Nest Disturbance Research Articles

Egg burial depth by sockeye salmon (Oncorhynchus nerka): implications for survival of embryos and natural selection on female body size

We studied the relationship between female sockeye salmon (Oncorhynchus nerka) body size and egg burial depth in a small Alaskan stream to better understand the ways in which stream-bed scour or digging by other females might destroy embryos. Two different measurements of egg burial depth were taken: depth from the original stream-bed surface to the top of the egg pocket and depth from the disturbed substrate directly above the egg pocket to the top of the egg pocket. The former may represent the depth to which stream-bed scouring would have to go to reach the eggs, but the latter represents the depth to which a second female would have to dig to disturb the egg pocket. Larger females buried their eggs deeper, relative to the original substrate level, than smaller females. This suggests that streams with frequent scour events would select for larger females. However, mean depth from the disturbed substrate level was significantly shallower than mean depth from the original stream-bed level, suggesting that even the smallest females could dig deep enough to disturb the egg pockets of the largest females. Finally, the egg burial depth - fish size relationship that we observed was compared with published data on other salmonid species, revealing considerable variation but a clear positive relationship between female size and burial depth. Because embryonic survival is affected by scour and nest disturbance, and because changes in fish body size, density, and flow regime can affect the vulnerability of embryos to such mortality, we recommend further, standardized measurements of the relationship between egg burial depth and female body size.

Breeding of the Seychelles Magpie Robin Copsychus sechellarum and implications for its conservation

The total population of the Seychelles Magpie Robin Copsychus sechellarum declined from 38–41 birds in 12–13 territories in 1977–1978 to 17–21 birds in eight to nine territories in 1988–1990 and was entirely confined to Fregate Island (210 ha) in the Seychelles. After a successful cat eradication program in 1981–1982, recruitment improved, although the abandonment of agriculture had caused a reduction in the amount of feeding habitat and hence in the carrying capacity of the island. The population declined because of the failure of recruitment to compensate for the annual adult mortality. Foraging activity of the Magpie Robin was greater in high‐quality territories (measured by soil invertebrates available), leading to increased reproductive success. Through supplementary feeding, five times as many recruits were produced. Of the 11.5 potential annual breeding recruits, 5.3 are required to compensate for adult mortality, and the other 6.2 recruits can be regarded as “surplus” contributing to an increase. Magpie Robins prefer to breed in rotten trees, which are a scarce resource. The greater the distance between the nest site and feeding areas, the less time was spent in incubation and nest guarding, resulting in greater egg loss. Because of lack of suitable areas for establishing territories, many young Magpie Robins became “floaters”. Nest disturbance, both by these floaters and by the introduced Indian Mynah Acridotheres tristis, had adverse effects on the breeding success of robins. A recovery plan has been designed to save the Magpie Robin. Territories have been improved for feeding (by tree planting) and for breeding (by providing nestboxes and reducing nest disturbances). Given the vulnerability of one small island, the presence of surplus birds (supported mainly by supplementary food) and the suitability of neighbouring Aride Island (68 ha), successful translocations to this island took place in 1992 and 1994. Given the presence now of 47 individuals on two islands, it is hoped that the species will pull back from the brink of extinction.

Maternal care and differences in the use of nests in the domestic cat

Abstract. The domestic cat, Felis silvestris catus, exhibits several different forms of maternal behaviour, including solitary and communal care of offspring. Domestic cats, along with wild felid relatives, use covert nest sites in which to rear their young; multiple nest sites are used over the pre-weaning period. The presence of different maternal styles allows an examination of the functions of nest-moving. Two groups of semi-fetal cats, living in a large natural outdoor enclosure, were studied. Communal litters occupied twice as many nests as solitary litters over the first 6 weeks after birth. Kittens in communal litters also left the nest approximately 10 days earlier than kittens in solitary litters. After testing overall litter size with the number of nests occupied, the data showed little evidence that fouling of nests through an accumulation of elimination products, ectoparasites and food waste was responsible for increased moves. A more likely explanation is that frequent nest moves are employed to maintain nest covertness in the presence of possible predators and infanticide by conspecifics. Multiple carers may be better able to move nests efficiently and are therefore freed from the physical constraints affecting solitary mothers. Nest disturbance by several conspecific carers may be part of the explanation for nest moves, but probably does not account for the differences seen.

