Factors influencing nesting success of the river lapwing, Vanellus duvaucelii (Lesson, 1826)

Nesting success is defined as the percentage of nests that have at least one chick that successfully fledges from them. In this regard, this study was conducted in the Gangetic plain of district Raebareli (Uttar Pradesh), India, to investigate nesting success, resolve factors affecting the probability of nest failure and identify the predominant nest predators of the river lapwing, Vanellus duvaucelii. The line transect method was adopted to count the nesting pairs, while nesting success was estimated by the Mayfield method. Results revealed that river lapwing nests were not homogeneously distributed at the study sites. The number of nesting pairs significantly diverged at various study sites in different years. Nesting success of river lapwings at all habitat types varied across the year of study from 67.9% in 2016, to 63.6% and 70.1% in 2017 and 2018, respectively. In all years, river lapwing nests on open, unvegetated river banks achieved significantly greater nesting success than those in crop fields. However, nest failure was mainly due to predation (55%) and farming activity (32%). Furthermore, trampling (6%) by domestic cattles such as cows and buffaloes, egg non-viability (4%), human disturbance (2%) and flooding (1%) were reported as other notable factors influencing nest failure. We also found reptiles, birds and mammals as predators of eggs in the study areas. The most common predators were crow, dog, fox and snake. There is little information regarding factors influencing nesting success of river lapwings particularly in India and therefore this study increases our knowledge of this globally near-threatened species. Developing greater understanding of the river lapwing could help us to formulate effective conservation measures for this species.

Low reproductive success of Campo Suiriri (Suiriri affinis) and Chapada Flycatcher (S. islerorum) in the central Brazilian Cerrado

We investigated the reproductive success of Campo Suiriri (Suiriri affinis) and Chapada Flycatcher (S. islerorum) in the Estação Ecológica de Águas Emendadas, Central Brazil. Between June and December 2003, we monitored 25 nests of Campo Suiriri and 20 nests of Chapada Flycatcher. The simple percentage of successful nests was 32% for Campo Suiriri and 10% for Chapada Flycatcher, whereas the reproductive success calculated by the Mayfield method was 19% for Campo Suiriri and 14% for Chapada Flycatcher. The estimated values of daily survivorship rate (DSR) for Campo Suiriri are as follows: egg period 0.971 and nestling period 0.944. For Chapada Flycatcher the figures were 0.964 and 0.930, respectively. No differences in DSRs between species or periods were statistically significant. All nest losses of Campo Suiriri were due to predation, while for Chapada Flycatcher predation accounted for 78% of nest losses and the remaining 22% was due to parasitism by botfly larvae (Philornis sp.). The low reproductive success of Chapada Flycatcher is close to the lowest values recorded for Neotropical birds and might be a threat to this species and an important variable in the determination of its conservation status.

Use of Survival Time Analysis to Analyze Nesting Success in Birds: An Example Using Loggerhead Shrikes

