Length Of Breeding Season Research Articles

BREEDING BIOLOGY OF PASSERINES IN THE SUBTROPICAL BRAZILIAN ATLANTIC FOREST

Information on breeding biology of birds is fundamental for the understanding of life history evolution and conservation. This information is only beginning to accumulate for Neotropical birds but the southern subtropics are still overlooked. Here we describe the breeding biology of passerines in subtropical Brazilian Atlantic Forest. We monitored 265 nests of 38 species during the 2012–2013 breeding season. Breeding began in September, but some species started as late as December. Average breeding season length was 64 days, but varied broadly across species. Average clutch sizes ranged from two to five eggs. The breeding season phenology, clutch sizes, and nesting periods were similar to other two communities at the same latitude in Argentina. Our data contribute to the debate that the combination of small clutch sizes and short breeding seasons seen in subtropical South America challenges the tropical-temperate paradigm of life-history theory.

Do individual breeding experience and parental effort affect breeding season length in blackbirds?

Weather is a crucial factor affecting the onset and end of breeding in birds. However, a few studies have clearly indicated that other factors—breeding parameters and/or individual traits—can also exert an influence. Our study aimed to determine how breeding experience and parental investment are related to the start and the end of the breeding season. We used age and pair-bond duration as predictors of breeding experience. We presumed, firstly, that older birds with a longer pair-bond duration would start breeding earlier, and secondly, that greater parental investment (expressed as breeding success in the previous season) favored later breeding. We tested the above hypotheses on an urban population of blackbirds (Turdus merula) in 2 parks in the city of Szczecin (western Poland) over 19 years. Despite the importance of weather variables, breeding experience expressed as age and pair-bond was shown to be a significant factor, too. Older birds with more bond experience started breeding sooner. Toward the end of the breeding season older, more experienced birds prolonged this period. We also observed senescence, which was manifested as the shortening of the breeding season. Those birds with more success in the previous season prolonged their breeding period in the following season; this contradicted our hypothesis. Temperature and precipitation were negatively related to the initiation date of the first clutch but positively to the initiation date of the last one. Our survey clearly showed the importance of breeding experience with the same partner and underlined the advantages of monogamy.

PregCard study: assessing the impact of routine management strategies on reproductive performance of beef herds in the upper Great Plains

Summary data from pregnancy examinations were submitted by participating veterinarians over a 2-year period to assess the impacts of routine management decisions on reproductive performance in beef herds. Upon completion of pregnancy examination, the PregCard was completed by indicating the number of females evaluated, number non-pregnant, female age (cows, heifers, or both), number and age (yearling, mature, or mixed) of bulls used, breeding season dates, and whether groups were exposed to artificial insemination. Data were reported by 8 clinics and included 242,967 females in 1,782 groups. Number of females/bull and breeding season were calculated for each group. Each group was also assigned to categories for females/bull, breeding group size, breeding season length, and age class of breeding bulls. Groups consisting of only cows had greater (P less than or equal to 0.01) reported pregnancy rates compared with groups consisting of only heifers (90.1% and 86.6%, respectively). Reported pregnancy rates were also influenced (P less than or equal to 0.01) by breeding group size, breeding season length, and bull age. Females/bull decisions were impacted (P less than or equal to 0.01) by breeding system (artificial insemination or natural service), and reported pregnancy rates were impacted by a breeding system x females/bull interaction (P less than or equal to 0.001). The PregCard system provided an excellent platform to gather benchmarking data and to assess the impact of routine management practices on reported pregnancy rates in beef herds in the upper Great Plains.

Ectoparasitism shortens the breeding season in a colonial bird.

