High Nest Density Research Articles

Analysing spatial correlation of weeds and harvester ants in cereal fields using point processes

The interaction between the spatial distribution of weed richness and weed cover and the spatial location of harvester ant nets was investigated in cereal fields. The understanding of such interdependencies can be relevant to understand weed population dynamics in dryland cereal fields and may enhance management strategies for weed control. We used spatial statistical tools derived from point process theory. In particular, we compared the two spatial configurations by assuming two different point patterns. We did so by replacing the random weed fields by a related point pattern and comparing it with the point pattern of harvester ants. Our results suggest that areas with a high density of ant nests are, in this case study, in areas with low weed richness and that large nests have a greater impact than small nests. Considering that only one field was analysed, preserving and enhancing regular ant nest distributions, especially of large nests, might have an impact on depleting weeds and consequently enhancing weed control.

Paternal behaviour in a socially monogamous but sexually promiscuous passerine bird

We documented parental behaviour and paternity of eastern kingbirds (Tyrannus tyrannus) to test the predictions that paternal care would decline with increasing loss of paternity, increasing nesting density (a proxy for probability of paternity loss), male quality, and number of fertile females available in the population. Extra-pair young were found in 58% of 45 nests for which behaviour was recorded and a higher proportion of young were extra-pair as nesting density increased. Male feeding rate declined with increasing nesting density and male quality, but neither feeding rate nor a composite measure of paternal behaviour varied with number of fertile females or paternity. Although alternative explanations exist, one interpretation of the reduced paternal care at high nesting density was that it was a response to perceived threats of paternity loss. The ultimate basis for the lower paternal effort of higher quality males is unclear but we discuss several possible explanations.

Nest usurpation by a common eider toward a long-tailed duck

Intraspecific and non-obligate brood parasitism and nest takeover is well documented in common eiders ( Somateria mollissima borealis ) nesting in the Arctic. However, we report the takeover of a long-tailed duck ( Clangula hyemalis ) nest by a female common eider on Nasaruvaalik Island, Nunavut, Canada. The high nesting density due to limited habitat in the region may have contributed to this seemingly risky behaviour, which provides no clear benefits to the eider. Keywords: Nest takeover; sea ducks; Somateria mollissima ; Clangula hyemalis ; High Arctic; limited habitat. (Published: 26 October 2016) Citation: Polar Research 2016, 35 , 32414, http://dx.doi.org/10.3402/polar.v35.32414

Changes in habitat use and nesting density in a declining seabird colony

AbstractSeabirds in expanding colonies select the highest‐quality nesting habitat, but habitat selection has seldom been studied in declining colonies. We studied a colony of Magellanic penguins (Spheniscus magellanicus) that declined from 314,000 active nests in 1987 to 201,000 in 2014. As expected, nest quality and reproductive success were higher in burrow habitats than in other habitats, and nest density decreased with distance from shore. Contrary to predictions, the steepest declines did not occur in the poorest‐quality habitat (scrub) or near the inland colony edge and the colony area did not shrink. In agreement with predictions, penguins shifted from nests with less cover to nests with more cover. The highest nest densities and the steepest declines were in habitats of large bushes and bush clusters. As the population declined penguins abandoned nests on the edges of large bushes. Constraints on penguin habitat‐use changes include strong area and nest‐site fidelity, increased avian predation in high‐density areas, soil characteristics, and the costs of making and maintaining nests. Contrary to conventional wisdom we found low‐density, poor‐quality scrub habitat (which covers >70 % of the colony area) contained 45 % of active nests, produced 44 % of fledglings, and was as important as high‐quality habitat for reproductive output. Our research shows that all habitats in a declining colony of seabirds have value for conservation.

