How well do predation rates on artificial nests estimate predation on natural passerine nests?

Daily survival rates (DSR) of three nest types were compared among three passerine species in woodland habitats of the Czech Republic in 1998‐99. The species were: Yellowhammer (YH) Emberiza citrinella, Blackcap (BC) Sylvia atricapilla, Song Thrush (ST) Turdus philomelos. The nest types were: AA, artificial nests with artificial plastic eggs, both mimicking the real models (total n= 432); NA, natural nests left in their original position and baited with artificial plastic eggs (n= 706); and NN, active natural nests observed during the egg stage (n= 596). Rodents were dominant predators of the near‐ground YH nests while predation by corvids slightly prevailed in the shrub nests of BC and ST. There was no consistent relationship between nest type (AA vs. NA) and type of predator. Effects of nest type (AA vs. NA or AA vs. NN, respectively), species, date and study plot on DSR were examined by fitting logistic regression models. Marginally significant (< P < 0.05) differences were found between AA and NA nests in both years. Due to the interaction with date in 1998, the model predicted lower/higher DSR for AA nests before/after about 25 May respectively. In 1999 the DSR of AA nests was consistently higher (difference: 0.011; 95% CI: 0.001 to 0.021). Marginally significant differences between AA and NN nests were found only in 1998: the DSR of AA nests was consistently lower (‐0.014, 95% CI: ‐0.027 to ‐0.001). Comparisons of mean DSR within each species‐year sample showed that the differences between nest types were of both directions and varied from almost zero to 0.02 (ST, BC; ns) or 0.04 (YH; P < 0.05). Although the experimental nests accurately reflected the mean values as well as seasonal trends and interspecific differences in DSR of the real nests in some subsets of data, the pattern was not consistent across species and between years. This study suggests that artificial nests could not be used to assess survival of natural nests without careful validation of the experimental results.     

Do chimpanzees build comfortable nests?

Nests built by wild chimpanzees (Pan troglodytes verus) were studied at the Fongoli research site in southeastern Senegal from January 2004-May 2004 to investigate the role of comfort in nest building behavior by relating measures of nest comfort and building effort. Nest comfort across zones of the nest surface were compared with construction effort for 25 nests. Several variables of nest comfort were assessed: (1) physical discomfort, (2) visible discomfort, and (3) softness. Physical discomfort was used as a representative measure of nest discomfort. Building effort was measured by (1) construction force, (2) complexity, and (3) added material. Spearman rank correlations compared Effort and Comfort measures for both whole nests and central versus edge zones. The results show that construction force and complexity do not influence comfort of the nest as a whole. Greater Construction force correlates with more nest edge discomfort, yet the central area shows no difference. More complex nests do result in a more comfortable central area in the nest. Nests built with greater force may result in more discomfort, whereas complexity may allow chimpanzees to maintain comfort in a central area for sleep. Chimpanzees may place additional leaves or twigs over hard branches, protruding from the nest surface after construction, to increase comfort of the central nest area. Functions of chimpanzee nest building are likely to be several, but these results suggest comfort is a factor in nest building behavior.     

How do goannas find sea turtle nests?

Squamate reptiles rely heavily on visual and chemical cues to detect their prey, so we expected yellow‐spotted goannas (Varanus panoptes) which are predators of sea turtle nests on mainland beaches in northern Australia would use these cues to find sea turtle nests. Ghost crabs (Ocypode ceratophthalmus and Ocypode cordimanus) are also common on Australian sea turtle nesting beaches and frequently burrow into sea turtle nests. However, the potential for ghost crab burrowing activity at sea turtle nests to signal the location of a nest to goannas has not been investigated. Here, we used camera traps and presence of tracks at nests to record goanna activity around selected nests during the incubation period and 10 days after hatchling turtles emerged from their nests. We also recorded the number of ghost crab burrows around nests to evaluate ghost crab activity. Our results indicated that nest discovery by goannas was independent of nest age, but that the nest visitation rate of goannas and crabs increased significantly after a nest had been opened by a goanna or after hatchlings had emerged from the nest. There was no apparent connection between ghost crab burrows into a nest and the likelihood of that nest being predated by goannas.     