Ornithologists commonly estimate nest survival using the Mayfield method, which produces relatively unbiased estimates provided that key assumptions are met. However, this method cannot statistically model nest failure in relation to quantitative variables, nor can it consider the joint effects of two or more independent variables. We demonstrate the use of an alternative method, survival time analysis. Survival time analysis can incorporate nests that are found at different points in the nesting cycle and nests whose ultimate outcome is unknown. The method allows one to examine variation in nest mortality during the course of the nesting period. To demonstrate this method we analyze data on Loggerhead Shrike (Lanius ludovicianus) nests, collected as part of a 3-year monitoring program of shrubsteppe habitat in north-central Oregon. We evaluate nesting success with respect to laying date, nest height, and annual variation in failure rate. We demonstrate three types of analyses: Kaplan-Meier estimation (a nonparametric method), Cox proportional hazards model (a semiparametric method), and Weibull parametric regression. Using these maximum-likelihood methods one can carry out likelihood-ratio tests and Akaike's Information Criterion model selection. The best predictive model included the effects of date and year. Nest failure rate changed during the nesting cycle and was heterogeneous among nests, thus violating assumptions of the Mayfield method. We discuss drawbacks to the use of logistic regression (another Mayfield alternative) to analyze nest success. Estimates of the age of a nesting attempt upon discovery are required for survival time analysis; we encourage ornithologists to collect such information.Uso del Análisis de Tiempo de Sobreviviencia para Analizar el Éxito de Nidificación: Un Ejemplo Utilizando Lanius ludovicianusResumen. Los ornitólogos generalmente utilizan el método de Mayfield para estimar la sobrevivencia de los nidos, un método que produce estimaciones relativamente poco sesgadas siempre y cuando se cumplan sus suposiciones claves. Sin embargo, este método no es capaz de modelar estadísticamente los fracasos de nidificación en relación con variables cuantitativas, ni tampoco puede considerar el efecto conjunto de dos o más variables independientes. Aquí, demostramos el uso de un método alternativo, el análisis de tiempo de sobrevivencia, el cual puede incorporar nidos que son encontrados en diferentes tiempos durante el ciclo de nidificación y también nidos cuyo resultado final es desconocido. El método permite examinar la variación en la mortalidad de nidos durante el transcurso del período de nidificación. Con el fin de demostrar este método, analizamos datos de nidos de Lanius ludovicianus colectados como parte de un programa de monitoreo del hábitat de estepa arbustiva durante un período de 3 años en Oregon nor-central. Evaluamos el éxito de nidificación con respecto a la fecha de puesta, altura del nido y variación anual en la tasa de fracaso. Demostramos tres tipos de análisis: estimación de Kaplan-Meier (un método no paramétrico), modelos de riesgo proporcional de Cox (un método semi paramétrico) y regresión paramétrica de Weibull. Utilizando estos métodos de máxima verosimilitud uno puede seleccionar modelos realizando pruebas de cocientes de verosimilitudes y utilizando el criterio de información de Akaike. El modelo con mayor capacidad predicativa incluyó los efectos de la fecha y el año. La tasa de fracaso de nidos varió durante el ciclo de nidificación y fue heterogénea entre nidos violando así, las suposiciones del método de Mayfield. Discutimos las desventajas del uso de regresiones logísticas (otra alternativa al método de Mayfield) para el análisis del éxito de los nidos. Para el análisis de tiempo de sobreviviencia se requiere la estimación de la edad de un intento de nidificación en el momento de ser descubierto, por lo que sugerimos a los ornitólogos colectar dicha información.

Nest Survival Estimation: A Review of Alternatives to the Mayfield Estimator

Reliable estimates of nest survival are essential for assessing strategies for avian conservation. We review the history of modifications and alternatives for estimating nest survival, with a focus on four techniques: apparent nest success, the Mayfield estimator, the Stanley method, and program MARK. The widely used Mayfield method avoids the known positive bias inherent in apparent nest success by estimating daily survival rates using the number of exposure days, eliminating the need to monitor nests from initiation. Concerns that some of Mayfield's assumptions were restrictive stimulated the development of new techniques. Stanley's method allows for calculation of stage-specific daily survival rates when transition and failure dates are unknown, and eliminates Mayfield's assumption that failure occurred midway through the nest-check interval. Program MARK obviates Mayfield's assumption of constant daily survival within nesting stages and evaluates variation in nest survival as a function of biologically relevant factors. These innovative methods facilitate the evaluation of nest survival using an information-theoretic approach. We illustrate use of these methods with Lark Bunting (Calamospiza melanocorys) nest data from the Pawnee National Grassland, Colorado. Nest survival estimates calculated using Mayfield, Stanley, and MARK methods were similar, but apparent nest success estimates ranged 1– 24% greater than the other estimates. MARK analysis revealed that survival of Lark Bunting nests differed between site–year groups, declined with both nest age and time in season, but did not vary with weather parameters. We encourage researchers to use these approaches to gain reliable and meaningful nest survival estimates.Estimación de la Supervivencia de Nidos: Una Revisión de las Alternativas del Estimador MayfieldResumen. Es esencial contar con estimaciones confiables de la supervivencia de nidos para evaluar las estrategias de conservación de las aves. Revisamos la historia de modificaciones y las alternativas para estimar la supervivencia de nidos, enfocándonos en cuatro técnicas: éxito aparente del nido, el estimador de Mayfield, el método de Stanley y el programa MARK. El método de Mayfield, ampliamente usado, evita el conocido sesgo positivo inherente al éxito aparente del nido mediante la estimación de tasas de supervivencia diaria usando el número de días de exposición, eliminando así la necesidad de monitorear los nidos desde el inicio. Las preocupaciones de que algunos de los supuestos del método de Mayfield son restrictivos estimularon el desarrollo de nuevas técnicas. El método de Stanley permite el cálculo de tasas de supervivencia diarias específicas para cada etapa cuando las fechas de transición y fracaso son desconocidas, y elimina el supuesto del método de Mayfield que sostiene que el fracaso ocurre en el medio del intervalo de monitoreo del nido. El programa MARK elimina el supuesto del método de Mayfield sobre supervivencia diaria constante dentro de las etapas de nidificación y evalúa la variación en la supervivencia de nidos como función de factores biológicamente relevantes. Estos métodos innovadores facilitan la evaluación de la supervivencia de nidos usando un enfoque teórico-informativo. Ilustramos el uso de estos métodos con datos de nidos de Calamospiza melanocorys provenientes de Pawnee National Grassland, Colorado. Las estimaciones de supervivencia de los nidos calculadas usando los métodos de Mayfield, Stanley y MARK fueron similares, pero las estimaciones del éxito aparente de los nidos fueron entre 1–24% mayores que las otras estimaciones. Los análisis con MARK revelaron que la supervivencia de los nidos de C. melanocorys difirió entre grupos de sitio-año, disminuyó con la edad del nido y el tiempo de la estación, pero no varió con parámetros climáticos. Estimulamos a los investigadores a usar estos enfoques para obtener estimaciones de supervivencia de nidos confiables y válidas.