Anthropogenically-Mediated Density Dependence in a Declining Farmland Bird

Land management intrinsically influences the distribution of animals and can consequently alter the potential for density-dependent processes to act within populations. For declining species, high densities of breeding territories are typically considered to represent productive populations. However, as density-dependent effects of food limitation or predator pressure may occur (especially when species are dependent upon separate nesting and foraging habitats), high territory density may limit per-capita productivity. Here, we use a declining but widespread European farmland bird, the yellowhammer Emberiza citrinella L., as a model system to test whether higher territory densities result in lower fledging success, parental provisioning rates or nestling growth rates compared to lower densities. Organic landscapes held higher territory densities, but nests on organic farms fledged fewer nestlings, translating to a 5 times higher rate of population shrinkage on organic farms compared to conventional. In addition, when parental provisioning behaviour was not restricted by predation risk (i.e., at times of low corvid activity), nestling provisioning rates were higher at lower territory densities, resulting in a much greater increase in nestling mass in low density areas, suggesting that food limitation occurred at high densities. These findings in turn suggest an ecological trap, whereby preferred nesting habitat does not provide sufficient food for rearing nestlings at high population density, creating a population sink. Habitat management for farmland birds should focus not simply on creating a high nesting density, but also on ensuring heterogeneous habitats to provide food resources in close proximity to nesting birds, even if this occurs through potentially restricting overall nest density but increasing population-level breeding success.

Cooperative incubation behaviour in a super dense Common Eider Somateria mollissima colony

Capsule Common Eiders at Rif in west Iceland commonly show joint nest attendance, which may be an exaggerated behavioural response to the visual stimulus of many nests so close to their own nest. This represents a new insight into incubation behaviour in colonies with extremely high nest densities.

A Comparison of Direct and Distance Sampling Methods to Estimate Abundance of Nesting Gulls

We compared the performances of the strip transect count method and the distance sampling method during colony surveys of large gulls to estimate the total number of nests. Ten colonies were surveyed by both methods. Nest detection probabilities varied from 0.519 ± 0.064 to 0.706 ± 0.049 and the average nest detection probability was 0.614 ± 0.015. Nest densities were highly variable, ranging from 77 nests/ha to 717 nests/ha. Estimates of the number of nests obtained by the strip transect count method averaged 9.3% lower than those obtained by distance sampling but by as much as 31% in some colonies. Underestimation by the strip transect counts increased at high nest densities (Kendall t = -0.556, P = 0.032). The strip transect method needed on average 6.5 observers per colony surveyed, whereas the distance sampling method required 1.4 observers per colony. In addition, the mean time spent per colony was 3 hours vs 1.7 hours for the strip transect and distance sampling methods respectively. Combining both these measures of effort, distance sampling required on average 87% less effort in the field than the strip transect method. We strongly advocate the use of distance sampling for surveys of large gull colonies.

Should I Stay or Should I Go: Influences on Roseate Terns' (Sterna dougallii) Decisions to Move the Chicks

In this study, we investigated the relative influence of habitat variables on the decision by Sterna dougallii (Roseate Tern) parents to move from (movers) or to stay at (stayers) the nest after chick hatch. At Country Island, NS, Canada, 75% of the 21 Roseate Tern breeding pairs in this study were movers. Using a model-selection approach, we found that the chicks were more likely to be moved from nest sites in cobble beach habitat with low vegetation height and high nest densities of congener terns. However, differences in reproductive parameters among movers and stayers were not statistically significant. Though we could not establish whether moving the chicks or staying were adaptive strategies, we provide firm evidence that Roseate Tern chicks are moved to areas of lower tern densities. Chicks move further away from other terns as they age, perhaps as a mechanism to avoid kleptoparasitism as their nutritional requirements increase. Based on our findings, Roseate Terns appear more likely to rear their chicks to fledging at the original nest site when nest densities of other tern species are low (≤0.02 nests/m2) in highly vegetated areas. Thus, to enhance Roseate Tern productivity in places where they are endangered, such as Atlantic Canada, we suggest that species recovery programs place artificial nest cover, e.g., next boxes and wooden logs, in areas with potential for taller vegetation growth that are suboptimal nesting habitat for S. paradisaea (Arctic Tern)and S. hirundo (Common Tern).

