (Milvus migrans migrans) in the High Plateau (Algeria)

The breeding ecology of the Black Kite Milvus migrans migrans in Algeria was first studied in 2014 and 2015 on Tarf Mountain in the semi-arid High Plateaus region. The nearest-neighbour nest distance was found to range from 130 to 550 m for colonial pairs and from 1,730 to 2,390 m for the solitary ones. All 12 monitored nests were placed on cliffs at different heights ranging from 149 to 155 m. The mean egg laying period was 15 days, and the mean clutch size was 2.83 ± 0.31 and 3 ± 00 eggs per nest in 2014 and 2015, respectively. The mean hatching success was 83% and that of fledging 75%. Only 2 nests were predated. Our results disagree with those of the previous studies that were carried out mainly in the Mediterranean basin and Asia, differing in such nest characteristics as the nearest - neighbour nest distance, cliff and nesting heights, egg laying period and hatching success. Otherwise, no consistent differences in clutch size and fledging success were revealed. Finally, we determined that Black Kites tend to build their nest on the eastern side of cliffs. However, our analysis showed no effect of nest placement on breeding parameters and success.

The presence of kleptoparasitic fledglings is associated with a reduced breeding success in the host family in the barn owl

Fledgling birds sometimes abandon their own nest and move to neighboring nests where they are fed by host parents. This behaviour, referred to as ‘nest‐switching’, is well known in precocial birds that are mobile soon after hatching and can easily reach foster nests. In contrast, due to the difficulty of observing nest‐switching in territorial altricial birds, the causes and consequences of moving to others’ nests are poorly known in this group of birds. Nest‐switchers can be adopted by the foster parents or they can steal food from the host parents meant for their offspring, a form of kleptoparasitism, which may result in reduced breeding success of the host nest. In Israel, 12 barn owl fledglings left their natal nests and were found in 9 host nests out of 111 monitored nests (8.1%). Nest‐switchers that fledged earlier in the breeding season flew shorter distances to reach host nests probably because the density of nests with younger nestlings is higher early in the season. The number of host nestlings fledged and the percentage of nestlings fledged was lower in host nests than in nests without switchers. The occasional nest‐switchers were always older than host nestlings (respectively 80 and 50 days of age, on average) and host parents fledged fewer young when nest‐switchers occupied host nests with younger nestlings. This suggests that nest‐switchers are kleptoparasites because the presence of the older alien fledglings is associated with a lower breeding success of the host parents.

Annual variation in distance to nearest neighbor nest decreases with population size in snowy plovers

Annual variation in distance to nearest neighbor nest decreases with population size in snowy plovers

Heterospecific Infanticidal Behavior by Southern House Wrens (Troglodytes aedon musculus) Suggests Nest Site Competition

ABSTRACT Destruction of conspecific and heterospecific eggs and nestlings occurs in several species of passerines. Two main hypotheses have been proposed to explain the adaptiveness of this behavior: as a mechanism to avoid competition or to gain access to reproductive opportunities. In Colombia, Southern House Wrens (Troglodytes aedon musculus) broke eggs and/or killed nestlings of Spectacled Parrotlets (Forpus conspicillatus, 24 cases), Apical Flycatcher (Myiarchis apicalis, one case) and of other House Wrens (four cases). Wrens attacked parrotlet nests in three contexts: 1) wrens took over and used a parrotlet nestbox within their territory, 2) wrens with an active nest attacked a neighboring parrotlet nest, or 3) the attacker was unknown but was inferred to be a wren. Wrens also attacked trial nests with natural and artificial wren eggs that were placed near active wren nests. These observations suggest that infanticidal behavior by wrens at this locality may be driven by competition for nest sites. I...

Intraspecific Adoption and Double Nest Switching in Peregrine Falcons (<i>Falco peregrinus</i>)

We describe an observation of post-fledging double nest switching and alloparenting in the Peregrine Falcon (Falco peregrinus tundrius). During the summer of 2010, a 36-day-old male Peregrine Falcon that had been marked with leg bands was seen flying from its natal site and was subsequently observed at a neighboring nest site that contained two nestlings. Motion-sensitive camera images indicated that the adopted nestling remained at the neighboring site for several days, during which time it shared the nest ledge with the two resident nestlings and was fed by the adults that occupied the site. The juvenile falcon subsequently returned to its natal site, where it shared the nest ledge with its natural sibling and received care from its natural parents. This note is the first documentation of nest switching in wild Peregrine Falcons.