Central place foraging: a reappraisal of the ‘loading effect’

Animals that provision a central place usually bring back larger loads when foraging far from home. This positive correlation between average load size and distance is typically explained as rate-maximizing behaviour in the face of a trade-off between travel costs and a decelerating rate of prey gain in food patches (the ‘loading effect’). By using feeders to provide wild parent starlings, Sturnus vulgaris, with constant rates of prey loading, a positive load-distance correlation was shown to exist in the absence of a loading effect (experiment I). However, in a laboratory simulation where no load was transported (experiment II). the average number of prey eaten in patch visits by self-feeding starlings was invariant with travel distance, so the explanation of the load-distance correlation in experiment I must lie in featues peculiar to central place foraging. Bottlenecks in ingestion by chicks and interruption by visual detection of nest disturbance (experiment III) were rejected as causes of the correlation. Risks of dropping prey in flight appeared low, but the risk of kleptoparasitism received weak support. The travel-load size correlation may be an adaptive response to load transport costs, as return travel times increased with the load size being carried (experiment IV).

Conservation and management of the American crocodile

The American crocodile is a rare and endangered species, the range of which has contracted to disjunct locations such as Hispaniola, Jamaica, Cuba, Panama, and southern Florida. In an attempt to determine what factors might be limiting population growth, an extensive collaborative research program was conducted in 1978–82 in southern Florida. Limiting factors explicitly studied included climate, hurricanes, population dispersion, nesting habitat, fertility, predation, nest chamber environment, juvenile survivorship, artificial mortality, disturbance, and environmental contamination. No single natural factor limits the population, although in concert various factors result in low adult recruitment rates. Such natural limitations explain the natural rarity of this tropical species at the temperate limits of its range. Two artificial sources of mortality are death of adults on roads and the flooding of nests by high groundwater tables. These sources of mortality are potentially controllable by the appropriate management agencies. Active management, by such means as protection of individuals, habitat preservation and enhancement, nest site protection, and captive breeding, is also appropriate for assuring the survival of a rare species. The American crocodile has survived in southern Florida in face of extensive human occupancy of parts of its former nesting habitat, demonstrating the resilience of a threatened species. This case history illustrates the efficacy of conducting research aimed at testing specific management hypotheses, the importance of considering biographical constraints limiting population status in peripheral populations, the need for active management of rare species, and the role of multiple reserves in a conservation and management strategy.

Effects of Forest Fragmentation on Depredation of Artificial Nests

Depredation on artificial ground and arboreal (1.5 m above ground) nests was studied in mature (uncut) forest stands on a ruffed grouse (Bonasa umbellus) management area in central Pennsylvania from May to August 1986. Predation was evaluated in mature stands with zero, 25, and 50% zones of the surrounding forest fragmented by clearcutting. Nest depredation was highest in the 50% zone and least in the zero percent zone; more arboreal nests than ground nests were disturbed. American crows (Corvus brachyrhynchos) were major predators on nests in the 50% zone, and crows and blue jays (Cyanocitta cristata) caused most nest disturbances in the 25% zone. Our results suggest that fragmentation of surrounding mature forest stands may negatively impact avian nesting success, especially when the principal nest predators are corvids. Predation in fragmented forests may have a greater effect on nesting success of birds nesting above ground than on those nesting at ground level. J. WILDL. MANAGE. 52(1):158-161 Forest fragmentation, or the cutting of remaining natural forest into progressively smaller patches (Harris 1980), negatively impacts abundance and distribution of insectivorous passerines in the eastern United States (Whitcomb et al. 1981). Because forest fragmentation results in greater edge (Ranney et al. 1981) and predators select edges for foraging (Gates and Gysel 1978, Chasko and Gates 1982), predation on avian nests could increase with extensive forest fragmentation (Noss 1983). However, with the exception of a study dealing with predation on artificial nests in woodlots of various sizes (Wilcove 1985), the influence of forest fragmentation on nest predation is not well documented. Clearcutting forest to improve ruffed grouse habitat at the Barrens Grouse Habitat Management Study Area (BGMA) in central Pennsylvania provides suitable nesting habitat for a variety of avian species that nest ?2 m from the ground (Yahner 1986b, Yahner and Cypher 1987). The BGMA contains a sector with no forest fragmentation (zero clearcutting) and sectors with 2 intensities of forest fragmentation (25 and 50% clearcutting) that provided an opportunity to examine the relationship between nest depredation and forest fragmentation. Our objective was to compare depredation on artificial ground and arboreal nests placed in mature forest stands surrounded by uncut forest and 2 intensities of forest fragmentation at the BGMA. We thank R. A. Voytko and R. W. Bond for field assistance. Funding for this study was provided by the Max McGraw Wildlife Foundation and the Pennsylvania Agricultural Experiment Station. W. A. Creed, R. G. Eckstein, and M. J. Lacki reviewed the manuscript. This is Journal Series Paper 7565 of the Agricultural Experiment Station, The Pennsylvania State University, University Park.