When blood-feeding parasites increase seasonally, their deleterious effects may prevent some host species, especially those living in large groups where parasites are numerous, from reproducing later in the summer. Yet the role of parasites in regulating the length of a host's breeding season—and thus the host's opportunity for multiple brooding—has not been systematically investigated. The highly colonial cliff swallow (Petrochelidon pyrrhonota), a temperate-latitude migratory songbird in the western Great Plains, USA, typically has a relatively short (eight to nine week) breeding season, with birds rarely nesting late in the summer. Colonies at which ectoparasitic swallow bugs (Oeciacus vicarius) were experimentally removed by fumigation were over 45 times more likely to have birds undertake a second round of nesting than were colonies exposed to parasites. Late nesting approximately doubled the length of the breeding season, with some birds raising two broods. Over a 27 year period the percentage of birds engaging in late nesting each year increased at a colony site where parasites were removed annually. This trend could not be explained by changes in group size, climate or nesting phenology during the study. The results suggest that ectoparasitism shortens the cliff swallow's breeding season and probably prevents many individuals from multiple brooding. When this constraint is removed, selection may rapidly favour late nesting.

Weather conditions and breeding season length in blackbird (Turdus merula)

The timing of egg laying by songbirds is known to be strongly affected by local climate, with temperature and precipitation being the most influential factors. However, most research to date relates only to the start of the breeding season: later records and the duration of the whole have not been taken into consideration. In the case of multibrooded species, productivity usually depends on the length of the breeding season. In this work we analysed climatic factors affecting breeding season length of an urban blackbird (Turdus merula) population. The study was conducted in two parks in the city of Szczecin, north-western Poland, spanning 14 breeding seasons since 1997. We found that over the study period, the breeding season became shorter as a result of colder springs and possibly because of warmer June-July temperatures. Our study revealed a positive relationship between breeding season length and the mean and mean minimum temperatures in April. Total precipitation in April-July also positively influenced breeding season length. The present survey confirms the influence of temperature and precipitation on the breeding season length of blackbird.

Характер размножения и особенности гнёзд кумая в горах Тянь-Шаня, Китай

We studied the breeding biology of Himalayan Griffon ( Gyps himalayensis ) in the central Tien Shan Mountains over two years (2012/2013). Line transect surveys were used to locate breeding sites. Breeding behavior was monitored from vantage points and nest site information obtained during nest visits and from video camera footage. Nest and nest-site characteristics, breeding stage and measurements of eggs and chicks were recorded during nest visits. Our survey estimated between 89 and 122 nests located within 14 colonies at 7 localities. Himalayan Griffon preferred nesting on the south-facing slopes (78.6%). Nests were in rock cavities, small caves or on ledges. Nest material comprised principally of fine reed stalks such as Poa spp. and Stipa spp. The maximum lateral extent of a single colony was 7.3 km, and the two nearest colonies were 47 km apart. Breeding season length was between six and nine months extending from January to September. The duration of the chick-rearing period was particularly prolonged compared to that of other Gyps vultures. The potential reasons for this are discussed and future research recommended.

Feeding Rates, Double Brooding, Nest Reuse, and Seasonal Fecundity of Eastern Wood-Pewees in the Missouri Ozarks

Despite being widespread and abundant, little is known about the breeding ecology and natural history of the Eastern Wood-Pewee (Contopus virens), in part because nests are often high in the canopy, difficult to view, and adults are monomorphic. We monitored nests of Eastern Wood-Pewees and recorded the feeding rate of nestlings by adults as part of a larger study on breeding demography of Eastern Wood-Pewees across a gradient of savanna, woodland, and forest in the Missouri Ozarks in 2010–2011. We monitored 287 nests between 26 May and 22 August and conducted feeding rate observations for 54 nests with nestlings. There was an 88-day nesting season with peaks of nest activity on 24 June and 22 July. We recorded 19 cases of double brooding and nine cases of within-season nest reuse. Seasonal fecundity was 2.2 fledglings per territory. The frequency of parental feeding visits increased with nestling age. These are additional observations of nest reuse, nesting cycle lengths, and breeding season length for Eastern Wood-Pewees; future demographical research of marked individuals will continue to fill in gaps in breeding ecology for this common and widespread flycatcher.