Mayfield Logistic Regression: A Practical Approach for Analysis of Nest Survival

Mayfield logistic regression is a method for analyzing nest-survival data that extends the traditional Mayfield estimator by incorporating explanatory variables (e.g. habitat structure, seasonal effects, or experimental treatments) in a logistic-regression analysis framework. Although Aebischer (1999) previously showed that logistic regression can be used to fit Mayfield models, few ornithologists have put that finding into practice. My purpose here is to reintroduce this underused method of nest-survival analysis, to compare its performance to that of a dedicated survival-analysis program (MARK), and to provide a practical guide for its use. Like the traditional Mayfield method, Mayfield logistic regression accounts for the num ber of “exposure days” for each nest and allows for uncertain fates (censoring), thus avoiding the bias introduced by typical applications of logistic regression. Mayfield logistic regression should be widely applicable when nests are found at various stages in the nesting cycle and multiple explanatory variables influencing nest survival are of interest.

Life history of the white-breasted robin, Eopsaltria georgiana (Petroicidae), in south-western Australia

The white-breasted robin, Eopsaltria georgiana, is endemic to south-western Australia. We studied breeding, dispersal and survival in known groups from 1978 until 1987, with some groups followed until 1992, in Eucalyptus diversicolor (karri) forest near Manjimup, Western Australia. E. georgiana bred cooperatively, with 66% of groups including one or more birds in addition to the breeding pair (mean group size 3.1); these helpers were predominantly males and assisted the senior male in feeding the female on the nest and the young and defending the territory. The survival of adults was high (males 86%; females 79%). Breeding territories and groups persisted from year to year, although in the non-breeding season, males ranged more widely. Dispersal was female-biased; most females and some males dispersed in their first year. Divorce was rare; breeding males that disappeared were replaced by a helper from within the group if one was present, and females were replaced from outside the group. Eggs were laid between July and December. Clutch size was almost always 2, incubation lasted 16–17 days and nestlings fledged 13–14 days later. Juveniles were dependent on adult provisioning for 6–8 weeks. We found no parasitism by cuckoos. Of 429 nests found, 74% fledged at least one young, and overall nesting success calculated by the Mayfield method was 63%. The median time between initiation of two successive clutches was 54 days, and 52% of females renested after fledging one brood; at least two broods per year were fledged by 44% of females. Groups produced a mean of 2.8 fledglings, 1.3 independent young and 0.7 yearlings per year. The most productive groups were those with two or more helpers on high-quality territories, but we could not separate the effects of helpers and territory quality. E. georgiana has the 'slow' life history typical of many Australian passerines – cooperative breeding, sedentary, resident all year round in an equable habitat that promotes high survival of breeding adults. Their low reproductive rate produces a small crop of yearlings, some of which may stay in the parental home range.

