Jan van der Kamp's scientific contributions

... Among raptors, the Marsh Harrier (Circus aeruginosus) is a good example of a species that is made up of populations with different degrees of migratory behaviour. In particular, breeding populations of northern, eastern and central Europe are migratory, mainly wintering in southern Europe and in the Sahel (sub-Saharan Africa), while breeding populations from the southern areas are resident (Cramp and Simmons 1994;Strandberg et al. 2008;Bavoux et al. 1994;Zwarts et al. 2009;Agostini and Panuccio 2010). The European Marsh Harrier population underwent a dramatic population decline from 1960 to 1980 due to drainage of wetlands, contamination and direct persecution, but has recovered in recent decades, when the species underwent a moderate increase, \10 %, and is currently classified as 'Secure' (Cramp and Simmons 1994;BirdLife International 2004). ...

... protection de la nature, ainsi que par l'article 3 de l'arrêté du 29 octobre 2009 fixant la liste des oiseaux protégés sur l'ensemble du territoire et les modalités de leur protection.[5,40- 42,46,47] En Wallonie, selon l'article 2 de la loi du 12 juillet 1973 de la conservation de la nature, les trois busards sont des espèces protégées et selon l'article 25 de cette même loi, ce sont des espèces de référence pour la définition de site Natura2000.[37][38][39]48] 1.2.7. ...

... Survival is one of the demographic determinants of population dynamics and understanding environmental causes of variation in survival may suggest processes that are leading to population declines. There is good evidence from single-species studies that weather affects the survival of many migrant species (Sillett et al. 2000, Mazerolle et al. 2005, Schaub et al. 2005, Altwegg & Anderson 2009, Zwarts et al. 2009a, Mihoub et al. 2010, LaManna et al. 2012. Weather may affect survival directly, for instance through increased metabolic requirements in cold weather (e.g. ...

... In the late 1960s and early 1970s, numerous Afro-Palearctic migrants -including the lesser kestrel -showed a sharp population decline (Sanderson et al. 2006, Iñigo andBarov 2010). During the 1990s, there have been several years of higher rainfall in the Sahel which has had a major impact on population recovery of Afro-Palearctic migrants e.g. common chiffchaff Phylloscopus collybita, Eurasian blackcap Sylvia atricapilla, common whitethroat Sylvia communis and common redstart Phoenicurus phoenicurus (Nevoux et al. 2008, Zwarts et al. 2023b, including probably the lesser kestrel. However, this positive trend has not been maintained in subsequent years, and like numerous steppe and grassland birds, the lesser kestrel is now declining in Spain (Bustamante et al. 2020). ...

... Several species (e.g. Willow and Wood Warbler, Spotted Flycatcher Muscicapa striata and European Pied Flycatcher Ficedula hypoleuca) are common in the Sahel during passage in the early dry season (October-November) but spend the rest of their wintering period farther south (Zwarts et al. 2023e). They may profit from the high food supply in savannah trees for some weeks during migration periods without having to cope with the harsh conditions there during the dry season in drought years. ...

... Both species are recorded historically as largely spending the winter in the Mediterranean and in sub-Saharan Africa (Cramp 1992, Urban et al. 1997, but during our surveys in the 2010s were recorded only rarely in Africa between 7 and 22°N except in Ethiopia where numbers were substantial (Figure 8 and 14 in Zwarts et al. 2023c). Small numbers were captured in The Gambia (King 2000, King & Hutchinson 2001 and the Djoudj, Senegal (Ottosson et al. 2001) in the 1990s, but both species are at present decidedly scarce across the Sahel except Ethiopia (Zwarts et al. 2023b), and are rare in winter in the hyper-humid zone in West Africa (Dowsett-Lemaire & Dowsett 2014, 2019, Languy 2019). Since the 1970s, an increasing number of Blackcaps remained during the winter in W Europe (Berthold et al. 1992), where they have become a common garden bird (Plummer et al. 2015). ...

... To conserve this species, it is essential to identify roost sites and their associated foraging areas, taking into account potential threats such as land use changes, or the use of pesticides for controlling outbreaks of potential prey species (Mullie 2021). Indeed, Sahel landscapes are anticipated to undergo substantial and rapid transformations in the coming decades due to development and climatic changes (Thiollay 2007, Zwarts et al. 2023c). Table 2. Results of separate generalised additive mixed models (GAMMs) fitted with Gaussian error distribution and identity link function used to examine the effect of sex and date, smoothed on daily metrics (response variables: mean daily distance and % of time flying) during resident days. ...

... The stored water is used during dry season for human and animal drinks. Zwarts, & van der Kamp, [24], confirmed that, the majority of resources in Chad, dry up as soon as the dry season reaches the months of January and February. The figure shows continuity of presence of water throughout the year. ...

... As the tropical rain belt moves south, insect abundance in the Sahel decreases as the area gradually dries up from November to May (Koleček et al. 2018). Many itinerant species seem to escape the peak of the Sahelian dry season by switching between staging sites, usually in a southward direction (Trierweiler et al. 2013, Zwarts et al. 2023a). However, some species like turtle-doves Streptopelia turtur, tawny pipits Anthus campestris, and marsh harriers Circus aeruginosus show non-breeding itinerant movements in different directions (Eraud et al. 2013, Briedis et al. 2016, Vansteelant et al. 2020). ...

... Another virtue, obviously, is that leave-less trees will not shade the crops during the growing season! And during the subsequent dry season, when other trees lose their foliage, the leaves of Faidherbia appear especially attractive for the caterpillars of the moths that are good food (both in their larval and mature stages) for insectivorous birds that then start to fuel up for northward migration (Zwarts et al. 2023a(Zwarts et al. , 2023b. ...