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Home range and foraging habitat selection by breeding lesser kestrels (Falco naumanni) in Greece
Journal of Natural History
Abstract and Figures
Home range size and foraging habitat use in breeding lesser kestrels (Falco naumanni), a bird species of conservation concern, were investigated during the breeding season of the species in 2008 in an intensively cultivated area of central Greece, using radio-tracking. Grasshopper (the main prey) densities were measured at the most important habitats (cotton, cereals, grasslands and margins). Home ranges were not significantly different between sexes either as overall means or during incubation and nestling periods. Movements of both sexes were non-random during incubation but random during the nestling period. Habitats used by males during incubation ranked as: margins > other > cotton > corn > cereals and during nestling period as: cereals > margins > grasslands > corn > cotton. Female habitat use greatly differed ranking as cereals > cotton > grasslands during incubation and as grassland > cotton > corn > cereals > margins during nestling period. Female habitat use seemed to be in disagreement with the conditions generally favouring prey availability, probably for reasons associated with low and uniform distribution of grasshopper densities over the habitats
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... Kestrel nest box colony was founded by us in 2001 in the village of Armenio (39 o 29'07''N, 22 o 41'39''E), in the Thessaly Plain and is listed in the Natura 2000 List as a Special Protected Area (SPA GR-1420011 "Periochi Thessalikou Kampou"). The nest boxes (n = 82) are placed in a pine stand(Vlachos et al., 2004(Vlachos et al., , 2015 Fig. 1). Over the last decade we have seen a dramatic increase in the Jackdaw population and encroachment of the Lesser Kestrel colony owing to a lack of natural nesting sites. ...
Anthropogenic changes in the natural environment have led to the need to find alternative resources to ensure the persistence of biodiversity. In birds, nest sites can be a limiting resource in stenotopic populations. A method of active protection is the building of nest boxes. However, attractive nest sites attract target species and their competitors. From the species conservation point of view, our target species was the Lesser Kestrel (Falco naumanni), whose populations have recovered owing to the establishment of nest box colonies across Europe. However, they have been outcompeted by Jackdaws (Corvus monedula) in recent years. Because corvids are
intelligent and aggressive, we had to artificially control the competition from Jackdaws to allow Lesser Kestrels to nest. We aimed to discourage Jackdaws from taking over the studied colony and to ensure the continued breeding of Lesser Kestrels by manipulating access to the nest boxes. Data were collected during three breeding seasons in a Lesser Kestrel nest box colony using two manipulations in which we prevented Jackdaw occupation by closing some of the nest boxes and then gradually opening them. We found a significantly lower probability of Lesser Kestrels nesting and lower breeding performance in the control year than in the years in which access to the boxes was manipulated. The field experiment shows the high efficiency of manipulating the accessibility of nest boxes by closing and opening them at the right time in the context of their occupation by the target species and thus influencing their breeding performance.
Share link: https://authors.elsevier.com/c/1i2Uh5liTFNy-4
... The other major threat to the Lesser Kestrel, the most important for some authors, is the loss of foraging habitat due to changes in land use and agricultural intensification. Several studies on habitat selection of Lesser Kestrels agree that the preferred habitats are grasslands and cereal crops during the nestling period , Vlachos et al. 2014, Christakis & Sfougaris 2021, Assandri et al. 2022. In our study area, 12.1% of herbaceous crops and 34.7% of pasture lands have been lost between 2003 and 2021 in favour of abandoned land, woody crops or non-productive areas (photovoltaic farms, intensive livestock farms, etc.). ...