Pine forest lichens under eutrophication generated by a great cormorant colony

AbstractLichen community changes were investigated on trees within a colony of great cormorants (Phalacrocorax carbo sinensis) established in a pine forest on the Curonian Spit, western Lithuania. The impact of birds on the forest has altered the number and characteristics of substrata available to lichens. The lowest number of lichen species and occurrences was registered on trees in the most active part of the colony with the highest nest density. Lichen community patterns were most strongly related to P and Ca content in substrata and pH values. Some acidophytic species showed negative correlations, both with long-term and short-term ornithogenic influence. However, three acidophytes (Chaenotheca ferruginea, Lepraria incana, Coenogonium pineti) demonstrated an affinity for the transitional zone and recently occupied trees, and furthermore,C. pinetiapparently reacted positively to a short-term ornithogenic influence but negatively to a long-term one. These three lichens, along with algae, were the main, and often the only, components of epiphytic communities on trees at the edge of the colony and apparently indicated the crucial point of the acidophytic community under the increasing load of nutrients. All nitrophytic species showed an affinity for a long-term bird influence and reacted negatively to a short-term influence. Only free-living algae (predominating speciesDesmococcus olivaceus) showed a clear affinity for trees occupied by bird nests.Hypogymnia physodeswas found to be an indicator for early environmental changes following eutrophication. The study also showed that high concentrations of P did not have a mitigating effect on the detrimental impact brought about by increases in N and pH levels, but was possibly equally detrimental to acidophytic lichens.

Examining seasonal patterns of space use to gauge how an accipiter responds to urbanization

As humans continue to rapidly develop natural landscapes, understanding how urbanization affects native species becomes increasingly important. Exploring how animals use urban environments can help assess how urban development may affect them, especially when compared to their use of non-urban environments. We examined seasonal patterns of habitat selection and space use of adult, male Cooper's hawks (Accipiter cooperii) in an urban environment to evaluate how this native resident responds to urbanization. Patterns of space use and habitat selection were uniform in both the breeding and non-breeding seasons. Average size of home ranges was among the smallest reported for the species, and did not vary in the breeding and non-breeding seasons. Hawks selected land-use types containing large non-native trees and tracts of remnant native vegetation that supported abundant prey species, in both the breeding and non-breeding seasons. Consistency in habitat selection and space use across seasons, small space requirements, and high nesting density likely reflects the high productivity of this urban environment. Comparison of patterns of space use and demographic attributes to Cooper's hawks inhabiting natural environments suggests that habitat for Cooper's hawks in this urban environment may be of higher quality than in some undeveloped areas as a result of human landscaping activities. Although most native species are negatively impacted by urbanization, some species, such as Cooper's hawks, appear to benefit from the changes wrought by development. Investigating how anthropogenic activities influence space use of native species can help managers assess the quality of urban environments as habitat.

Hard times in the city - attractive nest sites but insufficient food supply lead to low reproduction rates in a bird of prey.

IntroductionUrbanization is a global phenomenon that is encroaching on natural habitats and decreasing biodiversity, although it is creating new habitats for some species. The Eurasian kestrel (Falco tinnunculus) is frequently associated with urbanized landscapes but it is unclear what lies behind the high densities of kestrels in the urban environment.ResultsOccupied nest sites in the city of Vienna, Austria were investigated along a gradient of urbanization (percentage of land covered by buildings or used by traffic). Field surveys determined the abundance of potential prey (birds and rodents) and the results were compared to the birds’ diets. A number of breeding parameters were recorded over the course of three years. The majority of kestrels breed in semi-natural cavities in historic buildings. Nearest neighbour distances (NND) were smallest and reproductive success lowest in the city centre. Abundance of potential prey was not found to relate to the degree of urbanization but there was a significant shift in the birds’ diets from a heavy reliance on rodents in the outskirts of the city to feeding more on small birds in the centre. The use of urban habitats was associated with higher nest failure, partly associated with predation and nest desertion, and with significantly lower hatching rates and smaller fledged broods.ConclusionsHigh breeding densities in urban habitats do not necessarily correlate with high habitat quality. The high density of kestrel nests in the city centre is probably due to the ready availability of breeding cavities. Highly urbanized areas in Vienna are associated with unexpected costs for the city dwelling-raptor, in terms both of prey availability and of reproductive success. The kestrel appears to be exploiting the urban environment but given the poor reproductive performance of urban kestrels it is likely that the species is falling into an ecological trap.

