The conservation of Eurasian Curlews, whose numbers are declining, is aided through an understanding of environmental challenges faced by the birds throughout the annual cycle. In the Moray Firth, northern Scotland, 48 non-breeding Curlews were tagged with geolocators to describe their migrations (routes, destinations and timing), time of breeding and nest success. Based on 19 recaptures, breeding destinations included northern Scotland (21% of tagged birds), Norway (32%), Sweden (21%) and Finland plus Russia (26%). These percentages matched closely with the results from earlier ringing recoveries/sightings. The median last date in the non-breeding area varied for the Fennoscandian birds: 31 March for those migrating to Norway, 11 April for Swedish birds and 15 April for Finnish birds. The amount of migratory fuel accumulated prior to departure in early April was 10–13% of the late winter mass, sufficient for a 1000-km flight, which was similar to the median distance to Norwegian, but not Swedish or Finnish, destinations. Staging en route characterised the migrations to these latter destinations, resulting in longer migration times. Most of the Fennoscandian Curlews migrated across the North Sea with a tailwind component in spring, but all had a headwind component in autumn. A first-year bird remained in northern Scotland for the first summer, but migrated to Russia in the second and did not nest. Arrival on the breeding grounds varied significantly according to destination. Males and females incubated at different parts of the 24-hour cycle, even although there were 24 hours of daylight for most birds. Of birds that nested, 63% hatched clutches, some after a second attempt. Periods of 24 hours of daylight masked the initial departure from the breeding grounds, so only the latter part of the autumn migration and first date back at the non-breeding area were recorded (11 July), with no difference among the Fennoscandian breeding birds.
{"title":"Migrations, Destinations and Breeding of Eurasian Curlews Numenius arquata arquata that Spend the Non-Breeding Season in Northern Scotland","authors":"R.W. Summers, R.L. Swann, B. Etheridge, N. Elkins","doi":"10.5253/arde.2023.a8","DOIUrl":"https://doi.org/10.5253/arde.2023.a8","url":null,"abstract":"The conservation of Eurasian Curlews, whose numbers are declining, is aided through an understanding of environmental challenges faced by the birds throughout the annual cycle. In the Moray Firth, northern Scotland, 48 non-breeding Curlews were tagged with geolocators to describe their migrations (routes, destinations and timing), time of breeding and nest success. Based on 19 recaptures, breeding destinations included northern Scotland (21% of tagged birds), Norway (32%), Sweden (21%) and Finland plus Russia (26%). These percentages matched closely with the results from earlier ringing recoveries/sightings. The median last date in the non-breeding area varied for the Fennoscandian birds: 31 March for those migrating to Norway, 11 April for Swedish birds and 15 April for Finnish birds. The amount of migratory fuel accumulated prior to departure in early April was 10–13% of the late winter mass, sufficient for a 1000-km flight, which was similar to the median distance to Norwegian, but not Swedish or Finnish, destinations. Staging en route characterised the migrations to these latter destinations, resulting in longer migration times. Most of the Fennoscandian Curlews migrated across the North Sea with a tailwind component in spring, but all had a headwind component in autumn. A first-year bird remained in northern Scotland for the first summer, but migrated to Russia in the second and did not nest. Arrival on the breeding grounds varied significantly according to destination. Males and females incubated at different parts of the 24-hour cycle, even although there were 24 hours of daylight for most birds. Of birds that nested, 63% hatched clutches, some after a second attempt. Periods of 24 hours of daylight masked the initial departure from the breeding grounds, so only the latter part of the autumn migration and first date back at the non-breeding area were recorded (11 July), with no difference among the Fennoscandian breeding birds.","PeriodicalId":55463,"journal":{"name":"Ardea","volume":"37 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-10-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"136012932","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"生物学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Seabirds have long lives, reproduce slowly and usually do not attempt to relay within the same breeding season after nest failure. In Sandwich Terns Thalasseus sandvicensis, renesting has never been documented despite the large number of studies on their breeding ecology and recorded prospecting behaviour after nest failure. In 2020, we observed how three GPS-tagged Sandwich Terns moved 115 km after nest failure for a second breeding attempt. One of these birds hatched a chick from the second clutch successfully. We hypothesize that synchronous breeding usually prevents Sandwich Terns from trying again after nest failure and that the relays observed in 2020 were facilitated by the unusual situation of a successful breeding colony that started three weeks later than all other colonies in the Netherlands.