Lesser kestrel (Falco naumanni, Fleischer, 1818) populations have been one of the best monitored bird populations in Spain over the last 70 years. These populations suffered a sharp decline between the 1950s and 1990s. Since then, periodic censuses showed a population increase that lasted until 2010s. In those years, numerous projects for the recovery of the species were also initiated (some EU LIFE Projects, among others), which have continued to the present day. However, despite conservation efforts, the Spanish Lesser Kestrel population, which include about 40% of the European breeding population, has declined at a rate of 6% per year since 2012. In this paper, we analysed changes in habitat and population size in 12 colonies located in La Mancha between 2003 and 2021 in order to identify possible causes of the current decline. This colonial species breeds in old buildings and roof area (a proxy of the house size) was the predictor that best accounted for the number of pairs in a colony in a given year. In addition, the extent of herbaceous crops (related with prey availability) explained a similar amount of colony size variance in 2021, while in 2003, the availability of large Orthoptera itself had a significant effect but a much lower effect size. The number of nest boxes affected positively the number of breeding pairs in 2021, but it explained only 1% of the variance. The decline of Lesser Kestrel population between 2003 and 2021 was largely explained by the decrease of the density of large orthopterans, their main prey. The model with minimum AICc value also included a positive association with changes in roof area and a negative association with rabbit density (possibly through a hyperpredation phenomenon). Other top models (i.e. ΔAICc ≤ 2 units) also showed negative effects of the loss of favourable land uses (pasture lands and herbaceous crops) on colony size, probably because it had caused a reduction in the availability of large Orthoptera. These changes in land use occurred less likely in areas protected by the Natura 2000 network and, therefore, it may have contributed to the conservation of the Lesser Kestrel population. However, other conservation measures such as the installation of nest boxes were not as efficient as expected.
... Hern andez-Pliego, Rodríguez and Bustamante (2017) reported that female lesser kestrels from southwestern Spain engaged in few long trips, while males performed frequent short trips. Moreover, Vlachos et al. (2015) found that incubating females breeding in a colony in Thessaly (Greece) foraged further than males. While our study was conducted at a very large colony, both these previous studies were conducted in small colonies. ...
Foraging specialization, whereby animals exploit only a minor fraction of the population's foraging home range or trophic niche, may arise as a response to increasing levels of intraspecific competition. This phenomenon may be particularly frequent in colonial species, when individuals breed in large aggregations and are constrained to exploit shared foraging areas surrounding the colony site where competition for access to food resources may be high. Foraging specialization may be driven by individual foraging site fidelity, occurring whenever individuals consistently target specific foraging sites, which may differ from those used by other colony members. We assessed the extent of foraging specialization in a colonial breeding raptor, the lesser kestrel, Falco naumanni, by estimating the repeatability of foraging movement patterns of 45 GPS-tracked individuals during both incubation and nestling rearing. We found that the consistency of individual movement patterns was generally higher during nestling rearing than during incubation. Nestling-rearing individuals, but not incubating ones, travelled along relatively consistent routes when targeting foraging grounds and tended to target the same foraging areas throughout the tracking period. In colonial birds, and likely in altricial species more generally, an increased individual foraging site fidelity during nestling rearing versus incubation may result from increased energy demands due to frequent nestling provisioning in addition to self-provisioning. By consistently exploiting previously visited foraging sites that are likely to be rewarding, nestling-rearing birds might indeed increase their foraging efficiency, shortening food-searching time and maximizing their foraging effort. In addition, the use of distinct foraging areas may reduce intraspecific competition for food, thus buffering an important cost of coloniality.
... Sexdependent habitat selection is quite widespread within vertebrates and may be related to sex differences in offspring provisioning (Bergan and Smith, 1989;Laforge et al., 2021;Ofstad et al., 2019;van Toor et al., 2011). On the one hand, in Greek intensive agricultural landscapes, Vlachos et al. (2015) reported that male lesser kestrels positively selected cereals and field margins while females preferred grasslands and cotton fields. On the other hand, Tella et al. (1998) andHernandez-Pliego et al. (2017) found no sex differences in habitat selection in Spain. ...