41. Expansion of Ross’s gull nesting range in the north of Yakutia in the 20th century

The nesting sites of Ross’s gull – the North’s legendary bird, first discovered on the northern shores of Canada in 1823 and frequently encountered by Polar researchers in different areas of the Arctic Ocean from the Canadian shores and East-Siberian and Chukchi Seas, were first discovered in 1905 by S.A. Buturlin in the Kolyma River lower stream. Subsequent researchers identified the nesting range of this beautiful bird from the Yana River delta to the Lower Kolyma and Alazeya Rivers (Vorobyov, 1963). In the 1970–1980s the range of the species expanded further to the west. Ross’s gull nesting in the Lena River delta was registered in 1982, 1983, 1984, 1988, 1990 and 1994. Local inhabitants noticed Ross’s gull even farther westward on the Olenyok River and its tributary Bur River (Labutin et al., 1985). Pavlov and Dorogov (1976) write about the Ross’s gull propagation in Taimyr, in the Big Balakhnya River estuary. In early June 1994 we visited Sagystyr Island located in the Big Tumatskaya Channel estuary on the northernmost tip of the Lena River delta, where we found three solitary nests of Ross’s gull. The first two nests were made on a tussock among small lakes. They were made as cavities on the tussocks’ tops where soft moss was mixed with thinly laid dry grass and dwarf willow leaves. The third nest was arranged on the dry place near a geodesic tower and could be easily seen because of a white gull sitting in a neighboring nest and well outlined against the brownish tundra. When the bird left the nest, the nest seemed to disappear as it melted into the surroundings becoming absolutely unnoticeable. Each nest contained three well set eggs and the birds were sitting tightly. They flew up from the nest when a human came within 6–8 m, but they did not fly away and actively attacked the stranger. Ross’s gulls winter in the areas of the Arctic Ocean, the Okhotsk and Bering Seas of the Pacific Ocean. In the last decades the Ross’s gull population has grown considerably in number. However, it still needs human protection. It is necessary to conduct permanent monitoring of the population of this amazing endemic of the North and take all necessary protective measures.

Long-term familiarity promotes joining in neighbour nest defence

Familiarity plays an important role in the evolution of sociality and cooperation. Familiar individuals may gain a reputation for participating in, or defecting from, cooperative tasks. Previous research suggests that long-term familiarity with territorial neighbours benefits breeders. We tested the hypothesis that great tits (Parus major) are more likely to join in neighbours' nest defence if those neighbours are familiar from the previous year. We show that neighbours that shared a territory boundary the previous year are more likely to join their neighbours' nest defence than neighbours that did not share a boundary before. Closer neighbours did not differ from distant neighbours in their latency to join. For familiar neighbours that joined, there was no difference in call rate in relation to whether one or both members of the focal pair were familiar. First-time breeders (by definition unfamiliar) did not join each other's nest defence. This is the first evidence of a relationship between familiarity and joining in nest defence. Such direct benefits of familiarity may have important implications in the evolution of sociality.

Factors affecting individual variation in nest-defense intensity in colonially breeding Black-tailed Gulls (Larus crassirostris)

The physiological state of parent birds combined with the value of their clutch may affect the intensity of their nest defense. In colonially breeding birds, nest-defense intensity may also be affected by the behavior of neighbors. We investigated individual variation in the nest-defense intensity among colonial Black-tailed Gulls ( Larus crassirostris Vieillot, 1818) over 2 years. Only 30%–40% of males attacked a decoy of an egg predator (Large-billed Crow ( Corvus macrorhynchos Wagler, 1827)), and the other males and females rarely attacked. Males attacking the decoy had higher levels of plasma testosterone than males that did not attack. Each male’s, but not female’s, nest-defense intensity was consistent throughout the incubation period and also across years. The intensity was not related to egg-laying date, clutch size, or age of offspring. The intensity was likely to be higher when individuals had one or more neighbors, representing higher nest-defense intensity in the year where gulls had larger number of adjacent neighboring nests (5.23 nests), but this trend was not observed in the year where they had smaller number of the neighboring nests (3.73 nests). Thus, in addition to testosterone levels, behavior of neighbors also influences the nest-defense intensity.