High rates of extra‐pair paternity in two equatorial populations of rufous‐collared sparrow, Zonotrichia capensis

The latitudinal increase in extra‐pair paternity (EPP) rates in birds suggests broad selective benefits to low EPP rates in the tropics. However, we have few EPP data from tropical birds, particularly from species with close relatives at high latitudes. Here, we report EPP rates in two resident equatorial populations of rufous‐collared sparrow Zonotrichia capensis, a genus well‐represented at high latitudes. We found 64% and 60% of broods contained extra‐pair offspring, and 42% and 52% of all young were extra‐pair. EPP rates were similar in these populations, despite clear differences in elevation, temperature, rainfall, and breeding season length. These findings provide evidence that EPP rates in tropical birds can be as high as those observed in temperate birds, and suggest that the selective pressures acting on EPP rates vary markedly across tropical birds.

Phenological indices of avian reproduction: cryptic shifts and prediction across large spatial and temporal scales

Climate change-induced shifts in phenology have important demographic consequences, and are frequently used to assess species' sensitivity to climate change. Therefore, developing accurate phenological predictions is an important step in modeling species' responses to climate change. The ability of such phenological models to predict effects at larger spatial and temporal scales has rarely been assessed. It is also not clear whether the most frequently used phenological index, namely the average date of a phenological event across a population, adequately captures phenological shifts in the distribution of events across the season. We use the long-tailed tit Aegithalos caudatus (Fig. 1) as a case study to explore these issues. We use an intensive 17-year local study to model mean breeding date and test the capacity of this local model to predict phenology at larger spatial and temporal scales. We assess whether local models of breeding initiation, termination, and renesting reveal phenological shifts and responses to climate not detected by a standard phenological index, that is, population average lay date. These models take predation timing/intensity into account. The locally-derived model performs well at predicting phenology at the national scale over several decades, at both high and low temperatures. In the local model, a trend toward warmer Aprils is associated with a significant advance in termination dates, probably in response to phenological shifts in food supply. This results in a 33% reduction in breeding season length over 17 years – a substantial loss of reproductive opportunity that is not detected by the index of population average lay date. We show that standard phenological indices can fail to detect patterns indicative of negative climatic effects, potentially biasing assessments of species' vulnerability to climate change. More positively, we demonstrate the potential of detailed local studies for developing broader-scale predictive models of future phenological shifts.

How do variations in seasonality affect population cycles?

Seasonality is an important component in many population systems, and factors such as latitude, altitude and proximity to the coastline affect the extent of the seasonal fluctuations. In this paper, we ask how changes in seasonal fluctuations impact on the population cycles. We use the Fennoscandian vole system as a case study, focusing on variations in the length of the breeding season. We use a predator-prey model that includes generalist and specialist predation alongside seasonal forcing. Using a combination of bifurcation analysis and direct simulations, we consider the effects of varying both the level of generalist predation and the length of the breeding season; these are the main changes that occur over a latitudinal gradient in Fennoscandia. We predict that varying the breeding season length leads to changes in the period of the multi-year cycles, with a higher period for shorter breeding season lengths. This concurs with the gradient of periodicity found in Fennoscandia. The Fennoscandian vole system is only one of many populations that are affected by geographical and temporal changes in seasonality; thus our results highlight the importance of considering these changes in other population systems.

From home range dynamics to population cycles: Validation and realism of a common vole population model for pesticide risk assessment

Despite various attempts to establish population models as standard tools in pesticide risk assessment, population models still receive limited acceptance by risk assessors and authorities in Europe. A main criticism of risk assessors is that population models are often not, or not sufficiently, validated. Hence the realism of population-level risk assessments conducted with such models remains uncertain. We therefore developed an individual-based population model for the common vole, Microtus arvalis, and demonstrate how population models can be validated in great detail based on published data. The model is developed for application in pesticide risk assessment, therefore, the validation covers all areas of the biology of the common vole that are relevant for the analysis of potential effects and recovery after application of pesticides. Our results indicate that reproduction, survival, age structure, spatial behavior, and population dynamics reproduced from the model are comparable to field observations. Also interannual population cycles, which are frequently observed in field studies of small mammals, emerge from the population model. These cycles were shown to be caused by the home range behavior and dispersal. As observed previously in the field, population cycles in the model were also stronger for longer breeding season length. Our results show how validation can help to evaluate the realism of population models, and we discuss the importance of taking field methodology and resulting bias into account. Our results also demonstrate how population models can help to test or understand biological mechanisms in population ecology.