Nesting ecology of <i>Chelonia mydas</i> (Testudines: Cheloniidae) on the Guanahacabibes Peninsula, Cuba

The nesting colony of green sea turtles (Chelonia mydas) at Guanahacabibes Peninsula Biosphere Reserve and National Park is one of the largest in the Cuban archipelago; however, little information about its nesting ecology is available. Temporal and spatial variation in nesting and reproductive success as well as morphometric characteristics of gravid females were used to ecologically characterize this colony. Nine beaches of the Southernmost coast of Guanahacabibes Peninsula were monitored for 14 years (1998-2012) to determine green turtle nesting activity, from May to September (peak nesting season in this area). Beach dimensions were measured to determine nest density using the length and the area. Afterward the beaches were divided in two categories, index and secondary. Females were measured and tagged to compare new tagged females (823) with returning tagged females (140). Remigration interval was also determined. Temporal variation was identified as the annual number of nesting emergences and oviposits per female, with apparent peaks in reproductive activity on a biennial cycle in the first six years followed by periods of annual increase in nest number (2003-2008) and periods of decreasing number of nests (2010-2012). We also found intra-seasonal variation with the highest nesting activity in July, particularly in the second half of the month. The peak emergence time was 22:00-02:00 hr. In terms of spatial variation, smaller beaches had the highest nest density and nesting was more frequent 6-9m from the high tide line, where hatchling production was maximized although hatchling success was high on average, above 80%. Morphometric analysis of females was made and newly tagged turtles were smaller on average than remigrants. Our results are only a first attempt at characterizing Guanahacabibes' populations but have great value for establishing conservation priorities within the context of national management plans, and for efficient monitoring and protection of nesting beaches.

Adoption and infanticide in an altricial colonial seabird, the Blue-footed Booby: the roles of nest density, breeding success, and sex-biased behavior

We aimed to elucidate the factors that influence the frequency of adoption and infanticide in the Blue-footed Booby (Sula nebouxii), a seabird with biparental chick care and high chick-rearing costs. We obtained data from two colonies during four breeding seasons. In addition, we removed parents from their nests for short periods of time (10 min) and fitted their chicks with polyethylene foam protectors, in order to record chick behavior, particularly interactions with neighboring adults. Adoption and infanticide occurred mostly in zones of high nest density and during years of high breeding success. The chicks adopted were 20–40 days of age, the age at which they acquire mobility and parents still experience a certain inability to recognize them. Adopted chicks were slightly younger than chicks in the broods into which they were adopted. In most cases, adoptees were younger than their siblings in their natal broods. We also recorded short-term (lasting only a few hours) alloparental care for chicks older than 40 days. When we excluded parents from nests and their chicks were attacked, it was female neighbors that physically attacked them, whereas males were more prone to brood or preen them; therefore, the sex with certainty of parenthood was more prone to practice infanticide, presumably to avoid adoption. The lack of aggressiveness by males might be due to the possibility of paternity, given the occurrence of extra-pair copulations in this species.

Monitoring design for quantification of marine turtle nesting with limited effort: a test case in the Guadeloupe archipelago

AbstractThe Guadeloupe archipelago hosts nesting of the threatened hawksbill Eretmochelys imbricata, green Chelonia mydas and leatherback Dermochelys coriacea marine turtles. There is a need to monitor the nesting of these species but, with > 150 beaches in the archipelago, exhaustive monitoring is infeasible. Using a new monitoring design and a new statistical tool we have been able to monitor one-third of the beaches. Seasonality and level of nesting were described for the three species for 2 years on > 50 beaches. For each species beaches were categorized as A- or B-beaches, with high and low nest density, respectively. A-beaches were monitored on 6–7 days per month before and after the peak nesting period and on 7–15 days during the peak, and the B-beaches on 14–22 days during the peak. The monitoring design and statistical tool are described in detail as they could be applied to any migratory species. Hawksbill turtles at Trois Ilets beach have been monitored for 9 years and a positive trend in nesting has been detected.