{"title":"Second Breeding Attempts of Sandwich Terns in a Different Colony: Facilitated by Breeding Asynchrony between Colonies?","authors":"Ruben C. Fijn, Rob S.A. van Bemmelen","doi":"10.5253/arde.2022.a32","DOIUrl":"https://doi.org/10.5253/arde.2022.a32","url":null,"abstract":"Seabirds have long lives, reproduce slowly and usually do not attempt to relay within the same breeding season after nest failure. In Sandwich Terns Thalasseus sandvicensis, renesting has never been documented despite the large number of studies on their breeding ecology and recorded prospecting behaviour after nest failure. In 2020, we observed how three GPS-tagged Sandwich Terns moved 115 km after nest failure for a second breeding attempt. One of these birds hatched a chick from the second clutch successfully. We hypothesize that synchronous breeding usually prevents Sandwich Terns from trying again after nest failure and that the relays observed in 2020 were facilitated by the unusual situation of a successful breeding colony that started three weeks later than all other colonies in the Netherlands.","PeriodicalId":55463,"journal":{"name":"Ardea","volume":"22 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-10-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135969914","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"生物学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
{"title":"Ornithology from the Tree Tops Woodland Raptors are Declining and have Fallen Silent: Is It Pesticides, Again?","authors":"Rob G. Bijlsma","doi":"10.5253/arde.2023.a14","DOIUrl":"https://doi.org/10.5253/arde.2023.a14","url":null,"abstract":"","PeriodicalId":55463,"journal":{"name":"Ardea","volume":"112 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-10-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135969894","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"生物学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Kees (C.J.) Camphuysen, Susanne C. van Donk, Judy Shamoun-Baranes, Rosemarie Kentie
The population increase of Lesser Black-backed Gulls in The Netherlands triggered investigations into life-history, migratory movements and foraging ecology during 16 years of nest-monitoring, colour-ringing and GPS-tracking on the island of Texel (Wadden Sea). The main objective was to obtain comprehensive ecological data on breeding performance within the context of the annual cycle, shifts in resources, prey types and habitat use. Migration strategies ranged from short- (France, England), medium- (Portugal, Spain) to long-distance (NW Africa), utilising marine, coastal or terrestrial, region-specific resources. Young birds travelled on average further than older individuals. Strong within-colony philopatry was found, this was strongest in males. Assessments of mate-fidelity indicated serial, social monogamy. Unexpectedly, given increasing population trends when the study commenced, fledging rates were low and declining egg volumes, smaller hatchlings, declining mass at fledging and high levels of cannibalism indicated structural food stress. Fledgling mass was well below that of chicks in historical studies, suggesting insufficient provisioning. Breeding was highly synchronised and early nesters fledged more young than late pairs. The onset of breeding was significantly delayed over the years, chick depredation rates declined, overall breeding success became more variable. Marine, urban and rural habitats, mostly within 80 km from the colony were used for foraging. Marine prey, mostly fisheries discards, formed the principal prey for most birds, supplemented with food found in agricultural areas. Human waste was found in only 7% of prey samples. A consistent decline of marine prey (in line with developing restrictions in fisheries), combined with signals pointing at food stress, suggests that the population is unable to boost reproductive success with currently existing foraging opportunities.
{"title":"The Annual Cycle, Breeding Biology and Feeding Ecology of the Lesser Black-Backed Gull Larus fuscus","authors":"Kees (C.J.) Camphuysen, Susanne C. van Donk, Judy Shamoun-Baranes, Rosemarie Kentie","doi":"10.5253/arde.2023.a7","DOIUrl":"https://doi.org/10.5253/arde.2023.a7","url":null,"abstract":"The population increase of Lesser Black-backed Gulls in The Netherlands triggered investigations into life-history, migratory movements and foraging ecology during 16 years of nest-monitoring, colour-ringing and GPS-tracking on the island of Texel (Wadden Sea). The main objective was to obtain comprehensive ecological data on breeding performance within the context of the annual cycle, shifts in resources, prey types and habitat use. Migration strategies ranged from short- (France, England), medium- (Portugal, Spain) to long-distance (NW Africa), utilising marine, coastal or terrestrial, region-specific resources. Young birds travelled on average further than older individuals. Strong within-colony philopatry was found, this was strongest in males. Assessments of mate-fidelity indicated serial, social monogamy. Unexpectedly, given increasing population trends when the study commenced, fledging rates were low and declining egg volumes, smaller hatchlings, declining mass at fledging and high levels of cannibalism indicated structural food stress. Fledgling mass was well below that of chicks in historical studies, suggesting insufficient provisioning. Breeding was highly synchronised and early nesters fledged more young than late pairs. The onset of breeding was significantly delayed over the years, chick depredation rates declined, overall breeding success became more variable. Marine, urban and rural habitats, mostly within 80 km from the colony were used for foraging. Marine prey, mostly fisheries discards, formed the principal prey for most birds, supplemented