Increased food provisioning by female Montagu's Harriers in years with food shortage weakens sex-specific roles in parental care

n many owl and raptor species, sexes have distinct parental roles. Females incubate the eggs and raise the chicks until independence, while males provide females and their chicks with food. This is believed to reduce sexual conflict over parental care as tasks do not overlap. The level of parental care is also shaped by parent-offspring conflict. The scarcity of empirical data on parental investment in species with sex-specific parental roles was our motivation to study parental care in the Montagu’s Harrier Circus pygargus in relation to natural annual variation in food availability (vole abundance). By tracking individual birds using GPS-trackers, several aspects of parental care (the number of food provisioning trips, home range size and nest attendance) could be quantified for different nesting phases. We found that in food-poor years, males spent less time near the nest, and had lower food provisioning rates during the incubation and nestling phases. In addition, males had larger home ranges in food-poor years, a possible indicator of increased foraging effort. In contrast, females increased their contribution to food provisioning in food-poor years, as shown by higher food provisioning rates and larger home ranges. This increased foraging effort came at the cost of lower nest attendance by females. Our data suggest that, when food abundance declines, Montagu’s Harriers shift from a system with almost strict sex-specific parental roles towards a system where both parents provide the same type of care with possibly increased sexual conflict

Increased food provisioning by female Montagu's Harriers in years with food shortage weakens sex-specific roles in parental care

n many owl and raptor species, sexes have distinct parental roles. Females incubate the eggs and raise the chicks until independence, while males provide females and their chicks with food. This is believed to reduce sexual conflict over parental care as tasks do not overlap. The level of parental care is also shaped by parent-offspring conflict. The scarcity of empirical data on parental investment in species with sex-specific parental roles was our motivation to study parental care in the Montagu’s Harrier Circus pygargus in relation to natural annual variation in food availability (vole abundance). By tracking individual birds using GPS-trackers, several aspects of parental care (the number of food provisioning trips, home range size and nest attendance) could be quantified for different nesting phases. We found that in food-poor years, males spent less time near the nest, and had lower food provisioning rates during the incubation and nestling phases. In addition, males had larger home ranges in food-poor years, a possible indicator of increased foraging effort. In contrast, females increased their contribution to food provisioning in food-poor years, as shown by higher food provisioning rates and larger home ranges. This increased foraging effort came at the cost of lower nest attendance by females. Our data suggest that, when food abundance declines, Montagu’s Harriers shift from a system with almost strict sex-specific parental roles towards a system where both parents provide the same type of care with possibly increased sexual conflict

Diet and foraging range of Slender-billed Gulls <i>Chroicocephalus genei</i> breeding in the Saloum Delta, Senegal

West African Slender-billed Gulls Chroicocephalus genei are considered vulnerable due to a very restricted breeding range. However, little information on their ecology is available to support conservation action. We describe diet and foraging range of Slender-billed Gulls breeding in the Saloum Delta National Park in Senegal. Diet was analysed on the basis of fish otoliths in excretion (mixture of pellets and faeces) collected near nests at the end of the incubation period between 2000 and 2015. Gulls mainly consumed fish of the families Cichlidae (25-93%), Clupeidae (0-54%) and Mugilidae (0-34%). The log-ratio proportion of Mugilidae increased significantly between 2000 and 2015, but there was no significant trend for other prey taxa. In 2014, UvA-BITS GPS-trackers were fitted to three Slender-billed Gulls to study movement and foraging range. During daytime, these gulls spent 27% of their time incubating the eggs, 10% elsewhere in the colony and 63% outside the colony on foraging trips. Foraging trips lasted on average 18 +/- 9.5 (+/- SD) hours. Total distance covered was on average 96 +/- 39 km with a maximum distance to the colony of 37 +/- 13 km. There were marked and consistent individual differences in the flight paths of the gulls. In two birds, foraging mainly took place in mangrove-bordered lagoons, salt pans, creeks, rivers and a complex of abandoned rice fields. The third bird almost exclusively explored the Atlantic coast near a fishing village in The Gambia. The home range and the foraging area of the three birds together measured 2400 and 1800 km(2), respectively. The diet components found near the nests of the three birds could only partly be related to their foraging areas

Rare case of an adult male Montagu's Harrier Circus pygargus over-summering in West Africa, as revealed by GPS tracking

Over-summering within or near the African wintering range by immature, non-breeding individuals occurs regularly in several species of long-distance migratory raptors, yet the extent of over-summering in Africa by adult birds remains unclear. In this study, we describe a case of an adult Montagu's Harrier over-summering in Africa, as revealed by GPS tracking. By relating detailed knowledge of the bird's movements to remotely sensed environmental data (normalized difference vegetation index, NDVI), we show that over-summering in this case was likely related to an exceptionally difficult breeding season the previous year rather than an effect of adverse weather conditions encountered during the winter or a failed attempt to migrate. Various factors are discussed as potential driving forces behind the bird's intra-African movements. Finally, we relate the documented case to a large number of North European Montagu's Harriers studied by telemetry and show that over-summering in Africa by adult individuals is indeed a rare event