Gradients of agricultural intensification in agroecosystems may determine uneven resource availability for predators relying on these man-made habitats. In turn, these variations in resource availability may affect predators' habitat selection patterns, resulting in context-dependent habitat selection. We assessed the effects of gradients of landscape composition and configuration on habitat selection of a colonial farmland bird of prey, the lesser kestrel (Falco naumanni), relying on 76 GPS-tracked nestling-rearing individuals from 10 populations scattered along an agricultural intensification gradient. Analyses were conducted considering two ecological levels of aggregation (the population and the individual) and two spatial scales of habitat availability (the colony surroundings and the individual home-range). Overall, non-irrigated croplands and semi-natural grasslands were the most preferred habitats at both spatial scales. At the colony scale, lesser kestrels showed a preference for grassland compared to non-irrigated crops, whereas the opposite was the case within individual home-ranges. Conversely, croplands were positively selected with comparable intensity at both spatial scales. Strong selection for grassland at the colony scale highlights the importance of this semi-natural habitat for the species. The weaker preference for grassland at the home-range scale is likely due to the phenology and structure of the vegetation in the late breeding season. Spatial scale differences in selection patterns may thus derive from spatio-temporal changes in resource availability through the breeding season. The strength of selection for the two most used habitats varied markedly among individuals. At the spatial scale of the colony, individual selection strength for grasslands increased with decreasing compositional diversity of the surrounding landscape, suggesting that agroecosystem heterogeneity may at least partly buffer the loss of semi-natural habitats. At the within home-range scale, higher cropland availability reduced the strength of individual preference for this habitat, suggesting a negative functional response possibly related to density-dependent processes acting on foraging movements. Our study provides evidence that farmland species show context-dependent habitat selection patterns in response to landscape gradients shaped by agricultural intensification as well as by intrinsic characteristics and habitat availability. Our findings highlight the importance of addressing both individual and population-level variability and considering multiple spatial scales in studies of habitat selection to inform species' management and conservation.
... Per una popolazione della Grecia centrale localizzata in un'area intensamente coltivata è stata osservata una differente preferenza di ambiente trofi co tra sessi e tra stadi riproduttivi negli esemplari di 5 differenti coppie (Vlachos et al., 2014): i movimenti di entrambi i sessi Figura 7. Segregazione spaziale delle aree di foraggiamento di colonie di grillaio vicine tra loro (Gravina in Puglia, Matera, Altamura). Ciascun poligono rappresenta l'home range (MCP 95%) di un individuo tracciato con dispositivo GPS durante il periodo riproduttivo. ...
The Lesser Kestrel experienced steep population declines in the second half of the 20th century. The main cause for this decline in breeding grounds has been habitat degradation, provoked by agricultural intensifi cation and associated land use changes.
The replacement of grazed grasslands, extensive dry cereal and pulses with taller and denser crops (e.g. sunfl ower, maize, vineyards and other perennial crops) has lead to two important effects: the reduction of large insects abundance and the decrease of access to prey. The use of pesticides reduced further prey populations. Some formerly declining populations (e.g. in France and in the Iberian Peninsula) have now increased following the
implementation of conservation measures. Its breeding population seems to be stable and even growing now, especially in SW Europe, with an approximate estimate for the European breeding range of 30,500-38,000 pairs. Spain holds the most important
breeding population in Europe, followed by Italy and Greece. In Italy, the breeding population in the 90’s was of 1,300-1,500 pairs, but recently the species has shown a numerical increase and an extension of the breeding area.
The Action Plan has updated the knowledge about distribution and size of
Italian populations of Lesser Kestrel, now estimated in 6,600-9,200 pairs
and nesting in Lombardy, Emilia-Romagna, Lazio, Molise, Basilicata, Apulia, Calabria, Sardinia and Sicily.
The Plan examines threats and limiting factors in Italy of which at least 12
were found to have a high impact on reproductive success and population
density of the Lesser Kestrel leading to a lack of trophic availability (use of
pesticides and other food chain pollutants, loss of trophic habitat and of
trophic habitat structural complexity), higher energy costs for foraging activity
(development of infrastructure and expansion of built-up areas, enlargement
of irrigation systems, afforestation of marginal areas, overgrazing), poor
accessibility to prey (replacement of steppe areas and traditional cereal
crops with different higher, dense and/or permanent cultivations), loss of
nests sites (collapses of farm buildings, renovations of farm and historic
urban buildings, procedures of ban on the access to historic urban buildings
for hygienic reasons, abandonment of the maintenance of artifi cial nests
installed due to a lack of funds).
Loss of sites of pre-migratory roost produces a high decrease of fi tness in
critical periods and then increase of individual mortality in long-term period,
while actual lack of knowledge and consequent impossibility to preserve
migration routes, stop-over sites (roosts) and wintering areas can hinder
conservation measures.
Fitness decrease of the principal nesting and wintering areas, caused
by the climate change in place, determines a high increase of youth
mortality pre- and post-fl edging.
As well as threats and limiting factors above mentioned, the plan
identifies and describes additional threats that appear likely to have a
medium and low impact.