A comparison of the dynamical impact of seasonal mechanisms in a herbivore–plant defence system

Plant defences can reduce herbivore fitness and may promote cycles in some herbivore populations. In this study, we model the interaction between plant defences and herbivores and include seasonal forcing, a ubiquitous environmental influence in natural systems. We compare the impacts of two different seasonal mechanisms on the dynamics of the herbivore–plant defence system. The first mechanism involves a fixed breeding season length and a variable birth rate within the breeding season; the second involves a variable breeding season length and a fixed birth rate within the breeding season. When parameterised for a specific cyclic system, namely field voles and silica, our model predicts that a variable season length gives multi-year cycles for a larger region in parameter space than a variable birth rate. Our results highlight the complexity of the dynamical effects of seasonal forcing and that these effects are strongly dependent on the type of seasonal mechanism.

Variation in Testosterone and Corticosterone in Amphibians and Reptiles: Relationships with Latitude, Elevation, and Breeding Season Length

Latitudinal variation in life-history traits has been the focus of numerous investigations, but underlying hormonal mechanisms have received much less attention. Steroid hormones play a central role in vertebrate reproduction and may be associated with life-history trade-offs. Consequently, circulating concentrations of these hormones vary tremendously across vertebrates, yet interspecific geographic variation in male hormone concentrations has been studied in detail only in birds. We here report on such variation in amphibians and reptiles, confirming patterns observed in birds. Using phylogenetic comparative analyses, we found that in amphibians, but not in reptiles, testosterone and baseline corticosterone were positively related to latitude. Baseline corticosterone was negatively related to elevation in amphibians but not in reptiles. For both groups, testosterone concentrations were negatively related to breeding-season length. In addition, testosterone concentrations were positively correlated with baseline corticosterone in both groups. Our findings may best be explained by the hypothesis that shorter breeding seasons increase male-male competition, which may favor increased testosterone concentrations that modulate secondary sexual traits. Elevated energetic demands resulting from greater reproductive intensity may require higher baseline corticosterone. Thus, the positive relationship between testosterone and corticosterone in both groups suggests an energetic demand for testosterone-regulated behavior that is met with increased baseline glucocorticoid concentrations.

Breeding ecology of rice field rats, Rattus argentiventer and R. tanezumi in lowland irrigated rice systems in the Philippines

Rodents are one of the major pests in lowland irrigated rice crops in the Philippines. Rattus tanezumi occurs throughout the Philippines, whereas Rattus argentiventer does not occur on the main island of Luzon. Little is known about the breeding ecology of R. argentiventer and R. tanezumi where they coexist in the Philippines. We hypothesised that R. tanezumi breeding occurs throughout the season whereas the breeding of R. argentiventer is strongly cued to the generative stage of rice crops. We examined the breeding ecology of the two species in San Jose, Mindoro, Philippines, for four rice cropping seasons (two dry and two wet) over two years, 2009–2010, as a basis to develop effective management. We found to our surprise that their breeding ecology was similar. For both species (i) the onset of the breeding season was at the tillering stage of the rice crop; (ii) conception of adult females was highest at booting and ripening of rice; (iii) the highest litter size occurred at the ripening and stubble stages, and the lowest at tillering. Based on their breeding ecology we recommend that the most effective strategy to reduce damage to rice crops is to prevent the development of high populations of both species of rice field rats. This goal requires coordinated community control at both the sowing/planting time and maximum tillering of rice, in combination with the synchronous planting of rice to limit the length of the main breeding season.