Reproductive Ecology and Demography of the ‘ĀKohekohe

The ‘Ākohekohe (Palmeria dolei) is an endangered Hawaiian honeycreeper endemic to the montane rain forests of east Maui in the Hawaiian Islands. We investigated ‘Ākohekohe nesting ecology using color-banded birds for the first time as a background to understanding the species' conservation. From 1994–1997, we color-banded 78 individuals, located and monitored 46 active nests, and took behavioral data during 534 hr of nest observation at Hanawī Natural Area Reserve, near the center of the species' range. ‘Ākohekohe nesting behavior and life history closely resembled that of ‘Apapane (Himatione sanguinea) and related honeycreepers. The birds were monogamous within and among years, and we found no evidence of polyandry, polygyny, or helpers at the nest. The nesting season extended from November to early June. Females performed all incubation and brooding. Males provisioned females and nestlings, and they were more active than females in feeding fledglings during the two-week period of parental dependency. Modal clutch size, as determined from egg counts at three nests and by counting begging chicks at other nests, was two eggs, and parents frequently fledged two chicks. We found an overall nest success rate of 68% by the Mayfield method, a high rate compared with other Hawaiian honeycreepers and continental passerines. An average of 1.1 chicks fledged per active nest, and at least 42% of nesting pairs made two or more nesting attempts per season. Rats (Rattus spp.) were abundant at the study site, and we confirmed their depredating some ‘Ākohekohe nests, so we did not expect to find such a high rate of nest success. The estimated annual probability of adult survival was also high, at 0.95 ± 0.10 (SE).Ecología Reproductiva y Demografía de Palmeria doleiResumen. Palmeria dolei es una especie de mielero amenazada endémica de las selvas nubladas de montaña del Este de Maui en las Islas de Hawai. Investigamos la ecología de nidificación de esta especie usando aves marcadas con anillos de colores como antecedente para entender la conservación de la especie. Entre 1994–1997 marcamos 78 individuos, localizamos y monitoreamos 46 nidos activos, y recolectamos datos de comportamiento durante 534 hr de observación de nidos en la Reserva Natural Hanawī, cercana al centro del rango de distribución de la especie. El comportamiento de nidificación y la historia de vida de P. dolei son marcadamente similares a los de Himatione sanguinea y otros mieleros relacionados. Las aves fueron monógamas dentro y entre años, y no hallamos evidencias de poliandría, poliginia, o ayudantes en los nidos. La estación de nidificación se extendió desde noviembre hasta principios de junio. Las hembras realizaron toda la incubación y cuidado de la nidada. Los machos aprovisionaron a las hembras y pichones, y fueron más activos que las hembras en alimentar a los volantones durante las dos semanas que dependen de los padres. La moda del tamaño de la nidada, determinada a partir del conteo de huevos en tres nidos y del recuento de gritos de llamada de pichones, fue de dos huevos, y los padres generalmente lograron criar dos pichones. Encontramos una tasa de éxito global de los nidos del 68% estimada con el método Mayfield, lo que representa una alta tasa comparada con la de otros mieleros hawaianos y paseriformes continentales. Un promedio de 1.1 pichones por nido activo llegaron a la etapa de dejar el nido, y al menos 42% de las parejas nidificantes realizaron dos o más intentos de nidificación por estación. Ratas (Rattus spp.) fueron abundantes en el sitio de estudio, y confirmamos que depredan nidos de P. dolei, por lo que no esperabamos obtener una tasa de éxito de nidificación tan alta. La probabilidad estimada de supervivencia de los adultos fue también alta, 0.95 ± 0.10 (ES).

Uncertain Nest Fates in Songbird Studies and Variation in Mayfield Estimation

Determining whether nesting attempts are successful can be difficult. Yet, current protocols for estimating nesting success do not address how uncertain nest fates should be handled. We examined the problem of nest-fate uncertainty as it relates to Mayfield estimation of nesting success and in analyses of factors that influence success. We used data from Minnesota to illustrate the potential effect of uncertain fate; 40% of Ovenbird (Seiurus aurocapillus; n = 127) nests and 30% of Least Flycatcher (Empidonax minimus; n = 144) nests had uncertain fates. How this uncertainty is incorporated into Mayfield estimates of success varied widely among researchers. In a survey of researchers who use the Mayfield method, 9 of 22 respondents (of 40 contacted) excluded nests with uncertain fate. Excluding uncertain fates is counter to how Mayfield first described his estimator and can result in severe downward bias. The remaining respondents (59%) included nests with uncertain fate but varied in how they terminated the exposure period. We developed a simulation model that calculated Mayfield estimates using different approaches and compared them with a known rate of nesting success. Magnitude of bias in Mayfield estimates varied considerably in our simulations. The approach with the least bias terminated exposure with the last observed active date for nests with uncertain fate, and with the midpoint between last observed active and first observed inactive dates for nests with known fate. In addition, information necessary to interpret and compare Mayfield estimates often is not reported. These values, including variance estimates and the period lengths used to estimate survival rates, should be reported with Mayfield estimates. Finally, nest fate is commonly used as a categorical variable in studies of factors affecting nesting success. In this approach, however, nests with uncertain fate must be excluded. An alternative approach is Cox regression, which incorporates nests with uncertain fate.