Can birds count eggs in their nests?

Sensory mechanisms controlling avian clutch size have diversified into distinct types, according to the nature of the input that is used to disrupt the growth of ovarian follicles and hence halt egg‐laying. In an article on brood parasitism, Lyon (2003) claimed that female American Coots Fulica americana can reduce their clutch size on the basis of visual cues in response to eggs laid in their nests by other females; in this species, therefore, egg counting would be used to control clutch size. After a close examination of the physiological determination of clutch size in American Coots, I show that seven of 17 parasitized clutches were smaller than the range controlled through the mechanism using an input to disrupt follicular growth (7–10 eggs per clutch). My reanalysis suggests that American Coots are incapable of adjusting clutch size via counting and re‐asserts that a species that can count eggs has yet to be found among birds that rely upon their own body heat for incubation.     

Does human scent bias the survival of bird nests?

Human-scent contamination of bird nests and the human-made trails leading to them is suspected to influence nest survival by attracting or deterring predatory mammals. This paper (1) reviews studies in which human-scent contamination was suspected to have biased the survival of real and artificial nests by influencing the behaviour of predatory mammals, (2) summarizes the procedures used in attempts to mitigate human-scent contamination in nest-survival studies, and (3) describes procedures to enhance the design and interpretation of nest-survival experiments. The behaviour of various non-domesticated mammals is confirmed or suspected to be affected by human scent, so similar effects on nest predators are plausible. However, suggestions that human scent affects nest survival by influencing the behaviour of predatory mammals are poorly supported, due to a dearth of appropriately designed experiments. Some studies failed to include measures to reduce human-scent contamination, and the effectiveness of scent-mitigation methods used in other studies has seldom been verified. In addition, volatile compounds arising from soil and vegetation disturbed underfoot by field researchers may have confounded many nest-survival studies. Investigators have routinely inferred human-scent effects from post hoc predation patterns or have simply acknowledged possible human-scent effects among other potential influences of nest fate. Studies are needed of the effects of human scent using uniform methods of scent application and verified methods of scent mitigation, where the fates of different types of nests are examined under a range of field conditions. More fundamentally, studies of naïve and experienced mammals are needed to assess their responses to human scent and clarify its salience in wildlife disturbance.     

Does land use change influence predation of bird nests?

Worldwide, many areas of agricultural land which were once covered with native vegetation have been converted to tree plantations. Such landscape transformation can influence the dynamics of wildlife populations through, for example, altering rates of predation (e.g. predation of nests of birds). Nest predation can influence reproductive success and, in turn, may alter populations by affecting juvenile recruitment. We quantified predation of bird nests in woodland remnants surrounded by two types of land use, grazing farmland and exotic Radiata pine (Pinus radiata) plantation. We also examined differences in predation rates between artificial and natural nests. We found both artificial and natural nests were more susceptible to nest predation in woodland remnants surrounded by a pine plantation than in woodland remnants located within farmland. Our study suggests that higher levels of nest predation may reduce occupancy of woodland remnants by small‐bodied birds over time, including species of conservation concern. This may have been occurred as a result of the conversion of semi‐cleared grazing land to exotic pine plantation.     

Does cooperation mean kinship between spatially discrete ant nests?

Eusociality is one of the most complex forms of social organization, characterized by cooperative and reproductive units termed colonies. Altruistic behavior of workers within colonies is explained by inclusive fitness, with indirect fitness benefits accrued by helping kin. Members of a social insect colony are expected to be more closely related to one another than they are to other conspecifics. In many social insects, the colony can extend to multiple socially connected but spatially separate nests (polydomy). Social connections, such as trails between nests, promote cooperation and resource exchange, and we predict that workers from socially connected nests will have higher internest relatedness than those from socially unconnected, and noncooperating, nests. We measure social connections, resource exchange, and internest genetic relatedness in the polydomous wood ant Formica lugubris to test whether (1) socially connected but spatially separate nests cooperate, and (2) high internest relatedness is the underlying driver of this cooperation. Our results show that socially connected nests exhibit movement of workers and resources, which suggests they do cooperate, whereas unconnected nests do not. However, we find no difference in internest genetic relatedness between socially connected and unconnected nest pairs, both show high kinship. Our results suggest that neighboring pairs of connected nests show a social and cooperative distinction, but no genetic distinction. We hypothesize that the loss of a social connection may initiate ecological divergence within colonies. Genetic divergence between neighboring nests may build up only later, as a consequence rather than a cause of colony separation.     