with food found in agricultural areas. Human waste was found in only 7% of prey samples. A consistent decline of marine prey (in line with developing restrictions in fisheries), combined with signals pointing at food stress, suggests that the population is unable to boost reproductive success with currently existing foraging opportunities.","PeriodicalId":55463,"journal":{"name":"Ardea","volume":"28 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-10-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135549196","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"生物学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Many migratory bird species cross the Mediterranean during autumn migration, but most do so either at the western or eastern ends where they can avoid, or minimise, sea crossings. The intervening 3500 km has long sea crossings, probably adding to the barrier imposed by the Sahara. If this were the general migration pattern, it would result in high concentrations of Afro-Palearctic migrants in West and East Africa and fewer in the central sub-Saharan zones. Unless migrants reorientate upon reaching the sub-Sahara, densities of migratory birds in the central Sahel should be much lower than at either end of the African savannah range. The available studies of birds equipped with GPS or geolocators show that south of the Sahara at least some species perform lateral movements to some extent. However, many remain either in the Sahel's western or eastern parts or continue moving southwards along the same longitudinal axis. We use density counts of arboreal birds from across the full width of the Sahel to explore the extent to which the central Sahel zone is underused by migratory birds. Eleven out of twelve common migratory arboreal species occurred at lower densities in the central Sahel than could be explained by tree-related variables. Western Bonelli's Warbler Phylloscopus bonelli, Western Orphean Warbler Curruca hortensis and Subalpine Warbler Curruca cantillans were most common in the western and (much) less common in the central Sahel, whereas Eastern Olivaceous Warbler Iduna pallida, Eastern Orphean Warbler Curruca crassirostris, Lesser Whitethroat Curruca curruca and Rüppell's Warbler Curruca ruppeli were most common in eastern, but less so in the central Sahel. Woodchat Shrike Lanius senator and Common Redstart Phoenicurus phoenicurus were more common in the western and eastern parts than in the central Sahel. No longitudinal variation was found for Common Whitethroat Curruca communis, which is consistent with the knowledge that many cross the Mediterranean waters upon encountering them. The conclusion is justified that the central Sahel is underused by migratory birds and by consequence, as far as these birds are concerned, not ‘saturated’. The question arises whether in the past, when the number of migratory birds was much greater than today, there might not have been a Gap of Chad.
{"title":"The Gap of Chad, a Dearth of Migratory Birds in the Central Sahel","authors":"L. Zwarts, R. Bijlsma, J. Kamp","doi":"10.5253/arde.2022.a22","DOIUrl":"https://doi.org/10.5253/arde.2022.a22","url":null,"abstract":"Many migratory bird species cross the Mediterranean during autumn migration, but most do so either at the western or eastern ends where they can avoid, or minimise, sea crossings. The intervening 3500 km has long sea crossings, probably adding to the barrier imposed by the Sahara. If this were the general migration pattern, it would result in high concentrations of Afro-Palearctic migrants in West and East Africa and fewer in the central sub-Saharan zones. Unless migrants reorientate upon reaching the sub-Sahara, densities of migratory birds in the central Sahel should be much lower than at either end of the African savannah range. The available studies of birds equipped with GPS or geolocators show that south of the Sahara at least some species perform lateral movements to some extent. However, many remain either in the Sahel's western or eastern parts or continue moving southwards along the same longitudinal axis. We use density counts of arboreal birds from across the full width of the Sahel to explore the extent to which the central Sahel zone is underused by migratory birds. Eleven out of twelve common migratory arboreal species occurred at lower densities in the central Sahel than could be explained by tree-related variables. Western Bonelli's Warbler Phylloscopus bonelli, Western Orphean Warbler Curruca hortensis and Subalpine Warbler Curruca cantillans were most common in the western and (much) less common in the central Sahel, whereas Eastern Olivaceous Warbler Iduna pallida, Eastern Orphean Warbler Curruca crassirostris, Lesser Whitethroat Curruca curruca and Rüppell's Warbler Curruca ruppeli were most common in eastern, but less so in the central Sahel. Woodchat Shrike Lanius senator and Common Redstart Phoenicurus phoenicurus were more common in the western and eastern parts than in the central Sahel. No longitudinal variation was found for Common Whitethroat Curruca communis, which is consistent with the knowledge that many cross the Mediterranean waters upon encountering them. The conclusion is justified that the central Sahel is underused by migratory birds and by consequence, as far as these birds are concerned, not ‘saturated’. The question arises whether in the past, when the number of migratory birds was much greater than today, there might not have been a Gap of Chad.","PeriodicalId":55463,"journal":{"name":"Ardea","volume":"111 1","pages":"207 - 226"},"PeriodicalIF":0.4,"publicationDate":"2023-07-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"44303028","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"生物学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Bird counts in the