Finally, various actions have been identifi ed in order to achieve the
purpose of the plan, which is to improve the status of the Lesser Kestrel
and in particular:
• to have a stable and possibly growing Italian population of Lesser Kestrel
over the next 10 years and more specifi cally: a) to maintain the largest
populations and those that are currently in a safe state of conservation
(Basilicata, Apulia and Sicily); b) to consolidate the rise of the smallest
populations (Sardinia), c) to increase the population of recent settlements
(Lombardy, Emilia- Romagna, Lazio, Molise and Calabria);
• to increase the breeding area by favouring the recolonization of previously
abandoned areas, the colonization of new potentially suitable areas through
the improvement of their habitats and the overcoming of any existing and
hindering obstacles for the establishment of Lesser Kestrel (scarcity of
reproductive sites, excessive anthropic disturbance, etc.).
... Natural cavity-nesting animals that roost or breed use holes in buildings or humanmade constructions like nest boxes [1]. Nest boxes can either supplement existing natural cavities or replace them when destroyed and can be a technique in the toolbox of conservation in order to recover declining populations (e.g., Lesser Kestrel, Falco naumanni; [2]). Some countries, such as Germany [3] and Poland [4], have legislated rules that require homeowners to install nest boxes as compensation for destroyed nest sites. ...
As is well known, endemic island bird species are especially vulnerable to extinction from anthropogenic environmental change and reduced fitness compared with mainland taxa. The Cyprus Scops Owl Otus cyprius is a recently recognized island endemic species whose ecology and breeding biology have not been extensively studied. It nests mainly in holes in trees and buildings so the felling of old trees, modern architectural practices, and the renovation of old houses in villages may reduce nest site availability; its population trend is also unknown. Therefore, to better determine its ecological requirements and habitat preferences we placed nest boxes in villages adjacent to the forest, in the forest, and in the ecotone between them, and used breeding success as our indicator of habitat suitability. We found that breeding parameters like laying date, clutch size, length of the incubation period, hatching day, hatching success, and number of nestlings did not differ between the three habitats. Despite the low level of nest box occupancy rate (5 to 11 %) the endemic Cyprus Scops Owl readily breed in artificial nests. Therefore, although we are unaware of any current threats to the Cyprus Scops Owl, we recommend that its conservation be prioritized, including studies, monitoring, habitat conservation, and the provision of nest boxes.
... These studies showed a clear preference for non-irrigated arable lands as well as for scrubs and herbaceous crops in eastern Spain (Vidal-Mateo et al. 2019) and a preference for dry cereals and grasslands in central Greece, but with significant differences between sexes and stages of the breeding season (i.e. incubation versus nestlingrearing, Vlachos et al. 2015). Lesser kestrels mainly forage on large insects (Di Maggio et al. 2018), opportunistically targeting orthopterans flushed during cereal crop harvesting (Catry et al. 2014). ...
Farmland habitats host important populations of several threatened bird species. So far, how to reconcile farmland management with the maintenance of viable populations of these taxa is a major challenge for conservation biology. Southeastern Italy hosts ca 7000 pairs of breeding lesser kestrels Falco naumanni, representing one of the European strongholds of this small colonial raptor of conservation concern. We firstly assessed the relative importance of managed crops versus semi-natural grasslands in determining the local abundance of lesser kestrels at the landscape scale, and we successively studied the foraging habitat preferences at a smaller spatial scale. Surveys of foraging birds were associated with land-use collection at 191 homogeneous habitat sampling parcels from 14 plots of 16 km2 each, uniformly distributed over a 2400 km2 area. Each plot was visited six times during the 2017 breeding season (May–July). Land-use markedly changed along the season, unripe cereals being dominant in May, while harvested cereal crops prevailed in July. Land-use did not affect lesser kestrel distribution early in the season while foraging birds were more abundant in plots with a greater proportion of harvested cereal crops and a lower one of semi-natural grassland in the late breeding season. In accordance, the analysis of foraging habitat preferences within plots showed that in May unripe cereal crops and semi-natural grasslands were used proportionally to their availability. In June and July, harvested cereal crops were used more than expected from their availability, while semi-natural grasslands were significantly avoided. Our landscape-scale analysis thus indicates that semi-natural grasslands are much less used in comparison to harvested crops during the mid and late parts of the breeding season, suggesting that lesser kestrel may be able to take advantage of crop management practices more than other farmland birds of conservation priority.