The Effect of Shade and Competition on Emigration Rate in the Ant Aphaenogaster Rudis

Aphaenogaster rudis is a common ant in eastern United States forests that exhibits a high rate of colony relocation to new nest sites, even in the absence of nest disturbances. Field and laboratory experiments were conducted to determine if competition or reduced nest isolation, which acts to reduce internal nest temperature, could act as cues triggering colony emigrations. The field experiments tested the effect of increased food supply and artificial shade on the emigration rate. Laboratory experiments tested the effect of increased aggressive encounters with another ant species on emigration rate. Reduction in nest isolation resulted in a dramatic increase in the probability of emigration. Competition resulted in nest relocations only when it involved the invasion of the A. rudis nest site by another ant species. Changes in the amount of available food had no demonstrable effect on the probability of relocation although such changes did affect the intensity and direction of foraging activity. Seasonal trends in emigratory behavior were also observed. Emigration rate in A. rudis reached a maximum in midsummer. Also, the effect of artificially shading nests on emigration rate was the greatest in early summer and significantly less in spring and late summer.

Response to and transport of brood by workers of Tapinoma erraticum (Formicidae; Dolichoderinae) during nest disturbance

An attempt was made to describe the principle signals involved in the recognition of nymphs by Tapinoma workers. A behavioural measure, the way and extent to which workers transported different objects presented to them, was used to quantify this relationship. These objects were homo- or heterospecific nymphs, or different baits. Two types of test were generally used in such studies: retrieval — bringing back objects to the nest, and removal – transport of objects during displacement of the nest. The second type of test was used in this study. The results, in decreasing order of recognition were as follows. Tapinoma workers transport homospecific and Tetramorium nymphs at 100%. The smaller nymphs of Solenopsis impregnated with Tapinoma extract were transported at 77%. The nymphs of Solenopsis with their own odour were transported at 21%, paper impregnated. with Tapinoma extract at 12%, while ‘odourless’ Tapinoma nymphs and neutral paper were not transported at all. These results imply an intervention of both physical and chemical factors, the threshold significance of signals and their global implication depending on the test situation and its disturbing effect. They also depend on the nature of the different objects presented in combination; Tapinoma workers transport heterospecific brood much less readily in the presence of their own brood. The attractiveness of nymphs is not an all or none phenomenon. In a study of the adoption of homospecific nymphs from another nest, this gradation was apparent in the distribution of nymphs in the nest and their order of transport during removal tests; certain nymphs were left aside in the first 3 days of presentation, were amongst the last to be transported during removal, and then by the most active workers. The perception of the brood by the workers may thus occur at different levels: (1) Perception of a factor that may be vaguely defined as ‘transportable object’ in a removal test — with objects of type ‘nymph’ for example; (2) perception of the species; (3) perception of the colony. The worker ant during its life acquires a certain ‘knowledge’ of its own brood through familiarization, which expresses itself in terms of specific patterns of care for the brood, but this attention, although given preferentially to the brood, is not exclusive under stress.