CHIHUAHUAN RAVEN (CORVUS CRYPTOLEUCUS) REPRODUCTIVE SUCCESS AND NEST SPACING IN THE SOUTHERN HIGH PLAINS OF TEXAS

We measured reproductive success of 52 Chihuahuan raven (Corvus cryptoleucus) nests in the southern High Plains of Texas in 1999. Egg laying was initiated between 12 April and 21 June. We observed 5.2 ± 0.2 eggs (mean ± SE) per nest, 3.3 ± 0.3 hatched chicks per nest, and 2.6 ± 0.2 fledged chicks per nest. Incorporating “days at risk,” we estimated reproductive success was 36.5 ± 0.5%, and reproductive output was 1.9 fledged chicks per nesting female. Average distance from each nest to its nearest neighbor nest was 851 ± 168 m (minimum = 233 m, maximum = 8,465 m). Nest success was unrelated to nearest neighbor distance or nest height, but was correlated with clutch initiation date. The likelihood of nest failure increased by 0.9% with each passing day.

Nest odor dynamics in the social wasp Vespula vulgaris

We investigated nest odor dynamics in the common yellow jacket, Vespula vulgaris. In six isolated colonies, we tested the aggression rates toward dead nestmates that had been stored for 10 min, 10 and 19 days outside their colonies at -76 degrees C. The aggression rate increased from about 12% toward recently killed nestmates up to 30% toward nestmates killed 19 days before the experiment. Obviously, the conserved nest odor profile of the nestmates frozen for several days did not match with that of their colony anymore. This indicates a change of the nest odor within the colony. In a second experiment, we kept two colonies each in one nest box with a complete separation of both neighbor nests by a solid wall inside the box for 28 days. In confrontation experiments, the colony members treated dead foragers from the neighbor nest as aggressively as dead foreign, non-neighbor workers (about 39% each) whereas only about 14% reacted aggressively toward dead nestmates. Seventeen days after the replacement of the solid wall by a metallic grid, which allowed no physical contact but air exchange between the two neighbor colonies, the aggression rates toward foreign workers and nestmates remained relatively unaffected whereas it decreased significantly toward dead neighbors to about 11%. These results suggest a nest odor dynamic caused by volatiles transferred between two adjacent colonies, resulting in an equalization of the former colony specific nest odors. A change of nest odor dynamics influenced by volatiles was so far described only for one ant species at all.

Spatio-temporal patterns of colony distribution in monodomous and polydomous species of North African desert ants, genus Cataglyphis

Two monogynous species of North African desert ants belonging to the formicine genus Cataglyphis exhibit extremely different habitat preferences, population densities, and population structures. C. fortis is the only Cataglyphis species within the salt-pan flats of the Algerian and Tunisian chotts and sebkhas, whereas C. bicolor, alongside C. albicans and C. ruber, inhabits the nutritionally richer low-shrub semi-deserts surrounding the salt pans. We present a comparative study of the spatio-temporal patterns of colony distribution of the two monogynous species over periods of at least 5 (maximally 15) years. In C. fortis low population densities (0.5 kg body mass per km2) and, correspondingly, large inter-nest distances (40.6 m mean nearest neighbour nest distance) are correlated with absolute intra-annual and high inter-annual nest-site stability (more than 75% inter-annual survival rate) and a monodomous colony structure. In C. bicolor the population density is one hundred times higher (42 kg body mass per km2, 9.1 m mean nearest neighbour nest distance), nest-site stability is extremely low in both intra-annual and inter-annual terms (67% intra-annual survival rate for 13-day periods; less than 5% inter-annual survival rate), and polydomy prevails. These marked differences in population structure are discussed with respect to adapted traits such as foraging range, running speed, and relative lengths of the legs.

The Effect of Siblings on Nest Site Homing by Common Tern Chicks: A Benefit of Kin Recognition