Ixodes lividus (Koch, 1844) is a specific ectoparasite of sand martin (Riparia riparia). Despite the distribution range of I. lividus covering the majority parts of the Eurasian continent, there have been no reports for infestation of this tick from lesser kestrel (Falco naumanni). We collected a total of 306 ticks (n = 94 from adults, n = 212 from nestlings) from 20 adults and eight nestlings in colonies of Ikh Nart Nature Reserve in southeastern Mongolia. Ticks were identified as Ixodes lividus according to their morphological characteristics and molecular approach (mtDNA; 610-bp-long COI gene). This report represents the new avian host for I. lividus from the Mongolian semi-desert region. We detected ticks from 10 adults (four males and six females; 10/20 birds examined), resulting in overall prevalence of 50.0% for adults. The mean number of ticks
per adult host was 4.9 (ranged between one and 38), and there were no differences in the number of ticks in females and males (t = 0.09, df = 8.0, p = 0.9). All nestlings were infested by I. lividus (prevalence = 100%). Moreover, infestation level (mean number of ticks) did not differ by nestling age groups (F4,24 = 1.13, p = 0.36); however, prevalence of nestling infestation decreased as nestlings aged (age groups; 1–5 days = 100%; 6–10 days = 87.5%; 11–15 days = 62.5%; 16–20 days = 75%; 20 + days = 37.5%). Since parasitic infectious diseases are known as determinants of population dynamics, species of interest should be examined for ectoparasites for further conservation.
Σύνοψη
Προτείνεται η δημιουργία Οικολογικού Διαδρόμου κατά την έννοια του ν. 4685/2020 ως ζώνης διασύνδεσης μεταξύ των ΖΕΠ GR1220010, GR1230004, GR1230005 και GR1230006, προκειμένου να διατηρηθεί η ελευθεροεπικοινωνία του Κιρκινεζιού και των άλλων προστατευόμενων ειδών ορνιθοπανίδας, που είναι είδη χαρακτηρισμού των ΖΕΠ αυτών και χρησιμοποιούν τα ψευδοστεπικά ενδιαιτήματα της κοιλάδας Αξιού και πεδιάδας Κιλκίς για τροφοληψία ή/και αναπαραγωγή. Στον προτεινόμενο ΟΔ θα πρέπει να οριστούν ρυθμίσεις κατάτμησης των φωτοβολταϊκών πάρκων, ελάχιστων αποστάσεων και ποσόστωση συνολικής κατάληψης Φ/Β, αναφορικά με τη συνολική έκταση αρόσιμης γης.
Η αναγκαιότητα του ΟΔ προκύπτει από:
1. Το Κιρκινέζι ως είδος χαρακτηρισμού των 4 ΖΕΠ διατηρεί συνολικά 24 αποικίες με εκτιμώμενο πληθυσμό 180 - 220 ζευγάρια.
2. Μόνο μία αποικία με 12 ζευγάρια βρίσκεται εντός ορίων της ΖΕΠ GR1230006 “Περιοχή Ανθόφυτου”
3. Λόγω του ότι οι αποικίες βρίσκονται εντός οικισμών και αστικού ιστού, όπου είναι περιορισμένες οι δυνατότητες λήψης μέτρων, θα πρέπει να δοθεί έμφαση στη διαχείριση και προστασία του ενδιαιτήματος τροφοληψίας που τις περιβάλλει
4. Οι περιοχές τροφοληψίας του είδους βρίσκονται κατά >80% εκτός Ν2Κ και προκειμένου να αντιμετωπιστεί η κύρια απειλή που είναι η αλλαγή χρήσης γης απαιτούνται ρυθμίσεις για τη διατήρηση ενός ικανοποιητικού ποσοστού του ενδιαιτήματος του, που βρίσκεται εκτός ΖΕΠ
5. Οι στόχοι διατήρησης για το είδος (ΦΕΚ Β' 3118 / 10.05.2023) δεν καλύπτονται από το υφιστάμενο δίκτυο Ν2Κ
6. το γεγονός ότι στην περιοχή Ανθόφυτου, Ν. Σιρράκιου και Βακούφιου, η περιοχή τροφοληψίας καταλαμβάνεται από Φ/Β κατά 11,58%, 13,47% και 12,75% αντίστοιχα ενώ στη ΖΕΠ Έλους Αρτζάν τα σχεδιαζόμενα Φ/Β καταλαμβάνουν 8,54% της έκτασης της ΖΕΠ, ενώ ποσοστά >5% περιοχής τροφοληψίας καταλαμβάνονται από Φ/Β και στις περιοχές Ακροποτάμου, Λιμνότοπου, και Βαλτουδίου
Οι βασικές ρυθμίσεις που θα πρέπει να ισχύσουν στον ΟΔ αναφορικά με το Φ/Β είναι οι παρακάτω:
1. αδειοδότηση παραγωγής Φ/Β μόνο εφόσον γίνει πλήρης απογραφή των αποικιών του είδους και των περιοχών τροφοληψίας στην Π.Ε. Κιλκίς