Ferlo, NW Senegal had shown that the density of ground-foraging birds was much lower in grazed than in ungrazed savannah: 84% fewer granivorous birds and 64% fewer insectivorous birds. Between 1960 and 2010, in three areas within the same region, granivores declined by 39–97% and insectivores by 61–91%, losses attributable to the steadily increasing livestock grazing pressure. If these trends hold for all Sahelian rangelands, the extrapolation at the time indicated that 1.5 billion birds would have been lost in just half a century. The aim of this space-for-time substitution study was to investigate whether that extrapolation can be substantiated with data from the eastern Sahel. To permit analysis of the spatial and seasonal variation in grazing pressure and its impact on ground-foraging granivorous and insectivorous birds, we counted birds in 1901 sites across the entire region (Mauritania to Ethiopia) and took landscape photos of these sites to evaluate livestock presence. We also estimated livestock density from our counts of cowpats and of droppings of sheep and goats, and the cover of the soil vegetation. Within the same rainfall zone (200–400 mm/year), the grazing pressure was higher in the Ferlo than elsewhere in the Sahel. Grazing pressure declined in the Ferlo in the course of the dry season, indicating that cattle food supply became depleted. No such seasonal decline was recorded elsewhere in the Sahel. The same pattern was found for ground-foraging birds: a decline during the dry season in the Ferlo, but nowhere else in the same Sahel rainfall zone. Indeed, in the 1960s and 1970s, when the grazing pressure was much lower than today, there were no records of a seasonal decline of ground-foraging birds in the Ferlo. The much lower densities of seed-eating birds in the Ferlo were not exhibited elsewhere in the Sahel, which is consistent with the phenomenon of local overgrazing. The previous extrapolated loss of 1.5 billion birds is therefore too high, because conditions in the Ferlo were found to differ from those experienced elsewhere in Sahel's arid zone. The actual overall loss cannot be specified due to lack of bird counts from the past in the eastern Sahel. The comparison of grazing pressure and bird densities across all rainfall zones of the western and eastern Sahel shows that increasing livestock densities negatively impact bird numbers. Livestock grazing pressure in the west was higher than in the east and most ground-foraging bird species were less common in the west than in the east. Furthermore, the majority of ground-foraging species in West Sahelian savannahs were exclusively confined to the arid and semi-arid zone, but in the east, these species were more widely distributed and also occupied the more humid zone to the south.
{"title":"Downstream Ecological Consequences of Livestock Grazing in the Sahel: A Space-For-Time Analysis of the Relations between Livestock and Birds","authors":"L. Zwarts, R. Bijlsma, J. Kamp","doi":"10.5253/arde.2022.a25","DOIUrl":"https://doi.org/10.5253/arde.2022.a25","url":null,"abstract":"Bird counts in the Ferlo, NW Senegal had shown that the density of ground-foraging birds was much lower in grazed than in ungrazed savannah: 84% fewer granivorous birds and 64% fewer insectivorous birds. Between 1960 and 2010, in three areas within the same region, granivores declined by 39–97% and insectivores by 61–91%, losses attributable to the steadily increasing livestock grazing pressure. If these trends hold for all Sahelian rangelands, the extrapolation at the time indicated that 1.5 billion birds would have been lost in just half a century. The aim of this space-for-time substitution study was to investigate whether that extrapolation can be substantiated with data from the eastern Sahel. To permit analysis of the spatial and seasonal variation in grazing pressure and its impact on ground-foraging granivorous and insectivorous birds, we counted birds in 1901 sites across the entire region (Mauritania to Ethiopia) and took landscape photos of these sites to evaluate livestock presence. We also estimated livestock density from our counts of cowpats and of droppings of sheep and goats, and the cover of the soil vegetation. Within the same rainfall zone (200–400 mm/year), the grazing pressure was higher in the Ferlo than elsewhere in the Sahel. Grazing pressure declined in the Ferlo in the course of the dry season, indicating that cattle food supply became depleted. No such seasonal decline was recorded elsewhere in the Sahel. The same pattern was found for ground-foraging birds: a decline during the dry season in the Ferlo, but nowhere else in the same Sahel rainfall zone. Indeed, in the 1960s and 1970s, when the grazing pressure was much lower than today, there were no records of a seasonal decline of ground-foraging birds in the Ferlo. The much lower densities of seed-eating birds in the Ferlo were not exhibited elsewhere in the Sahel, which is consistent with the phenomenon of local overgrazing. The previous extrapolated loss of 1.5 billion birds is therefore too high, because conditions in the Ferlo were found to differ from those experienced elsewhere in Sahel's arid zone. The actual overall loss cannot be specified due to lack of bird counts from the past in the eastern Sahel. The comparison of grazing pressure and bird densities across all rainfall zones of the western and eastern Sahel shows that increasing livestock densities negatively impact bird numbers. Livestock grazing pressure in the west was higher than in the east and most ground-foraging bird species were less common in the west than in the east. Furthermore, the majority of ground-foraging species in West Sahelian savannahs were exclusively confined to the arid and semi-arid zone, but in the east, these species were more widely distributed and also occupied the more humid zone to the south.","PeriodicalId":55463,"journal":{"name":"Ardea","volume":"111 1","pages":"269 - 282"},"PeriodicalIF":0.4,"publicationDate":"2023-07-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"48805276","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"生物学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