Breeding Nests of Townsend's Mole in Oregon

Nesting habits of moles in Tillamook County, Oregon, were studied from March 1961 to June 1963. Breeding nests of 94 Townsend moles ( Scapanus townsendii ) and one coast mole ( Scapanus orarius ) that contained young were located and examined. Breeding nests were usually located in slightly elevated terrain and were indicated by a single large surface mound (30–50 inches in diameter) or a cluster of smaller mounds concentrated in a 6–10-ft area. Nest cavities were spherical, measured about 9 inches in diameter by 6 inches in depth and were 3–20 inches below ground level. Breeding nests had an inner core (25%) of fine dry grasses and an outer shell (75%) of coarse green grasses. Green grasses are added to the outer shell several times during the month the young occupy the nest. Following disturbance female moles frequently abandoned their nests prior to parturition but were more tolerant of nest disturbances after parturition. Trampling by dairy cattle was a common cause of nestling mortalities. Nestling young were classified into three age-groups based on external characters and size. Townsend moles weigh approximately 5 g at birth, develop rapidly and within 30 days are fully furred, weigh 60–80 g and are ready to abandon the natal nest.

THE ETHOLOGICAL ANALYSIS OF INCUBATION BEHAVIOUR

Summary.An integrative survey of behaviour mechanisms in birds, known to contribute to securing the proper conditions for the development of eggs during incubation, has been attempted. Our ideas of these mechanisms, schematically represented in Fig. 1, are mainly based on work with the Herring Gull, but, where possible, are compared with those on other birds.In addition to incubation (=sitting on eggs) several other activities of the fixed‐pattern type can be observed in a bird on its nest. Through statistical analysis of quantitative observations groups of these activities can be proved to have causal factors in common; consequently these groups are distinguished as separate systems (instincts). Different instincts which share common causal factors have been placed under the same superordinate instinct. A study of the biological significance of behaviour elements usually shows separate instincts to serve different functions. It should be stressed that distinguishing these instincts is of temporary value, helpful at this stage of the analysis as a shorthand description, but does not solve at all the problem of what exactly determines the grouping of behaviour elements. Inhibitive as well as stimulative relations between instincts have been found.Incubation, with the appetitive patterns of egg‐retrieving and settling, belongs to one system: the incubation instinct. It is argued that this system has inhibitive relations with the instincts serving preening, escape, and nest‐building, although with the latter it could also be shown to have causal factors in common.The degree to which the incubation instinct is activated depends—apart from other factors not mentioned here—on the weather and on the total value of the stimulus situation “nest with eggs in territory”. The latter situation seems to have a priming effect on the incubation instinct as well as a releasing effect on the activities egg‐retrieving and settling. The analysis of the mechanisms for evaluating this situation has been most thoroughly investigated for the releasing effect of the egg. In the Herring Gull this effect is the greater the more numerous, the smaller, the darker and the more contrasting the speckles are, the more the colour matches a light greenish tint and the greater the size of the egg. However, characters of shape are of hardly any importance. It seems likely that at least part of these “differential preferences” are due, not to the receptors, but to more centrally situated nervous mechanisms.Whereas an intact nest with eggs of high value mainly stimulates the incubation instinct, nest disturbances or eggs of low value also activate the tendency to leave the nest (escape instinct). This simultaneous activation of two conflicting tendencies is considered to cause an increase of preening and building, the rate between the frequencies of each depending on the relative strength of the tendencies.Reactions to disturbances at nest or clutch not only occur before the bird settles on the nest, but also during brooding. Incubation could be shown to continue effectively only when the proper feed‐back stimuli are received by the tactile‐ and thermo‐receptors of the brood patches; otherwise the appetitive activities of incubation set in, often mixed with (displacement) building and preening. Also under these circumstances building and preening are thought to arise in consequence of a conflict, as the abnormal tactile and temperature stimuli must stimulate the tendency to escape. Moreover, deviations of the egg temperature from normal lead to the performance of behaviour patterns serving the temperature regulation of the bird, which are also subordinate, together with the chemical heat‐regulation, to the thermo‐regulatory centre of the hypothalamus.