2. σε ακτίνα έως 2 χλμ. γύρω από τις αποικίες, το ποσοστό κάλυψης Φ/Β δεν μπορεί να υπερβαίνει το 0,5% της ζώνης τροφοληψίας, δηλαδή 320 στρέμματα αθροιστικά
3. σε ακτίνα 2-4,5 χλμ. από κάθε αποικία, τα Φ/Β να καλύπτουν έκταση μικρότερη του 1% της ζώνης τροφοληψίας κάθε αποικίας, δηλαδή έκταση <630 στρεμμάτων και όχι σε ενιαία εγκατάσταση ή συνεχόμενη έκταση
4. σε ακτίνα >4,5 χλμ κι εντός ΟΔ τα Φ/Β να μην υπερβαίνουν το 3% της ζώνης τροφοληψίας, δηλαδή 1.900 στρέμματα και όχι σε ενιαία εγκατάσταση ή συνεχόμενη έκταση
Η μείωση των δυσμενών επιπτώσεων φ/β πάρκων στα ενδιαιτήματα τροφοληψίας του Κιρκινεζιού μπορεί να επιτευχθεί εφόσον η αδειοδότηση γίνεται με συγκεκριμένες προϋποθέσεις. Για τον λόγο αυτό καταθέτουμε πρόταση δημιουργίας Οικολογικού Διαδρόμου, προκειμένου να τεθούν όροι και περιορισμοί για την αλλαγή χρήσης γης που επιφέρουν τα Φ/Β στο ενδιαίτημα τροφοληψίας του Κιρκινεζιού.
The sex ratio of nestlings is a crucial population determinant in rare and/or endangered species. We investigated
the role of female body condition and female-related traits in Lesser Kestrel (Falco naumanni) nestling sex allocation at a
nest-box colony in central Greece. We used the total clutch volume and size, female weight, hatching dates, body length,
wing length, tail length, tarsometatarsus, and bill length as explanatory variables of the number of male nestlings (the
response variable) using CART model analysis. This analysis showed that the reproduction output was biased towards male
nestlings when female parents were shorter in body length and clutch size and volume were smaller. The skewed sex ratio
favoring females, 1:2.35, suggests that when female parents are in good condition, they invest most in good-quality female
nestlings, providing a reproductive advantage and increased long-term fitness.
The Northern Goshawk Accipiter gentilis typically prefers woodland habitat for nesting and hunting. In recent decades, however, the species has started colonising urban environments across Europe. Here I present the first study on the ranging behaviour of urban-breeding Goshawks. Each year from 1997 to 1999, I tracked a different adult male during the breeding season in the city of Hamburg, Germany (858 hours of total tracking time; n = 5364 radio-fixes). All corresponding pairs raised young in the year of data collection (3, 3 and 4 juveniles). Average home range size was 863 ha (100% Minimum Convex Polygons). Males spent 88% of daylight hours in patches of urban green space (mainly parks) and made short but regular hunting excursions into the matrix of built-up habitat. Built-up habitat was used less frequently than expected from its percentage availability. However, 42% of all recorded kills (n = 143) were made in this habitat type, indicating that it offered good foraging opportunities. Hawks spent 9.7% of daylight hours in active flight (1.8% inter-perch flights, 7.9% soaring). Daily activity patterns were bimodal, with peaks in the early morning and in the evening. I observed one hawk hunting regularly after sunset under artificial light conditions. Goshawks hunted by perched hunting (49%), soaring (33%), and fast contour-hugging flights (11%; n = 220 hunts). Average hunting success was 16% (n = 176 directly observed attacks), or one kill every 35 min of active flight. Home range size was smaller, time spent flying was shorter, and hunting success was higher for the monitored urban hawks than for non-urban individuals from earlier studies. Taken together, my data suggest that living conditions for Goshawks are more favourable in the city of Hamburg than in many non-urban environments.