A. Schlaich, V. Bretagnolle, C. Both, B. Koks, R. Klaassen
Palearctic migrants wintering in Africa commonly use several sites throughout the winter, a strategy known as ‘itinerancy’. In this way, migrants track spatiotemporal variation in resources. Despite the importance of this strategy for migratory landbirds, we still lack detailed understanding of how variation in environmental conditions affects site use and the timing of movements between sites. We tracked 125 adult Montagu’s Harriers Circus pygargus from Western European breeding populations between 2005 and 2018 using satellite transmitters and GPS trackers. In total, data on 129 complete wintering seasons were obtained, including 33 individuals that were followed in two or more winters. Montagu’s Harriers were itinerant, using on average 3.3 wintering sites, to which they showed high site fidelity between years. The first sites harriers used after arriving in their wintering range were situated in the northern Sahel and were dominated by natural and sparse vegetation. Subsequent sites, situated further south in the Sahel, were mainly dominated by agricultural and natural habitats. Sites used by harriers had higher habitat diversity compared to random sites. Home range size and activity (time flying per day, daily distance) peaked at the last sites harriers used (i.e. the site from which they commenced spring migration). For individuals tracked in multiple seasons, we showed that home range size did not depend on vegetation greenness. However, the birds covered longer daily distances at the same site in drier years compared to greener (wetter) years. Importantly, the timing of the movements between wintering sites was affected by local environmental conditions, with individuals staying for shorter durations and departing earlier from first sites in drier years and arriving earlier at last sites in greener years. We conclude that within the context of a strategy of itinerancy, Montagu’s Harriers are faithful to the sites they use between years (spatial component), but flexible in the timing of use of these sites (temporal component), which they adjust to annual variation in environmental conditions.
{"title":"On the Wintering Ecology of Montagu's Harriers in West Africa: Itinerancy in Relation to Varying Annual Environmental Conditions","authors":"A. Schlaich, V. Bretagnolle, C. Both, B. Koks, R. Klaassen","doi":"10.5253/arde.2023.a4","DOIUrl":"https://doi.org/10.5253/arde.2023.a4","url":null,"abstract":"Palearctic migrants wintering in Africa commonly use several sites throughout the winter, a strategy known as ‘itinerancy’. In this way, migrants track spatiotemporal variation in resources. Despite the importance of this strategy for migratory landbirds, we still lack detailed understanding of how variation in environmental conditions affects site use and the timing of movements between sites. We tracked 125 adult Montagu’s Harriers Circus pygargus from Western European breeding populations between 2005 and 2018 using satellite transmitters and GPS trackers. In total, data on 129 complete wintering seasons were obtained, including 33 individuals that were followed in two or more winters. Montagu’s Harriers were itinerant, using on average 3.3 wintering sites, to which they showed high site fidelity between years. The first sites harriers used after arriving in their wintering range were situated in the northern Sahel and were dominated by natural and sparse vegetation. Subsequent sites, situated further south in the Sahel, were mainly dominated by agricultural and natural habitats. Sites used by harriers had higher habitat diversity compared to random sites. Home range size and activity (time flying per day, daily distance) peaked at the last sites harriers used (i.e. the site from which they commenced spring migration). For individuals tracked in multiple seasons, we showed that home range size did not depend on vegetation greenness. However, the birds covered longer daily distances at the same site in drier years compared to greener (wetter) years. Importantly, the timing of the movements between wintering sites was affected by local environmental conditions, with individuals staying for shorter durations and departing earlier from first sites in drier years and arriving earlier at last sites in greener years. We conclude that within the context of a strategy of itinerancy, Montagu’s Harriers are faithful to the sites they use between years (spatial component), but flexible in the timing of use of these sites (temporal component), which they adjust to annual variation in environmental conditions.","PeriodicalId":55463,"journal":{"name":"Ardea","volume":"111 1","pages":"321 - 342"},"PeriodicalIF":0.4,"publicationDate":"2023-07-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"46389737","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"生物学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