-Studies of kin recognition in birds have rarely tested its adaptive value. We tested whether sibling recognition helps Common Tern (Sterna hirundo) chicks find their nests. The ability to discriminate the natal nest from neighboring nests is critical to survival in chicks of ground-nesting, colonial birds, such as the Common Tern. We temporarily moved 70 four-day old chicks 1 m from their nests and compared their ability to return home across the following treatments: siblings in natal nest, no chicks in nest, siblings in neighboring nest, and non-siblings in test chick's nest. With a sibling in the natal nest, test chicks returned within 20 min in 14 of 20 trials. In all other treatments, fewer than half of the chicks returned. When chicks did return, they typically did so within 5 min. Several additional factors may affect nest site homing, such as parental behavior, aggression by neighboring adults, and habitat type. To control for these factors, we restricted the dataset for analysis to 27 nests by excluding chicks led back to the nest by a parent, chicks attacked by neighboring adults, and nests on a rocky beach (most experiments were performed in grassy habitat). In the restricted dataset, seven of nine chicks with siblings in the nest returned. Two of five returned in the empty nest treatment, none of six with siblings at a neighboring nest returned, and one of seven with non-siblings in the nest returned. There was significant variation among treatments in the final distance of test chicks from their nests. Siblings appeared to affect nest site homing, even though parents usually returned quickly to the nest and were least likely to search for displaced chicks if siblings were home. We also tested the ability of singletons to return to the nest, using an identical protocol. Singletons returned to the nest in only two of 14 trials, in none of the six cases when the dataset was restricted. Received 15 September 2000, accepted 24January 2001.

Nest recognition in neighboring colonies: a comparison of two European species of Polistes wasps ( P. dominulus and P. nimphus , Hymenoptera: Vespidae)

The ability of two species of Polistes wasps to distinguish their own from nearby nests was tested, following the procedure used by Espelie et al. Our experiments demonstrated that, in the laboratory, females of Polistes dominulus and Polistes nimphus preferentially selected their own nests rather than nearby nests. We also evaluated the role of odor cues in nest recognition by washing nests in hexane to remove the apolar solvent-soluble components of nest odor. Although P. nimphus females continued to discriminate nests even after washing, P. dominulus individuals failed to discriminate between their own and a foreign neighboring nest. In both species, wasps were able to recognize their own nests when nest extracts were subsequently reapplied to the nest surface. These results indicate that P. dominulus wasps recognize their nests through perception of nest odor. The ability of P. nimphus wasps to distinguish their own nests even after presumed removal of the nest odor is discussed.

Relative reproductive success of female moorhens using conditional strategies of brood parasitism and parental care

In a population of moorhens (GaOinula chloropus), at least 27% of netting females laid one or more eggs in a neighbor's nest Females laid parasitically under three conditions: 56% of parasitic eggs were from nesting females that preceded laying a dutch in their own nest by a parasitic laying bout, 19% were from females whose nests were depredated before clutch completion and that laid the following egg parasiticaDy, and 25% were from a small number of females without territories, non-nesting parasites, that each laid a series of parasitic eggs. Clutch sizes varied greatly between females, but nesting females each laid a consistent clutch size both within and between seasons for a given mate and territory. Nesting females that employed a dual strategy of brood parasitism and parental care produced extra eggs that they laid in the nests of neighbors before laying a dutch in their own nests. Two out of ten females whose dutches I experimentally removed during the laying period were successfully induced to lay their next egg in the nest of a neighbor. Nesting females that laid parasitically selected their hosts opportunistically from among the nests dosest to their territories. An experiment in which parasitic eggs were removed and hosts left to rear only their own young showed that parasites did not choose hosts that were better parents than pairs with contemporary nests that were not parasitized. Females that only laid parasiticaDy within a given season timed their parasitic laying bouts poorly and achieved no reproductive success. Parasitic young rarely fledged, and the mean seasonal reproductive success of nesting brood parasites did not differ from that of nonparasitic females. However, the variance in reproductive success of nesting brood parasites was significantly higher than that of nonparasitic females.

Aggression and nest spacing in single and mixed species groups of seabirds.

When heterospecific seabirds are part of a nesting colony, there may be less opportunity for conspecifics to come in direct contact with each other, resulting in lower intraspecific aggressiveness. To determine if individuals spend less time in aggressive behavior when nesting in conspecific rather than heterospecific groups, we compared the behavior of black skimmers (Rhynchops niger) nesting with gull-billed terns (Sterna nilotica) in three mixed species subcolonies to those of black skimmers in three single species subcolonies. In contrast to our predictions, black skimmers spent significantly less time in aggressive behaviors when nesting in single species subcolonies than when nesting with heterospecifics. Although skimmers in mixed species subcolonies tended to have more aggressive interactions with skimmers than terns, this may be a function of subcolony composition; the proportions of aggressive interactions with conspecifics were similar to the proportions of conspecifics in each subcolony. However, within the mixed species subcolonies, skimmers that nested nearer to terns were involved in aggressive interactions significantly less than skimmers that nested closer to conspecifics. Also, skimmers nested closer to their nearest neighbor when it was a gull-billed tern than when it was another skimmer. Regardless of which species they nested closest to, skimmers were more aggressive towards other skimmers than to terns within the mixed species subcolonies. Distance to nearest neighbor's nest did not differ significantly between the colony types, and did not seem to influence the duration of aggressive activity in the single species subcolonies. In the mixed species subcolonies, however, the time spent in aggressive behavior increased as the distance to nearest neighbor increased. It appears that of the several benefits that have been proposed of mixed species colonies, reduced time spent in conspecific aggression is not among them. However, within a mixed species colony, an individual can reduce time spent in aggressive interactions by nesting near heterospecifics.