Gps tracking data of western marsh harriers breeding in belgium and the Netherlands

In this data paper three datasets are described containing GPS tracking and acceleration data of Western marsh harriers (Circus aeruginosus) breeding in Belgium and the Netherlands. The Western marsh harrier is included as a threatened bird species in Annex I of the European Bird Directive due to the steep decline in population densities. In order to collect data of habitat use and migration behaviour, Western marsh harriers were equipped with light-weight solar powered GPS trackers developed by the Institute for Biodiversity and Ecosystem Dynamics (IBED) at the University of Amsterdam (University of Amsterdam Bird Tracking System, UvA-BiTS). These trackers automatically collect and store data on the bird’s activity and 3D position in time and transmit these data to ground stations. The datasets were collected by the Research Institute for Nature and Forest (INBO) and the Dutch Montagu’s Harrier Foundation. Tracked Western marsh harriers were breeding in the northeast of the Dutch province of Groningen and on the opposite side of the river Ems in Germany (H_GRONINGEN), in the region of Waterland-Oudeman near the Belgian-Dutch border (MH_WATERLAND), and at the left bank of the Scheldt estuary, close to the Belgian-Dutch border and north of the city of Antwerp (MH_ANTWERPEN). Most individuals remained within 10 km from their nesting sites during the breeding season and wintered in West Africa. H_GRONINGEN contains 987,493 GPS fixes and 3,853,859 acceleration records of four individuals since 2012. MH_WATERLAND contains 377,910 GPS fixes of seven individuals. Sampling in this region began in 2013. Three more Western marsh harriers were tagged in the Scheldt estuary near Antwerp more recently in 2018 (one individual) and 2019 (two individuals) for the MH_ANTWERPEN study, which contains 47,917 GPS fixes and 227,746 acceleration records. The three Western marsh harrier datasets were published as separate studies in Movebank (https://www. movebank.org) and archived as data packages in Zenodo (https://www.zenodo.org) to ensure long-term preservation and versioning of the data

A circannual perspective on daily and total flight distances in a long-distance migratory raptor, the Montagu’s harrier, Circus pygargus.

International audienceLong-distance migrants are particularly recognized for the distances coveredon migration, yet little is known about the distances they cover during therest of the year. GPS-tracks of 29 Montagu’s harriers from breeding areasin France, The Netherlands and Denmark showed that harriers fly between35 653 and 88 049 km yr21, of which on average only 28.5% is on migration.Mean daily distances during migration were 296 km d21 in autumn and252 km d21 in spring. Surprisingly, males’ daily distances during breeding(217 km d21) were close to those during migration, whereas breedingfemales moved significantly less (101 km d21) than males. In terms offlight distance, the breeding season seemed nearly as demanding asmigration periods for males. During the six winter months, both sexesmoved less (114 and 128 km d21 for females and males, respectively) thanduring migration. Harriers therefore covered shorter daily distances duringwinter which might allow birds to compensate for the more demandingphases of migration and breeding

First results of year-round tracking of Hen Harriers Circus cyaneus breeding in the agricultural landscape of East-Groningen

A small breeding population (3-5 pairs) of Hen Harriers recently established in the east of the province of Groningen, the Netherlands, in large scale arable farmland. We equipped three adults, two males and one female, with UvA-BiTS GPS loggers to study home ranges and habitat use throughout the year (Fig. 1). One breeding male could be tracked during two subsequent summers (late nestling phase in 2012, prebreeding and incubation phase in 2013 (Fig. 2)). Although he nested in the same area, he used different home ranges in these subsequent years (overlap only 21%). Habitat use was similar between years. Most time was spent in (winter) cereals (60%) and grassland (22%), two crops that dominate in the study area (availability is 42 and 24%, respectively). Moreover, set-aside habitats, which are especially created and managed for breeding harriers, were preferred (4% used, 1% available). One breeding pair was tracked after their nest failed (Fig. 4). These non-breeding birds occupied much smaller summer home ranges. In addition, they used set-aside habitat much more intensively (up to 22%), until the start of the cereal harvest when they switched to using cereal stubbles. During the summer the female made three subsequent trips to Northwest Germany (Fig. 3). One male spent the winter in Spain, in an agricultural area near Olivenza (Fig. 6). Autumn and spring migration took 98 and 14 days, including 81 and 1 stopover days, respectively. The other individuals (one male and one female) spent the winter near the breeding area (Fig. 5). Loggers could not record positions during mid-winter as solar panels could not keep the batteries charged. Habitat use in winter was dominated by grassland (62%). Set-aside was also preferred (5%). The female made an 8-day mid-winter excursion to a nearby wetland area (Weerribben, Fig. 5).</p