Does weather affect biting fly abundance in avian nests?

Environmental factors may strongly affect avian‐biting fly interactions in different ways because insects are heterothermic organisms that depend greatly on environmental variables to activate their metabolism and behaviour. We studied the effects of weather on both blackfly (Simuliidae) and biting midge Culicoides (Ceratopogonidae) abundance in nests of three passerine species: blue tits Cyanistes caeruleus, great tits Parus major and pied flycatchers Ficedula hypoleuca, breeding in the same area. We controlled for different host‐related factors (hatching date, brood size and host species). Blackfly abundance was negatively related to minimum temperature. In addition, blackfly and biting midge abundances were negatively affected by wind speed measured at 07.00 h, but blackfly abundance was positively associated to wind speed at 18.00 h. We found higher blackfly and biting midge abundances in nests with larger broods breeding later in the season, and significantly higher biting midge abundance in pied flycatcher nests as compared to tit nests. These results represent, to our knowledge, the first report of both environmental and host‐related effects on haematophagous fly abundance in the nests of wild hole‐nesting birds.     

Does cowbird parasitism increase predation risk to American redstart nests?

Brood parasitism and nest predation are major causes of reproductive failure for many bird species nesting in fragmented landscapes. While brood parasites and predators may act independently, they could also interact if brood parasites increase the likelihood that predators detect nests. In this study, we examined the interaction between cowbird parasitism and nest predation in a 10 year study on 466 American redstart Setophaga ruticilla nests in central Alberta, Canada. We used advanced nest survival models to examine the support for three mechanisms that might lead to a positive correlation between brood parasitism and nest predation: 1) the presence of a cowbird nestling might increase the detection of the nest by predators, 2) nests with lower cover are more likely to be detected by both cowbirds and predators, and 3) cowbirds and predators may co-occur in landscapes of similar structure. Twelve percent of nests were parasitized and those nests had a 16–19% higher rate of failure due to predators compared to unparasitized nests. Daily nest predation rates increased during the nestling stage for both groups, but more strongly for parasitized nests. Loud begging by the cowbird nestling and/or higher parental feeding rates for the cowbird may have increased nest detectability to predators. Brood parasitism and nest predation were also positively related to forest cover, indicating landscape level effects were influential. Most nest predators were forest species and we suspect cowbirds responded positively to forest cover because of the increased abundance of songbird hosts. Nest-site features had less of an impact on nest predation or brood parasitism, although nests with higher overhead cover were less susceptible to predators. Our study shows how multiple mechanisms, particularly the behavioral effects of the brood parasite nestling and landscape structure, can lead to a positive relationship between nest predation and brood parasitism.     

Why do female lizards lay their eggs in communal nests?

1. In many reptile species, females oviposit communally (i.e. many clutches are laid within the same nest). This behaviour might result from constraint (scarcity of nest-sites offering suitable incubation conditions) or adaptation (direct fitness benefits accruing from the proximity of other eggs). 2. To test between these alternatives, we gathered field and laboratory data on montane scincid lizards Bassiana duperreyi from south-eastern Australia. Our data support the adaptationist hypothesis. 3. In the field, communal vs. solitary clutches were laid in similar sites, and the relative frequency of communal nesting was not predictable from nest-site availability. Thermal regimes for incubation did not differ between communal vs. solitary nests, nor between eggs at the core vs. periphery of a communal nest. In the laboratory, females selectively oviposited beside existing eggs rather than in otherwise identical potential nesting sites. 4. From cycling-temperature incubation in the laboratory, eggs incubated within a cluster of other eggs took up less water, but produced hatchlings that were larger and faster-running than were hatchlings from eggs incubated alone. 5. Hydric modifications of incubation conditions within a cluster of tightly packed eggs thus may provide a direct fitness benefit to communal oviposition.     