This paper quantifies the density and the total number of granivorous and insectivorous ground-foraging birds, whether Afro-Palearctic migrants or Afro-tropical residents, in the transition zone between the arid Sahara and the humid Guinea zone. Situated between 17°W and 42°E and between 7°N and 22°N, this is an area covering 10 million km2. The study took place during the northern winter, between 20 November and 10 March (thus covering much of the long dry season) from 2011 up to and including 2019. Using a stratified random sampling regime, we counted birds at 1901 sites of 4.5 ha in area. We present background information about the study region, with maps showing variation in elevation, rainfall, woody cover, land use and human population density. The bird counts were converted into average densities for 43 bird species in 150 grid cells of 1° latitude × 1° longitude. The distribution of the various bird species was predominantly related to annual rainfall, but because woody cover increases with rainfall, species' preferences for arid or more humid zones were partly influenced by an overall preference for open or more wooded landscapes. Bird species such as larks and Tawny Pipit Anthus campestris, even when rainfall was accounted for, selected comparatively open landscapes, whereas species feeding on the ground near trees or using them as perches (e.g. sparrows, finches, shrikes, Tree Pipit Anthus trivialis) preferred relatively more enclosed environments. To estimate total population size, the 150 grid cells were assembled into eleven rainfall categories (per 100 mm rainfall) and six longitudinal bands. To assess the reliability of these estimations, population sizes were calculated separately on the 1901 study sites split in two halves. The estimated population sizes were precise for migrants, especially for insectivores (7% deviation for the split-half estimates), but less precise for residents (22–28% deviation). Most ground-foraging birds were granivorous (at least in the dry season), their total number being estimated at 4000 million residents and 133 million migrants, residents being 30 times as abundant as migrants. Ground-foraging insectivores were less numerous, the total estimated being 920 million birds, of which 694 million were residents and 221 million migrants, the ratio residents/migrants being an order of magnitude smaller than in granivores. The three most abundant granivorous residents were Red-cheeked Cordon-bleu Uraeginthus bengalus (467 million), Sudan Golden Sparrow Passer luteus (375 million birds) and Red-billed Quelea Quelea quelea (311 million). The Greater Short-toed Lark Calandrella brachydactyla (126 million) was the only common granivorous migrant. The most common insectivorous ground-foraging bird was a resident (Greater Blue-eared Starling Lamprotornis chalybaeus; 100 million), and more commonly encountered than all the ground-foraging insectivorous migrants such as Isabelline Wheatear Oenanthe isabellina (32
{"title":"Distribution and Numbers of Ground-Foraging Birds between the Hyper-Arid Sahara and the Hyper-Humid Guinea Forests","authors":"L. Zwarts, R. Bijlsma, J. D. Kamp, Marten Sikkema","doi":"10.5253/arde.2022.a16","DOIUrl":"https://doi.org/10.5253/arde.2022.a16","url":null,"abstract":"This paper quantifies the density and the total number of granivorous and insectivorous ground-foraging birds, whether Afro-Palearctic migrants or Afro-tropical residents, in the transition zone between the arid Sahara and the humid Guinea zone. Situated between 17°W and 42°E and between 7°N and 22°N, this is an area covering 10 million km2. The study took place during the northern winter, between 20 November and 10 March (thus covering much of the long dry season) from 2011 up to and including 2019. Using a stratified random sampling regime, we counted birds at 1901 sites of 4.5 ha in area. We present background information about the study region, with maps showing variation in elevation, rainfall, woody cover, land use and human population density. The bird counts were converted into average densities for 43 bird species in 150 grid cells of 1° latitude × 1° longitude. The distribution of the various bird species was predominantly related to annual rainfall, but because woody cover increases with rainfall, species' preferences for arid or more humid zones were partly influenced by an overall preference for open or more wooded landscapes. Bird species such as larks and Tawny Pipit Anthus campestris, even when rainfall was accounted for, selected comparatively open landscapes, whereas species feeding on the ground near trees or using them as perches (e.g. sparrows, finches, shrikes, Tree Pipit Anthus trivialis) preferred relatively more enclosed environments. To estimate total population size, the 150 grid cells were assembled into eleven rainfall categories (per 100 mm rainfall) and six longitudinal bands. To assess the reliability of these estimations, population sizes were calculated separately on the 1901 study sites split in two halves. The estimated population sizes were precise for migrants, especially for insectivores (7% deviation for the split-half estimates), but less precise for residents (22–28% deviation). Most ground-foraging birds were granivorous (at least in the dry season), their total number being estimated at 4000 million residents and 133 million migrants, residents being 30 times as abundant as migrants. Ground-foraging insectivores were less numerous, the total estimated being 920 million birds, of which 694 million were residents and 221 million migrants, the ratio residents/migrants being an order of magnitude smaller than in granivores. The three most abundant granivorous residents were Red-cheeked Cordon-bleu Uraeginthus bengalus (467 million), Sudan Golden Sparrow Passer luteus (375 million birds) and Red-billed Quelea Quelea quelea (311 million). The Greater Short-toed Lark Calandrella brachydactyla (126 million) was the only common granivorous migrant. The most common insectivorous ground-foraging bird was a resident (Greater Blue-eared Starling Lamprotornis chalybaeus; 100 million), and more commonly encountered than all the ground-foraging insectivorous migrants such as Isabelline Wheatear Oenanthe isabellina (32 ","PeriodicalId":55463,"journal":{"name":"Ardea","volume":"111 1","pages":"7 - 66"},"PeriodicalIF":0.4,"publicationDate":"2023-07-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"47535037","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"生物学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Every year, hundreds of millions of migratory birds cross the Sahara to spend the northern winter in the Sahel. After their arrival in September the region does not receive any rainfall until June while temperatures increase. Birds inhabiting the Sahel have several strategies to cope with this seasonal advent of drought. Most ground-foraging and arboreal migrants actually remain in the desiccating Sahel, although Northern Wheatear Oenanthe oenanthe remains in the arid zone only in a wet year, but moves from the arid to the semi-arid zone in a dry year. Some arboreal migrants stay for 1–2 months in the Sahel during the early dry season, but move on to the more humid zone further south for the rest of the northern winter. Common Redstart Phoenicurus phoenicurus is the only Sahelian arboreal migrant that moves southward in this period. Counter-intuitively, Curruca species move northward after the early dry season to the arid zone where they concentrate in woody plant species whose attractiveness increases later in the dry season. This is either because those plants then gain berries (Toothbrush Tree Salvadora persica) or because they develop flowers (six desert species). In the semi-arid zone, tree-dwelling bird species disappear from tree species when these lose their leaves. However, in tree species which do not shed their leaves, bird numbers remain either constant (those using Desert Date Balanites aegyptiaca) or increase (those using Winter Thorn Faidherbia albida, a tree that foliates during the dry season). On floodplains bird numbers in acacia trees increase during the dry season. As a consequence, birds become concentrated in fewer tree and shrub species during their stay in the Sahel. After wet rainy seasons, trees have more flowers and leaves and shed them later, giving the birds more foraging space. At the end of their stay in Africa after dry rainy seasons, the number of arboreal birds is only half that after wet rainy seasons, suggesting higher mortality in dry years. Clearly, in such years mortality would be even higher without what can be seen as ‘refuge trees’: the acacias on floodplains, and Faidherbia and to a lesser degree Balanites in the rest of the Sahel.
{"title":"Seasonal Shifts in Habitat Choice of Birds in the Sahel and the Importance of ‘Refuge Trees’ for Surviving the Dry Season","authors":"L. Zwarts, R. Bijlsma, J. Kamp","doi":"10.5253/arde.2022.a23","DOIUrl":"https://doi.org/10.5253/arde.2022.a23","url":null,"abstract":"Every year, hundreds of millions of migratory birds cross the Sahara to spend the northern winter in the Sahel. After their arrival in September the region does not receive any rainfall until June while temperatures increase. Birds inhabiting the Sahel have several strategies to cope with this seasonal advent of drought. Most ground-foraging and arboreal migrants actually remain in the desiccating Sahel, although Northern Wheatear Oenanthe oenanthe remains in the arid zone only in a wet year, but moves from the arid to the semi-arid zone in a dry year. Some arboreal migrants stay for 1–2 months in the Sahel during the early dry season, but move on to the more humid zone further south for the rest of the northern winter. Common Redstart Phoenicurus phoenicurus is the only Sahelian arboreal migrant that moves southward in this period. Counter-intuitively, Curruca species move northward after the early dry season to the arid zone where they concentrate in woody plant species whose attractiveness increases later in the dry season. This is either because those plants then gain berries (Toothbrush Tree Salvadora persica) or because they develop flowers (six desert species). In the semi-arid zone, tree-dwelling bird species disappear from tree species when these lose their leaves. However, in tree species which do not shed their leaves, bird numbers remain either constant (those using Desert Date Balanites aegyptiaca) or increase (those using Winter Thorn Faidherbia albida, a tree that foliates during the dry season). On floodplains bird numbers in acacia trees increase during the dry season. As a consequence, birds become concentrated in fewer tree and shrub species during their stay in the Sahel. After wet rainy seasons, trees have more flowers and leaves and shed them later, giving the birds more foraging space. At the end of their stay in Africa after dry rainy seasons, the number of arboreal birds is only half that after wet rainy seasons, suggesting higher mortality in dry years. Clearly, in such years mortality would be even higher without what can be seen as ‘refuge trees’: the acacias on floodplains, and Faidherbia and to a lesser degree Balanites in the rest of the Sahel.","PeriodicalId":55463,"journal":{"name":"Ardea","volume":"111 1","pages":"227 - 250"},"PeriodicalIF":0.4,"publicationDate":"2023-07-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"43431590","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"生物学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The Sahel is thinly covered by trees, but nevertheless forms an important habitat for millions of tree-dwelling birds. We describe tree availability and tree selection of 14 insectivorous Afro-Palearctic migrants and 18 Afro-tropical residents (10 insectivores, 3 frugivores and 5 nectarivores) inhabiting the Sahel from the Atlantic to the Red Sea. Of the 304 woody species identified across the region during systematic fieldwork in stratified plots, we noted height and canopy surface of 760,000 individual woody plants. Birds present in trees and shrubs were recorded separately per individual woody plant. 