Impact of abundant Pheidole ant species on soil nutrients in relation to the food biology of the species

Impact of Pheidole sp., reportedly important in insect pest suppression in agroecosystems was studied on supporting agroecosystem services. This tropical ant species was found to be common and abundant in agroecosystems, with a high nest density and preference for the central, crop-growing zone of annual cropping systems. Physico-chemical characteristics of the debris soil were examined from nests located by the roadside and within two managed ecosystems. The debris soil had significantly higher concentrations of total C, N, P and NO3-N along with higher water-holding capacity and moderate-sized soil particles in comparison to the control soil. The pH of the Pheidole sp. debris soil was shifted towards reduced alkaline conditions. Results reveal that annually, 2.44kg/haC, 0.071kg/haP, 0.628kg/haN and 0.009kg/haNO3-N are added to the soil through the accumulation of organic refuse at the nest rim. This contributes to soil nutrient enhancement and is suggested to enhance ecosystem productivity. The high nutrient content of nest debris soil is linked to the predominance of arthropod carcasses (93.7% of the total organic refuse) in the refuse piles derived from the animal-based food (70.3%) brought to the nests by the foragers. Plant-based food was 29.6% (seeds, leaves, roots, etc.) of the total indicating a minor role of Pheidole sp. as a seed harvester. The results suggest an important role of Pheidole sp. in regulating the soil nutrients as an ecosystem engineer.

Quantification of cormorant litter and nutrient deposition to Great Lakes island ecosystems

Ornithogenic nutrients derived from waterbirds such as the double-crested cormorant (Phalacrocorax auritus, Lesson) have been linked to habitat change within nesting colonies. For the islands of Lake Erie, where increasing cormorant populations and subsequent habitat change have spurred management activity, estimates of the quantity and chemical characteristics of avian-derived contributions are lacking. To evaluate the quantity and chemical characteristics of ornithogenic litterfall beneath a double-crested cormorant colony on a western Lake Erie island we investigated the mass of material and nutrient composition (PO43−, NO3− and NH4+) reaching the forest floor under three nest densities (Low: 1–96 nestsha−1; Medium: 97–255 nestsha−1 and High: >255 nestsha−1). As expected, litterfall (total mass) input differed among nest densities with the most substantial input (225.05g/m2week−1) measured under High nest density conditions. Nutrient concentrations also showed increases with nest density to a point, where mean PO43− and NH4+ concentrations showed no differences between Medium and High nest density sites. As well, NO3− concentrations were highest under Medium density, with no differences in this nutrient observed between Low and High density. Collectively, litterfall nutrient composition was similar to those linked to habitat changes in other waterbird colonies. Similarities in the concentrations of several nutrients between Medium and High nest density categories suggest that management actions aimed at reducing allochthonous nutrient contributions should try to sustain nest density at or below 96 nestsha−1.

Predator‐mediated interactions between preferred, alternative and incidental prey in the arctic tundra

Apparent competition between prey is hypothesized to occur more frequently in environments with low densities of preferred prey, where predators are forced to forage for multiple prey items. In the arctic tundra, numerical and functional responses of predators to preferred prey (lemmings) affect the predation pressure on alternative prey (goose eggs) and predators aggregate in areas of high alternative prey density. Therefore, we hypothesized that predation risk on incidental prey (shorebird eggs) would increase in patches of high goose nest density when lemmings were scarce. To test this hypothesis, we measured predation risk on artificial shorebird nests in quadrats varying in goose nest density on Bylot Island (Nunavut, Canada) across three summers with variable lemming abundance. Predation risk on artificial shorebird nests was positively related to goose nest density, and this relationship was strongest at low lemming abundance when predation risk increased by 600% as goose nest density increased from 0 to 12 nests ha−1. Camera monitoring showed that activity of arctic foxes, the most important predator, increased with goose nest density. Our data support our incidental prey hypothesis; when preferred prey decrease in abundance, predator mediated apparent competition via aggregative response occurs between the alternative and incidental prey items.

