Ronny Steen

A Portable Digital Video Surveillance System to Monitor Prey Deliveries at Raptor Nests

Resumen Los sistemas de vigilancia por video desarrollados recientemente permiten registrar variables como la deteccion del movimiento. En este estudio, describo el uso de un sistema de vigilancia con video portatil para analizar las entregas de presas en cajas nido usadas por Falco tinnunculus. El sistema consistio en un mini DVR con deteccion de movimiento por video, que detectaba movimiento y activaba las grabaciones inmediatamente. Las grabaciones se guardaron en una tarjeta digital de seguridad (Tarjeta-SD). La duracion de la grabacion activada de video fue ajustable, de 5 a 30 seg. Cuando se selecciono la resolucion mas alta, una tarjeta-SD (2 GB) almaceno aproximadamente 150 minutos de grabacion de video (aproximadamente 1800 secuencias con intervalos de 5 seg.). Con una bateria 12 volt DC (80 Ah) como fuente de suministro de electricidad, cada unidad podria durar aproximadamente 14 dias. El costo total por unidad fue aproximadamente de US

Prey Delivery Rates as Estimates of Prey Consumption by Eurasian Kestrel Falco tinnunculus Nestlings

700. Este estudio se realizo a lo largo de 164 dias, se em...

Size-biased allocation of prey from male to offspring via female: family conflicts, prey selection, and evolution of sexual size dimorphism in raptors.

Steen R., Løw L.M., Sonerud G.A., Selås V. & Slagsvold T. 2011. Prey delivery rates as estimates of prey consumption by Eurasian Kestrel Falco tinnunculus nestlings. Ardea 99: 1–8. In altricial birds the type of prey selected by parents for their nestlings may affect the allocation of time and energy spent on hunting, preparing prey and feeding the nestlings, which in turn may affect the rate of provisioning. Raptors take relatively large prey items, which facilitates the quantification of rates of prey items and prey mass delivered to nestlings. Estimates of rates of prey delivery in raptors are nevertheless few and have been based on direct observations from a hide in combination with analyses of prey remnants and regurgitated pellets. To obtain better estimates we video monitored prey deliveries at 55 nests of Eurasian Kestrels Falco tinnunculus. Of the 2282 prey items recorded, voles were most abundant by number, followed by birds, shrews and lizards, while insects and frogs were rare. An average brood of 4.3 nestlings was estimated to consume 18.3 g/h, hence a nestling consumed on average 4.2 g/h. This is equivalent to 67.8 g/d, given an average daily activity period of 16.1 h. The estimated delivery rate of prey items required to feed an average brood in our study was 91 per h if the kestrels had provided only insects, and 3.4, 1.9, 0.83 and 0.52 if they had provided only lizards, shrews, voles or birds, - respectively. This corresponds to one prey delivery per 40 s if feeding solely on insects and one per 18, 32, 75 and 120 min if feeding solely on lizards, shrews, voles or birds, respectively. We argue that kestrels in the boreal forest would be unable to raise an average brood solely on insects or lizards, unlikely to do so solely on shrews, but able to do so solely on voles in a vole peak year.

The feeding constraint hypothesis: prey preparation as a function of nestling age and prey mass in the Eurasian kestrel

In birds with bi-parental care, the provisioning link between prey capture and delivery to dependent offspring is regarded as often symmetric between the mates. However, in raptors, the larger female usually broods and feeds the nestlings, while the smaller male provides food for the family, assisted by the female in the latter part of the nestling period, if at all. Prey items are relatively large and often impossible for nestlings to handle without extended maternal assistance. We video-recorded prey delivery and handling in nests of a raptor with a wide diet, the Eurasian kestrel Falco tinnunculus, and simultaneously observed prey transfer from male to female outside the nest. The male selectively allocated larger items, in particular birds and larger mammals, to the female for further processing and feeding of nestlings, and smaller items, in particular lizards and smaller mammals, directly to the nestlings for unassisted feeding. Hence, from the video, the female appeared to have captured larger prey than the male, while in reality no difference existed. The female’s size-biased interception of the male’s prey provisioning line would maximize the male’s foraging time, and maximize the female’s control of the allocation of food between her own need and that of the offspring. The male would maximize his control of food allocation by capturing smaller prey. This conflict would select for larger dominant females and smaller energy-efficient males, and induce stronger selection the longer the female depends on the male for self-feeding, as a proportion of the offspring dependence period.

Delivery of Common Lizards (Zootoca (Lacerta) vivipara) to nests of Eurasian Kestrels (Falco tinnunculus) determined by solar height and ambient temperature

The feeding constraint hypothesis states that an inability of young nestlings to ingest prey included in the diet of older nestlings and adult birds affects the evolution of parental behaviour, and predicts that the extent of prey preparation would increase with prey size and decrease with nestling age. In the Eurasian kestrel, Falco tinnunculus, a small raptor with a wide diet, parents often prepare prey prior to delivery at the nest, most notably by decapitation. We studied this behaviour by video monitoring prey deliveries at 29 nests for a total of about 200 days over 3 years. The probability of a prey item being decapitated prior to delivery differed between prey types and prey sizes; none of the insects or common lizards, Zootoca vivipara, and almost none of the shrews (Soricidae) were decapitated, whereas voles (Microtinae) and birds were commonly decapitated. For voles the probability of being decapitated decreased with nestling age, which supports the feeding constraint hypothesis because the nestlings’ gape size limit and swallowing capacity would increase with age. For both voles and birds the probability of being decapitated increased with prey body mass, suggesting that kestrel nestlings may be unable to swallow, digest or egest skulls from larger prey. We suggest that the extent to which kestrel parents decapitate prey prior to delivery is an effect of their nestlings’ age-dependent swallowing capacity and that the age of the nestlings therefore imposes constraints on the kestrel parents’ foraging behaviour.