A comparison of life‐history and parental care in temperate and tropical wrens

Comparing closely related species that live in different environments is a powerful way to understand selective pressures that influence life‐history evolution. We examined a suite of life‐history traits and parental care in neotropical buff‐breasted wrens Cantorchilus leucotis and north‐temperate Carolina wrens Thryothorus ludovicianus (Family Troglodytidae), to test hypotheses about life‐history evolution. As expected, buff‐breasted wrens exhibited smaller clutch sizes and higher annual adult survival than Carolina wrens. We found minimal support for the nest predation hypothesis, as nest survival and age‐corrected provisioning rates to whole broods were similar between species, and number of breeding attempts and breeding season length were greater in temperate wrens. Critical predictions of the food limitation hypothesis were not supported; in particular age‐corrected provisioning rates per nestling were higher in the tropical than temperate species. The adult survival and offspring quality hypothesis garnered the most support, as buff‐breasted wrens exhibited greater age‐corrected provisioning rates per nestling, a longer nestling period, longer re‐nesting intervals following nest success, and lower annual fecundity than Carolina wrens. Despite similarly prolonged breeding seasons, reproductive strategies differ between species with buff‐breasted wrens investing considerably in single broods to optimize first‐year survival and Carolina wrens investing in multiple small broods to optimize annual fecundity.

The potential for comparative research across New World bird migration systems

For a migratory bird, the costs and benefits of utilizing a given migratory strategy vary according to the biotic (e.g., physiology) and abiotic (e.g., weather) constraints it experiences throughout the year. In the New World, closely related species migrate to breeding grounds located across a wide range of latitudes, from northern North America to southern South America. Because the ultimate goal of a bird on spring migration is to successfully arrive on the breeding grounds in a timely manner, events that occur during the breeding season (e.g., amount of time available to breed) could affect, through selection pressures, the behavior of birds on spring migration. Variation across north temperate, tropical, and south temperate latitudes in breeding strategies, breeding season length, and availability of food during the breeding season has been well documented in various bird species. Thus, such factors as migratory strategies, risk of mortality on migration, and effects of climate change on migratory patterns may also vary predictably, depending on the latitude, both north and south of the Equator, at which a migratory population breeds. Comparing such patterns across the New World, using interdisciplinary approaches and the latest in technological advances, holds promise for better understanding how migratory birds accomplish these spectacular journeys.

The associations of management and demographic factors with technical, allocative and economic efficiency of Irish dairy farms

SUMMARYThe phasing out of the European Union (EU) milk quota will create opportunities for producers to expand without the constraint of quota which has limited expansion since 1984. Therefore, it will be necessary for Irish dairy producers to become more competitive by increasing performance using the least amount of inputs per unit of output and maximizing the level of technical and economic efficiency. The objectives of the current study were to measure technical, allocative and economic efficiency, and to investigate the associations of key management, qualitative and demographic characteristics on efficiency. Efficiency scores were calculated using the non-parametric methodology data envelopment analysis (DEA). The DEA results showed that on average the sample of Irish dairy producers were not fully efficient in 2008 with technical, allocative and economic efficiency results under variable returns to scale (VRS) of 0·771, 0·740 and 0·571, respectively. In a second stage analysis, Tobit regressions were used to determine the associations of key variables with the technical, allocative and economic efficiency scores. The efficiency scores were included as dependent variables and the key independent variables were a variety of management and demographic variables. Mean calving date, number of grazing days, breeding season length, milk quality, discussion group membership and soil quality were all associated with technical and economic efficiency. Milk recording, use of artificial insemination (AI) and level of dairy specialization were associated with allocative and economic efficiency only. Age and age squared were the only significant demographic associations with the efficiency scores.