Fledgling Adoption in Hooded Warblers (Wilsonia citrina): Does Extrapair Paternity Play a Role?

Adoption is a widespread phenomenon in birds and generally occurs at a low frequency within a species (reviewed in Rohwer 1986, Meek and Robertson 1991). Adoption of fledglings is common in seabirds due to the mobility of chicks soon after hatch (e.g. Hebert 1988, Morris et al. 1991, Pierotti 1991, Brown et al. 1995). In songbirds, studies of adoption have focussed on the behavior of replacement males during the nestling stage (Meek and Robertson 1991). Little is known about fledgling adoption in songbirds because the fledgling period is poorly described for many species (Smith 1978, Moreno 1984). We report two cases of fledgling adoption in the Hooded Warbler (Wilsonia citrina) observed in the course of an intensive study of fledgling care (Evans Ogden 1994). In passerines, the main hypotheses for the adaptive significance of adoption by males are: (1) increased opportunities for fathering offspring with the offspring's mother in the future (Power 1975, Rohwer 1986); and, (2) as a result of extrapair matings, the adopting bird may be the genetic parent of the young it adopts (Meek and Robertson 1991). The first hypothesis is supported by comparative evidence that adoption tends to occur in species where females are likely to renest with the adoptive male (Rohwer 1986). Recent reports that extrapair fertilizations occur at high frequency in many Temperate Zone passerines (e.g. Westneat 1987, 1993, Morton et al. 1990, Stutchbury et al. 1994) indicate that the extrapair-paternity hypothesis for adoption may be more important than previously recognized. We used DNA fingerprinting of Hooded Warblers to examine whether extrapair paternity played a role in adoption. Our study was conducted from May through August 1991-1993 in Crawford Co., Pennsylvania (41?N, 79?W). The study site is a 150-ha continuous hardwood forest that supported about 40 breeding pairs of Hooded Warblers each year. Adults were captured with mist nets, banded with U.S. Fish and Wildlife aluminum bands, and individually color banded. Each brood member that fledged also was banded with an aluminum band, and all nestlings within a brood were given color-band combinations different from those of other broods. For most adults and nestlings, we collected 30 to 100 uL of blood for use in parentage analysis. Multilocus DNA fingerprinting (with Jeffrey's probe 33.16) was used to determine actual paternity of the adopted fledgling (for detailed methods, see Stutchbury et al. 1994). Unrelated adults had a band-sharing coefficient of 0.301 ? 0.017 (n = 22), so young were considered unrelated to their social father if they had a band-sharing coefficient of less than 0.42 and had more than two novel bands when compared with their social parents. Territories of color-banded males were mapped by following singing individuals and noting border disputes. The social father was the male that defended the territory at the time of egg laying and fed the young at nests on the territory. The social mother was the female that incubated the eggs and fed the young. Each year, we systematically attempted to locate family groups after fledging to determine the period of fledgling care and food-delivery rates to fledglings. In Hooded Warblers we rarely saw both parents feeding a given fledgling. Instead, the brood was usually divided and each parent assumed full care of one or two fledglings (Evans Ogden 1994). When the social mother attempted a second brood, the male assumed full care of all fledglings from the first brood. In the forested habitat, it was difficult to see young fledglings and determine color-band combinations to confirm the nest from which they fledged. To identify whether or not a parent had adopted fledglings, we used only those cases where adults were seen feeding color-banded fledglings on more than two occasions. Using these criteria, we observed fledgling care by 17 parents from 13 different families. Two of these 17 parents (12%) were observed to adopt young (i.e. they fed young on their own territory that had fledged from a neighbor's nest). Below we describe the two case histories in detail. The cases were similar in that the social father of the fledglings was no longer present on his territory at the time of adoption, and the social mother had renested to attempt a second brood. The second case was perhaps unnatural, because the social father died accidentally during handling early in the nestling stage. In the first case, a fledgling was fed by a neighboring male on the adjacent territory, beginning when the fledgling was 28 days old postfledging. At this time, the adoptive male was also feeding two of his own young (nine days postfledgling) on his territory.