A Bank Vole (Myodes glareolus) with Complete Leucism Captured by a Eurasian Kestrel (Falco tinnunculus) in Norway

Recent development in video monitoring has allowed collecting of data on prey deliveries at raptor nests, and this offers an opportunity to relate prey selection to short-term changes in environmental factors on a scale of hours. Whereas raptors may specialize on ectothermic prey at southern latitudes, only some generalist raptors may include such prey in their diet at northern latitudes. In particular, at northern latitudes the activity pattern of ectothermic reptiles is strongly dependent on the prevailing weather conditions. To test whether this dependence affects the exposure of reptiles to raptors, we used video recording of prey deliveries at nests of the Eurasian Kestrel (Falco tinnunculus L., 1758) at 61°N in Norway, where the Common Lizard (Zootoca (Lacerta) vivipara (Jacquin, 1787)) is the only lizard available to kestrels. The probability that a prey item delivered at a kestrel nest was a lizard increased towards midday and also increased independently with increasing ambient temperature, which...

Direct and indirect weather impacts on spring populations of lesser spotted woodpecker (Dendrocopos minor) in Norway

Small mammals with leucism are very rarely recorded, most likely because the probability of surviving to maturity would be very low for abnormal, white individuals. Here we report a record of a bank vole (Myodes glareolus) with complete leucism delivered to a nest of the Eurasian kestrel (Falco tinnunculus) in the boreal forest in SE Norway.

Evolution of parental roles in raptors: prey type determines role asymmetry in the Eurasian kestrel

Abstract In Norway, a positive relationship between spring numbers of lesser spotted woodpecker (Dendrocopos minor) and previous June temperatures has been interpreted as an effect of temperatures on woodpecker survival and reproduction during the breeding season. This article considers the possibility that woodpecker numbers are related to the abundance of the moth Argyresthia goedartella in the current year. Larvae and pupae of A. goedartella are important food for lesser spotted woodpeckers in early spring when few other surface-living invertebrates are available. The occurrence of this moth depends on the flowering of birch (Betula spp.) and alder (Alnus glutinosa), which in turn is influenced by June temperatures in the preceding year. Spring numbers of the lesser spotted woodpecker in two regions of Norway were compared with a trapping index of A. goedartella and weather variables assumed to influence the woodpeckers’ breeding success and adult survival. The best multiple regression model included December temperatures and moth indices, supporting the hypothesis of a strong impact of A. goedartella on spring survival. Conservation strategies for the lesser spotted woodpecker should therefore focus not only on minimum areas of deciduous forests with decaying wood, but also on the availability of the moths’ host trees, birch and alder.

Succession of beetles (genus Cis) and oribatid mites (genus Carabodes) in dead sporocarps of the red-banded polypore fungus Fomitopsis pinicola

Raptors deviate from the norm among provisioning birds by having asymmetric parental roles, with the female brooding and feeding offspring, and the male providing food, assisted by the female from the latter part of the rearing period. To investigate the poorly understood evolution of role asymmetry in raptors at an intraspecific level, we videorecorded prey delivery and handling in 25 nests of the Eurasian kestrel, Falco tinnunculus, with prey types ranging in size from insects via lizards and mammals to birds, and simultaneously observed prey transfer from male to female outside the nest. As the nestlings aged, the male was more likely to allocate prey items directly to them for unassisted feeding, rather than to the female for further processing and feeding of the nestlings. This switch occurred earlier for lizards than mammals and birds, and earlier for smaller than larger mammals. The time needed to ingest a prey item decreased from birds via mammals to lizards, and was particularly short for insects. The switch from nestlings being fed dismembered prey to nestlings ingesting prey unassisted occurred earlier for lizards than mammals and birds, and earlier for smaller than larger mammals, while all insects were ingested unassisted. Thus, the female could be relieved from dismembering prey, and start hunting, earlier if all prey were lizards rather than mammals and birds, if all mammalian prey were smaller, and in particular if all prey were insects. Because providing for the family selects for small body size, extended confinement of the female as a sedentary food processor for offspring would leave greater potential for differential selection on male and female body size. This potential would vary geographically with the composition of the kestrels diet, and be larger where the diet contains fewer insects and lizards and more mammals and birds.

Nonparental Infanticide in Colonial Eleonora’s Falcons (Falco eleonorae)

Abstract Dead sporocarps contribute to forest biodiversity by supporting a specialised decomposer fauna. However, detailed succession studies are few and microarthropods are rarely included. In a spruce-dominated forest reserve near Oslo in southern Norway, sporocarps of Fomitopsis pinicola with known age since death (0–5 years) were sampled and invertebrates extracted by Tullgren funnel. While living sporocarps of this species were rarely attacked by tunnelling invertebrates, dead sporocarps were rapidly colonised by a diverse fauna. The youngest pore layers were consumed first, and after five years, the remaining parts were strongly fragmented. Among 16 beetle species, Cis glabratus and Cis quadridens dominated. Another abundant group in dead sporocarps was oribatid mites belonging to the genus Carabodes, with a total of 10 species. Seven of these colonised during less than one year. While there were few significant changes in the density of adult Cis specimens during decomposition, and C. glabratus dominated all years, the Carabodes community underwent considerable changes. Carabodes femoralis dominated during the three first years, after which Carabodes areolatus and Carabodes reticulatus took over the dominance. These three Carabodes species are rare in Norwegian coniferous forest soil. Dead sporocarps of various polypore fungi may represent important microhabitats for sustaining the diversity of Carabodes mites in Fennoscandian coniferous forests.