Multicolonial population structure and nestmate recognition in an extremely dense population of the European ant Lasius flavus

Under optimal ecological conditions ant populations can reach high nest densities, leading to strong competition between colonies and affecting ant behaviour and sociogenetic structure. Extremely high population densities are commonly found in invasive ant species in which all colonies of a population act as a single super-colony with no behavioural or genetic boundaries between nests. In contrast, the typical and ancestral ant population structure consists of discrete genetic units, i.e. colonies with a single or few queens and highly related workers. The subterranean mound building ant Lasius flavus, which is native to Central Europe, reaches nest densities of up to 0.5 colonies per m2 in our study population in Southern Germany. We investigated the sociogenetic structure and its temporal stability in this dense population using genomic microsatellites. Despite close proximity, neighbouring nests were generally genetically distinct. Most mounds were inhabited by a single colony, but we also found a few polydomous colonies spreading over two or more mounds. About half of all colonies were monogynous, the others either polygynous and/or polyandrous. We re-sampled mounds after 8 months and found mound occupancy to be predominantly stable over time. Behavioural experiments revealed low aggression between workers from different nests, albeit these ants recognised their nestmates. Our study demonstrates that native ant species can reach high densities despite a multi-colonial population structure and that intense competition does not invariably lead to high aggression between nests.

Double-Crested Cormorant (Phalacrocorax auritus) Nesting Effects on Understory Composition and Diversity on Island Ecosystems in Lake Erie

The context for this study is the management concerns over the severity and extent of the impact of cormorants on island flora in the recent past on Lake Erie islands. Accordingly, this study sought to quantify the nesting colonies' influence on coarse woody litter and how nest densities and litter depth may influence the herbaceous layer, the seed bank composition and viability across the extent of three Lake Erie islands. The data for this study were collected from 2004 to 2008 on East Sister Island and Middle Island using two main strategies. First, herbaceous layer surveys, cormorant nest counts, soil seed bank cores, and litter depth measurements were executed using a plotless-point quarter method to test island-wide impacts from nesting activities (data were also collected on a third island, West Sister Island as a reference for the other two islands). Secondly, a sub-sample of the entire plot set was examined in particularly high nesting density areas for two islands (Middle Island and East Sister Island). Kruskal-Wallis tests indicated that there are subtle changes in the herbaceous diversity (total, native and exotic) and seed bank composition across the islands. The sub sample set of the plots demonstrated that Phalacrocorax auritus nest density does influence litter depth, herbaceous species abundance and diversity. Cormorant nesting pressures are restricted to areas of high nesting pressures and competition. However, there remains a risk to the interior herbaceous layer of the island if the effects of nesting pressures at the edges advance inward from this perimeter.

Macroscopic and microscopic studies of the nests and the stages involved in the nesting process of Centris muralis Burmeister (Hymenoptera: Apidae: Centridini) bee in the adobe walls, in La Rioja, Argentina

Centris (Wagenknechtia) muralis Burmeister is one of the most common bee species distributed in the xeric region of Argentina. This work describes macro-and micromorphological aspects of the nesting architecture and the stages involved in the process of nesting of C. muralis bee, in the adobe walls of Capayan ruins and recent earthen constructions in Udpinango and Villa Castelli, La Rioja, Argentina. In addition, we discuss the possible factors that may explain the high density of nests observed in the adobe walls of Capayan ruins. These constructions are settled in the northern area of the Monte desert. Our analysis showed that the nest cell walls are strengthened and waterproofed probably by the admixture of organic material to the adobe matrix. Light microscopy of thin sections of the vacated cells showed the inner layers of organic material corresponding to the cocoon, and the outer layer of 0.7 mm thick corresponding to the cell walls consisting mainly of silt and clay, fine sand grains in low rate and absence of grains of sand medium and large. The cell wall was not different in its granulometry from that in the adobe brick, thus suggesting that the cell wall was constructed probably by cementing the particles with bee secretion. The scanning micrographs showed that the cell walls and non-nesting zones exhibited abundant clay crystals in the grain distribution. Pollen from Larrea sp. was observed in high proportions in the nest contents of C. muralis in the Capayan adobe walls.