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

Home-ranges of tropical Red-capped Larks are influenced by breeding rather than vegetation, rainfall or invertebrate availability

Home-range studies have received considerable attention from ecologists but are greatly skewed towards the north temperate areas. Tropical areas offer an ideal setting to tease apart hypotheses about weather, food availability and social interactions as important factors influencing home-range. In this study, we investigated home-range and movement patterns of the tropical Red-capped Lark Callandrella cineria, a year-round breeding bird with a dynamic social structure. We tracked 56 individuals using radiotransmitters and colour-ring readings over a 23-month period. Our objective was to understand year-round variation in home-range size in the context of the highly aseasonal and unpredictable variation in weather and resources typical of many equatorial habitats, in addition to the birds? changing social structure and year-round breeding. The mean composite monthly home-range of Red-capped Larks was 58.0 ha, and the mean individual home-range size was 19.9 ha, but this varied considerably between individuals. The total number of nests found per month (breeding intensity) best predicted home-range size of non-breeding birds, and of breeding and non-breeding birds combined. We show for the first time that breeding intensity decreases the home-range size of non-breeding individuals. Our study also underlines the relevance of conducting more studies in aseasonal tropical areas in order to disentangle effects of weather, food availability and breeding that vary in parallel, peaking simultaneously in most seasonal areas

First geolocator tracks of Swedish red-necked phalaropes reveal the Scandinavia-Arabian Sea connection

We studied migration and wintering patterns of a wader with a pelagic lifestyle during the non-breeding period, the rednecked phalarope Phalaropus lobatus . Using light-level geolocation, we obtained three full annual tracks and one autumn migration track of male red-necked phalaropes caught during breeding in Scandinavia. Th ese tracks confi rmed expectations that individuals from the Scandinavian population winter in the Arabian Sea. Migration was accomplished in two to four migration leaps, staging for a few days in the Gulf of Finland (autumn) or the southern Baltic Sea (spring) and for up to a month in or near the Black and Caspian Sea (autumn and spring). In addition, travel speeds suggested that only the fl ights between the Baltic and Black/Caspian Sea are non-stop, and thus the birds seem to make additional short stops during the other flights. Stopover time in the Black/Caspian Sea is only 8 – 10 d in spring but up to 36 d in autumn, which is longer than expected if only used for pre-migratory fattening to cover the ca 2000 km to the Gulf of Oman. After entering the Arabian Sea via the Gulf of Oman, birds dispersed over the entire presumed winter range. Winter movements appear to correspond to the spatio-temporal patterns in primary production linked to seasonally changing monsoon winds. Th ese are not only the first tracks of Scandinavian red-necked phalaropes, but also the fi rst seabird tracks in the Arabian Sea, one of the most productive and dynamic marine areas on the planet

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

Individual migration patterns of Eurasian golden ploversPluvialis apricariabreeding in Swedish Lapland; examples of cold spell-induced winter movements

Tracking studies normally focus on long-distance migrants, meaning that our understanding about short-distance migration remains limited. In this study, we present the first individual tracks of the Eurasian golden plover Pluvialis apricaria, a short-distance migrant, which were tracked from a Scandinavian breeding population using geolocators. In addition, golden plovers are known for their cold spell-induced winter movements, and this study provides some first individual tracking data on this type of movements. In three cases the plovers spent the winter in NW Europe and in four cases they departed during winter from NW Europe to spend the rest of the winter in Iberia or Morocco (one bird that was tracked during two subsequent migration cycles moved to Iberia in the first winter but remained in NW Europe during the second winter). The four winter departures were associated with a cold spell in NW Europe during which maximum temperatures dropped to freezing. Cold spell-induced winter movements were notably long and fast. The birds that remained at their NW European wintering site did not experience such cold spell. Interestingly, the individual that was tracked for a second season did experience four cold spells at its wintering site in NW France, but it never left this area, indicating that plovers not always move on in response to cold. Little information was obtained about spring migration, but one bird had a prominent counter-clockwise loop migration pattern through E Europe. Due to their cold spell winter movements, golden plovers exhibit great flexibility in migration patterns, resulting in a notably large spread in final wintering areas