Intraspecific competition through food robbing in the harvester ant,Messor aciculatus (Fr. Smith), and its consequences on colony survival

Intraspecific interference competition in the harvester ant,Messor aciculatus, was studied. Colonies of this species were found not to have territories. Some nests were located very close to each other, and the foraging areas of the neighbors usually overlapped. Even though the frequency with which alien and resident ants met was very high in the vicinity of the nest entrances, aggressive interactions between them rarely occurred. However, when hostile workers encountered each other, they exhibited a kind of ritualized combat and the winner ejected, but did not injure the loser. If any aliens entered the nest, some of them were pulled out, mainly by the residents. Aliens roaming near a neighbor's nest entrance ferociously attacked the residents carrying seeds in their mandibles and robbed them. On other occasions, aliens entered the nest and stole the collected seed. Although seed robbing and stealing occurred among neighboring colonies, there were remarkable differences in the frequency of their occurrence. The results of field observations and experiments suggest the existence of a dominance order among the neighbors. In one instance, extermination of an inferior colony by its neighbor was observed. The raider colony transferred the stored seeds from the nest of the inferior colony to its own and deposited the larvae and workers some distance away from the nest. The influence of ritualized combat and food robbing on colony activities, and the ecological significance of this interference behavior in terms of spatial distribution and temporal persistence of the nest sites, is discussed.

Ant Predation on Two Species of Birch Leaf-Mining Sawflies

-The impact of ant predation on two species of leaf-mining sawflies, Fenusa pusilla, which uses newly unfolding birch leaves, and Profenusa thomsoni, which uses older birch leaves, is examined. Ants prey upon F. pusilla larvae while they are still in their mines more often than they do on P. thomsoni larvae. The upper and lower epidermal layers of the mines of P. thomsonz are thicker than those of F. pusilla. Ant predation of F. pusilla larvae is related negatively to the density of birch saplings in the immediate vicinity of a mined leaf. Additionally, the presence of a neighboring ant nest appears to create a spatial refuge for F. pusilla in the area of overlap between the two nests.

Scanning electron microscopic observations of the basal surface of the human oral mucosa and squamous cell carcinoma

The basal surface of epithelial cells in the normal oral mucosa and cancer lesions were investigated by scanning electron microscopy. The basal lamina and collagen fibers having been completely removed by strong alkali digestion, the true basal surfaces of the epithelium and cancer lesions were demonstrated in three dimensions. Visible on the outer surface of the nest of cancer cells was a flowerlike structure, presumably the connecting portion of the neighboring cancer nest.

Intraspecific nest parasitism in the swallow Hirundo rustica: the importance of neighbors

Intraspecific nest parasitism in the swallow Hirundo rustica involves several parasite and anti-parasite tactics. Neighboring swallows breed asynchronously, perhaps because neighboring nests with overlapping egg-laying periods have higher frequency of intraspecific nest parasitims than neighboring nests with no such overlap. Since nest guarding prevents nest parasitism, the effect of nest guarding was removed by putting up old swallow nests. Such experimental nests were parasitized by swallows more often when the nests contained eggs, than when empty, and when the nests were far away from, rather than close to, an active neighboring nest. Close experimental nests with eggs were, however, parasitized less frequently if asynchronous (non-overlapping egg-laying periods), rather than synchronous, to active neighboring nests. Aggressive anti-parasite behavior of nest owners was determined from responses towards female intruders. Responses were more often aggressive before and especially during egg laying than during incubation. Nest owners also behaved aggressively more often when the intruder approached close to as compared to at some distance from their nest. Focal pairs behaved aggressively more often towards closely approaching intruders during the incubation period than towards distantly approaching intruders during the egg-laying period. Swallows reduce the frequency of intraspecific nest parasitism by nesting asynchronously with and close to a neighboring nest. Aggression by neighbors may reduce the success of potential parasitic swallows.