Odour cues from suitors’ nests determine mating success in a fish

Animals use a range of sensory cues for finding food, avoiding predators and choosing mates. In this regard, the aquatic environment is particularly suitable for the use of olfactory and other chemical cues. Nevertheless, mate choice research, even on aquatic organisms, has focused on visual signals, while chemical cues relevant in sexual selection have been assumed to be ‘intrinsic’ excretions of mate candidates. Here, using the sand goby Pomatoschistus minutus, a small fish with paternal egg care, we investigated the possibility that ‘extrinsic’ chemical cues in the males’ nests could also have a significant contribution to mating success. We found that females strongly avoided laying eggs into nests subject to the odour of Saprolegnia water moulds (an egg infection) and that this effect was independent of the females’ initial, visually based preference for males. To the best of our knowledge, this is the first study to show that chemical cues related to parental failure can play a large role in sexual selection.     

Aromatic herbs in Corsican blue tit nests: The ‘Potpourri’ hypothesis

This study reports that Corsican blue tit (Parus caeruleus ogliastrae) nests contain between one to five aromatic herb species between the onset of egg laying till the chicks’ finished growth 13 d after hatching. An herb removal experiment during the chick stage shows that blue tits bring fresh aromatic material 1–5 d after herb removal. Nests with a series of distinct odour classes easily perceived by humans have never been reported in birds. A new ‘Potpourri’ hypothesis is proposed that may explain the functional significance of this behaviour.     

Occurrence of the medicinal leech (Hirudo medicinalis) in birds’ nests

Occurrence and breeding of Hirudo medicinalis were recorded in birds’ nests in the fishing ponds and water bodies used extensively by anglers in south-eastern Poland, in 4 of 11 studied bird species (Circus aeruginosus, Fulica atra, Cygnus olor, Chroicocephalus ridibundus). Factors important for the distribution and density of this leech were: nest height, pH of the water and oxygen concentration in the water inside the nests, the body-length of the nesting birds. Our data show that (1) H. medicinalis chooses nests as habitats that are safe in water bodies rich in predators (particularly fish) and provide stable feeding conditions; (2) fishing ponds and other water bodies used extensively by anglers in a landscape modified by human pressure can be an important secondary habitat for the medicinal leech. As the nesting activity of some aquatic birds apparently favors the occurrence of H. medicinalis, active protection of aquatic birds and creating sites appropriate for their breeding may be an indirect way for the conservation of the leech in such areas.     

Do bright colors at nests incur a cost due to predation?

Summary Birds show much interspecific variation in the coloration and brightness of their plumage. I examine the hypothesis that selection due to predation on incubating birds and their nest contents can explain part of this diversity. First, I argue that rather than using absolute rates of nest predation to make predictions about the costs of conspicuous colours, we should measure experimentally whether increases in plumage conspicuousness elevate rates of nest predation. Second, I present experimental data investigating the cost of red and brown colour at ground and tree nests. These data provide the first evidence that bright colours do attract predators to nests and that, in addition, this cost varies according to the nesting site. Natural selection seems to most strongly oppose the evolution of conspicuous colours in ground-nesting birds.     

Does competition for nests affect genetic monogamy in Cory's shearwater Calonectris diomedea?

Most bird species are socially monogamous. However, extra‐pair copulations (EPCs), resulting in extra‐pair paternity (EPP), commonly occur. EPCs should allow females to adjust social mate choice and allow males that fail to obtain a nest a chance to avoid missing a breeding season, especially when poor nest supply constrains social mate choice. Procellariiformes (albatrosses and petrels) are socially monogamous seabirds which seldom divorce, even when nest availability constrains social mate choice. In Cory's shearwater Calonectris diomedea, a burrow‐nesting petrel, two studies conducted in the Mediterranean, where competition for nests is weak, detected no EPP. EPP remains to be investigated at localities where competition for nests is much stronger, such as Vila islet, Azores archipelago, Atlantic Ocean. We conducted a genetic (microsatellites) study over two successive years on Vila, involving the breeding pairs of the same 65 nests each year and their single chick. EPPs occurred each year, the overall rate being 11.6%. Coupling genetic analyses to a 7‐year demographic survey provided additional data on pair bonds and competition for nests. Overall, cuckoldry was unrelated to divorce, nest density and inbreeding avoidance, but was more frequent when the social male was small. Nest changes were more costly for males than for females, and some apparently unpaired males attempted to dislodge social males during within‐pair copulations. These results are compatible with the existence of a link between poor nest availability and EPP and confirm that even species considered strongly monogamous can adopt flexible mating strategies.     