Measures of niche breadth and overlap that depend on the distribution of individual among resource states (ecological categories) should be independent of the relative abundance of the species and of the number of resource states considered. Such measures should also take into account the degree of distinctness of the resource states from the point of view of the organisms concerned. An ecoassay of the distinctness of resource states may well be easier and more meaningful than measurements of physical and chemical factors. We propose that the species composition of communities utilizing different resource states may be used to develop weighting factors with which each state may be weighted in proportion to its degree of distinctness. The weighting factors are used in the development of indices of niche breadth and overlap that correct for variation in the range and distinctness of resource states and that suffer less from human subjectivity than do the measures used to date. The use of such indices and the relationship of niche overlap to competition are discussed.
Reversed sexual dimorphism in size (RSD) occurs in most species of several taxonomic groups of birds. The hypotheses proposed to explain this phenomenon are examined theoretically, using inequalities to state selection in the most rigorous possible terms. The most pertinent empirical evidence is also examined critically. Proponents of hypotheses on the evolution of RSD have failed to consider the genetic constraints on the evolution of dimorphism. Selection for dimorphism can act on only that small portion of the genetic determination of body size that is sex limited. In general, selection for body size is much more likely to lead to a similar change (e.g. larger) in both sexes than to dimorphism. The most popular hypotheses involve selection for size-related differences in foraging ability. It is unlikely that there is variation in size-related foraging differences available for selection in a monomorphic, ancestral population. Foraging differences between the sexes cannot lead to the evolution of RSD; evolution of large and small morphs of both sexes is a more likely outcome. Selection for sex-role differentiation factors (e.g. large females lay larger eggs, small males are more agile in flight) can lead to the evolution of RSD, but only if the magnitudes of opposing selection for small males and for large females are equal. Combining selection for size-related foraging differences with selection for sex-role differentiation factors hinders the evolution of RSD until the sexes differ in size by 3 S.D. Empirical evidence supports this assertion: statistically significant differences between the sexes in the size of prey taken are found only in highly dimorphic species. The sex-role differentiation factors that have been proposed appear unlikely to provide the equal selection necessary for the evolution of RSD. Several authors have proposed that small size in males is selected for foraging ability and large size in females for some sex-role differentiation factor. Males cannot be more efficient foragers without females being less efficient and efficiency cannot be a factor only when the male is feeding his family. RSD cannot evolve in monogamous species if large females survive less well than small males.
We examined the effects of backpack radio transmitters on Prairie Falcon (Falco mexicanus) reproduction (percentage of occupied territories producing young and number of nestlings produced) over four years. In addition, we observed falcon aeries during brood-rearing to determine attendance at the nest and in the territory, prey delivery rates, and prey composition. We found no effect of radio tagging on Prairie Falcon productivity (nesting success and brood size) among years, although productivity varied significantly among years. The sex of the falcon tagged did not affect productivity. Radio-tagged members of pairs did not differ significantly from un-tagged members of pairs in territory attendance, nest attendance, prey delivery rates, or caching rates. Nestlings raised by radio-tagged parents attained masses similar to those reared by control parents. During low prey years, radio-tagged males brought a greater proportion of small birds and reptiles, and fewer mammals to the nest area than control males.
Gives details of habitat selection and interspecific habitat relations by ferruginous Buteo regalis, red-tailed B. jamaicensis and Swainson's hawk B. swainsoni in the Columbia River basin and the Great Basin, paying particular attention to: the significance of perches and topography; ground cover and prey distribution; and diet and prey preference. Discriminant analysis indicates foraging behaviour (particularly the dichotomy between perch and aerial foraging) as the key variable, with open space next in significance. Morphological correlates of foraging behaviour are indicated. Red-tailed hawk primarily hunts by surveying the ground from an elevated perch. Swainson's hawk glides slowly, and may occupy habitats without perches except for the nest tree. Ferruginous hawk glides more rapidly. A simple model of prey detection and capture is presented. Influences of competition and predation are shown. Other factors in raptor habitat selection are outlined - prey habitats, nest-site selection and roosting requirements. -P.J.Jarvis