Season length influences breeding range dynamics of trumpeter swans Cygnus buccinator

AbstractThe breeding range of large‐bodied waterfowl nesting in the northern boreal forest is likely influenced by breeding season length. This may be particularly true for the largest species of North American waterfowl, the trumpeter swan Cygnus buccinator, due to the extended time period necessary to raise young to fledging. This species recently recovered from near‐extinction in the early 1900s to reoccupy historic breeding areas throughout the boreal forest in Alaska, although recolonization patterns may have been influenced by variation in season length over the same time period. This may have resulted in range expansion into areas that were historically unavailable due to an ice‐free period insufficient for successful reproduction. We used hierarchical occupancy models to analyze trumpeter swan survey data collected over the entire breeding range in Alaska during 1968‐2005. We fit models containing combinations of recolonization parameters, trend and latitude, and season length to these data to determine whether these variables explained the variation in occupancy across our survey area. Support for season length parameters would provide evidence that the recolonization process was partially related to the length of the breeding season. We expected that occupancy probability would increase range‐wide due to overall population growth, while occupancy would be greatest at mid‐latitudes, near the center of the species range. Because this population was recovering, we also expected that expansion would proceed outward from the range center. Our results indicated that habitat occupancy was positively related to season length, partially explaining the recently observed northward range expansion. Our results suggest that increases in annual temperatures due to climate warming would likely be associated with further range expansion in trumpeter swans and may have implications for other wetland obligates. Changes in species distributions will likely increase competition for breeding areas with potential negative effects on species not limited by season length. This may already be occurring in Alaska where the breeding distribution of trumpeter swans has begun to overlap with that of tundra swans Cygnus columbianus.

Variable reproductive strategies of an African savanna frog, Phrynomantis microps (Amphibia, Anura, Microhylidae)

Abstract:West African savannas are habitats with unpredictable rainfall. Species with varying life-history traits may be more successful in these environments than species with fixed traits. We studied the reproduction strategies of the microhylid frog Phrynomantis microps in different savanna types, a humid savanna in Ivory Coast and a drier one in Benin. We recorded 5437 clutches in eight ponds in the humid savanna during five consecutive rainy seasons. A further 694 clutches were investigated in 10 ponds in Benin in one rainy season. For each clutch, we recorded egg numbers, deposition time, location within the pond and rainfall. Precipitation was important in triggering reproduction. However, the amount of rainfall needed differed in relation to rainy season length and total annual rainfall. Especially in years and regions with a late rainy season a threshold of minimum precipitation was needed to initiate spawning, indicating a trade-off between the need to reproduce and the survival probabilities of offspring in ponds with a high desiccation risk. Egg numbers per clutch further differed between pond sizes, breeding season length, as well as to time within the rainy season. Potential explanations for these differences, in particular desiccation and predation risks are discussed, but need further experimental support.

How predation and landscape fragmentation affect vole population dynamics.

BackgroundMicrotine species in Fennoscandia display a distinct north-south gradient from regular cycles to stable populations. The gradient has often been attributed to changes in the interactions between microtines and their predators. Although the spatial structure of the environment is known to influence predator-prey dynamics of a wide range of species, it has scarcely been considered in relation to the Fennoscandian gradient. Furthermore, the length of microtine breeding season also displays a north-south gradient. However, little consideration has been given to its role in shaping or generating population cycles. Because these factors covary along the gradient it is difficult to distinguish their effects experimentally in the field. The distinction is here attempted using realistic agent-based modelling.Methodology/Principal FindingsBy using a spatially explicit computer simulation model based on behavioural and ecological data from the field vole (Microtus agrestis), we generated a number of repeated time series of vole densities whose mean population size and amplitude were measured. Subsequently, these time series were subjected to statistical autoregressive modelling, to investigate the effects on vole population dynamics of making predators more specialised, of altering the breeding season, and increasing the level of habitat fragmentation. We found that fragmentation as well as the presence of specialist predators are necessary for the occurrence of population cycles. Habitat fragmentation and predator assembly jointly determined cycle length and amplitude. Length of vole breeding season had little impact on the oscillations.SignificanceThere is good agreement between our results and the experimental work from Fennoscandia, but our results allow distinction of causation that is hard to unravel in field experiments. We hope our results will help understand the reasons for cycle gradients observed in other areas. Our results clearly demonstrate the importance of landscape fragmentation for population cycling and we recommend that the degree of fragmentation be more fully considered in future analyses of vole dynamics.