When should Common Cuckoos Cuculus canorus lay their eggs in host nests?

Capsule Brood parasitic Common Cuckoo Cuculus canorus chicks hatch earlier than the nestlings of their Great Reed Warbler Acrocephalus arundinaceus hosts, but hatching priority is less consistent when Cuckoo eggs are laid after the onset of host incubation.

Aim To reveal by field observations what the optimal stage is for Cuckoos to lay their eggs in relation to the host laying cycle to ensure prior hatching of the parasitic chicks.

Methods We monitored the hatching of Cuckoo chicks in relation to the hosts’ laying stage at which the Cuckoo eggs appeared and also monitored host incubation behaviour.

Results Great Reed Warblers incubated more on day 5 after the host's onset of laying relative to day 3. All Cuckoo eggs hatched earlier than hosts when they were laid prior to the onset of host incubation (day 4). Cuckoo eggs also maintained hatching priority in about 2/3 of the nests when laid on days 5–6.

Conclusions Most Cuckoo eggs are laid prior to the onset of host incubation and this, together with other adaptive mechanisms, ensures the prior hatching of Cuckoo eggs. Cuckoo eggs laid after the onset of incubation lose the advantage of prior hatching in approximately 30% of nests.     

Alien eggs in duck nests: brood parasitism or a help from Grandma?

Intraspecific brood parasitism (IBP) is a remarkable phenomenon by which parasitic females can increase their reproductive output by laying eggs in conspecific females' nests in addition to incubating eggs in their own nest. Kin selection could explain the tolerance, or even the selective advantage, of IBP, but different models of IBP based on game theory yield contradicting predictions. Our analyses of seven polymorphic autosomal microsatellites in two eider duck colonies indicate that relatedness between host and parasitizing females is significantly higher than the background relatedness within the colony. This result is unlikely to be a by-product of relatives nesting in close vicinity, as nest distance and genetic identity are not correlated. For eider females that had been ring-marked during the decades prior to our study, our analyses indicate that (i) the average age of parasitized females is higher than the age of nonparasitized females, (ii) the percentage of nests with alien eggs increases with the age of nesting females, (iii) the level of IBP increases with the host females' age, and (iv) the number of own eggs in the nest of parasitized females significantly decreases with age. IBP may allow those older females unable to produce as many eggs as they can incubate to gain indirect fitness without impairing their direct fitness: genetically related females specialize in their energy allocation, with young females producing more eggs than they can incubate and entrusting these to their older relatives. Intraspecific brood parasitism in ducks may constitute cooperation among generations of closely related females.     

Why do grebes cover their nests? Laboratory and field tests of two alternative hypotheses

Egg predation is a common feature influencing the reproductive success of open nesting birds. Evolutionary pressure therefore favours building cryptic, inconspicuous nests. However, these antipredatory pressures may be in conflict with thermoregulatory constraints, which select for dry nest material maintaining optimum temperature inside a nest cup during the absence of incubating parents. Here we examined possible trade-offs between nest crypsis and thermoregulation in Little Grebes (Tachybaptus ruficollis), which lay their eggs in floating nests built from wet plant material. As this species regularly covers its eggs with nest material, we experimentally examined (1) the rates of egg predation on covered and uncovered artificial nests and (2) possible thermoregulatory costs from nest covering by comparing temperature and relative humidity changes inside the nest cup. Results revealed that covering clutches is beneficial in terms of deterring predators, because uncovered eggs were more vulnerable to predation. Moreover, covering clutches also had thermoregulatory benefits because the mean temperature and relative humidity inside nest cups covered by dry or wet materials were significantly higher for covered compared to uncovered treatments. Covering clutches in Little Grebes therefore does not pose thermoregulatory costs.