99.5% of the birds were concentrated in only 41 woody species. For 20 out of 32 bird species, Winter Thorn Faidherbia albida was the tree species most often used. Two other important tree species were Umbrella Thorn Acacia tortilis and Desert Date Balanites aegyptiaca. Representing only 11% of the total woody canopy cover, these three species attracted 89% of Western Bonelli's Warblers Phylloscopus bonelli and 77% of Subalpine Warblers Curruca iberiae + subalpina + cantillans. High selectivity for particular woody species was typical for migrants and residents, irrespective of their diet. Bird species feeding in shrubs used a larger variety of woody species than bird species feeding in tall trees. The highest bird densities (80–160 birds/ha canopy) were found in three shrubs with a limited distribution in the southern Sahara and northern Sahel: the berry-bearing Toothbrush Tree Salvadora persica, the small thorny shrub Sodad Capparis decidua and the small tree Maerua crassifolia. Other bird-rich woody species were without exception thorny (Balanites aegyptiaca, various species of acacia and ziziphus). In contrast, the five woody species most commonly distributed across the region (Cashew Anacardium occidentale, African Birch Anogeissus leiocarpus, Combretum glutinosum, Guiera senegalensis and Shea Tree Vitellaria paradoxa), representing 27% of the woody cover in the study sites, were rarely visited by foraging birds. In this sub-Saharan region, it is not total woody cover per se that matters to birds, but the presence of specific woody species. This finding has important implications: remote sensing studies showing global increase or decline of woody vegetation without identifying individual species have little value in explaining trends in arboreal bird populations. Local people have a large impact on the species composition of the woody vegetation in the Sahel, with positive and negative consequences for migrants wintering in this region. Faidherbia albida, the most important tree for birds in the sub-Saharan dry belt, is highly valued by local people and has the distinction of leafing in winter and being attractive to arthropods. On the other hand, migratory and African bird species have been negatively affected by the rapidly expanding cashew plantations since the early 1980s.
{"title":"Selection by Birds of Shrub and Tree Species in the Sahel","authors":"L. Zwarts, R. Bijlsma, J. D. Kamp","doi":"10.5253/arde.2022.a20","DOIUrl":"https://doi.org/10.5253/arde.2022.a20","url":null,"abstract":"The Sahel is thinly covered by trees, but nevertheless forms an important habitat for millions of tree-dwelling birds. We describe tree availability and tree selection of 14 insectivorous Afro-Palearctic migrants and 18 Afro-tropical residents (10 insectivores, 3 frugivores and 5 nectarivores) inhabiting the Sahel from the Atlantic to the Red Sea. Of the 304 woody species identified across the region during systematic fieldwork in stratified plots, we noted height and canopy surface of 760,000 individual woody plants. Birds present in trees and shrubs were recorded separately per individual woody plant. 99.5% of the birds were concentrated in only 41 woody species. For 20 out of 32 bird species, Winter Thorn Faidherbia albida was the tree species most often used. Two other important tree species were Umbrella Thorn Acacia tortilis and Desert Date Balanites aegyptiaca. Representing only 11% of the total woody canopy cover, these three species attracted 89% of Western Bonelli's Warblers Phylloscopus bonelli and 77% of Subalpine Warblers Curruca iberiae + subalpina + cantillans. High selectivity for particular woody species was typical for migrants and residents, irrespective of their diet. Bird species feeding in shrubs used a larger variety of woody species than bird species feeding in tall trees. The highest bird densities (80–160 birds/ha canopy) were found in three shrubs with a limited distribution in the southern Sahara and northern Sahel: the berry-bearing Toothbrush Tree Salvadora persica, the small thorny shrub Sodad Capparis decidua and the small tree Maerua crassifolia. Other bird-rich woody species were without exception thorny (Balanites aegyptiaca, various species of acacia and ziziphus). In contrast, the five woody species most commonly distributed across the region (Cashew Anacardium occidentale, African Birch Anogeissus leiocarpus, Combretum glutinosum, Guiera senegalensis and Shea Tree Vitellaria paradoxa), representing 27% of the woody cover in the study sites, were rarely visited by foraging birds. In this sub-Saharan region, it is not total woody cover per se that matters to birds, but the presence of specific woody species. This finding has important implications: remote sensing studies showing global increase or decline of woody vegetation without identifying individual species have little value in explaining trends in arboreal bird populations. Local people have a large impact on the species composition of the woody vegetation in the Sahel, with positive and negative consequences for migrants wintering in this region. Faidherbia albida, the most important tree for birds in the sub-Saharan dry belt, is highly valued by local people and has the distinction of leafing in winter and being attractive to arthropods. On the other hand, migratory and African bird species have been negatively affected by the rapidly expanding cashew plantations since the early 1980s.","PeriodicalId":55463,"journal":{"name":"Ardea","volume":"111 1","pages":"143 - 174"},"PeriodicalIF":0.4,"publicationDate":"2023-07-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"47073654","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"生物学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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