3 research outputs found
Investigating the effects of environmental variables on martial eagle breeding performance in the Kruger National Park - MSC Data.
Within South Africa martial eagles reporting rates have decreased by almost
60% over the last 2 decades. Similar declines have also been reported within
Kruger National Park (KNP), which is regarded as a stronghold for this species.
Declines within KNP have been attributed to the low productivity rates. As apex
predators, marital eagles are considered to be good indicators of ecosystem
health, being sensitive to the cumulative effects of disturbance down the food
chain. Changes in the breeding performance of martial eagles may therefore
indicate broader environmental change within the ecosystem. In this study, we
aim to explore which environmental variables (e.g. climate, land cover, tree
cover, fire and elephant abundance) within each territory correlated with martial
eagle breeding performance in the hope that we may better understand which variables
affect martial eagles breeding performance and whether these may have changed
over time to cause the low levels of fecundity presently seen within KNP. We found
that breeding productivity (young per territorial pair) was positively
influenced by higher precipitation and Normalized Difference Vegetation Index (NDVI)
and negatively impacted by high temperatures during the previous year. Breeding
rate (breeding attempt per territorial pair) appeared to be negatively
influenced by higher tree cover within 6km of the nest site. Nesting success
(outcome of a breeding attempt) was correlated with higher NDVI and lower
relative levels of precipitation during the previous year. Using longer term
climatic data and the relationship between climate in the previous year and
productivity, (the variable which directly relates to annual fecundity), we hindcast
the predicted productivity over the last 3 decades (2018-1986) to explore
whether change in climate conditions (precipitation, temperature and NDVI)
might reveal declines in productivity. No such declines were predicted, thus,
our results do not explain why productivity has declined within KNP.</p
Nest boxes buffer the effects of climate on breeding performance in an African urban raptor (dataset)
As the world’s
human population increases, transformation of natural landscapes into urban
habitats continues to increase. In Africa, rates of human population growth and
urbanisation are among the highest in the world, but the impacts of these
processes on the continent’s biodiversity remain largely unexplored. Furthermore,
the effects of ongoing anthropogenic climate change are likely to be severe and
to interact with urbanisation.
Some organisms appear resilient to
urbanisation, and even proliferate in human-modified environments. One such
species is the peregrine falcon Falco peregrinus in Cape Town, South
Africa. Using a long-term data set (1989-2014), we investigate the relationship
between breeding attempts, timing of breeding and breeding performance under
varying weather conditions. Exploring these issues along an urbanisation
gradient, we focus on the role of artificially provided nest boxes, and their
capacity to buffer against extreme weather events.
Pairs in more urbanised areas, and particularly those in nest boxes,
were more likely to breed and to commence breeding earlier. Additionally, pairs
using nest boxes were more likely to breed in years with higher rainfall. Warm
and dry weather conditions generally advanced the timing of breeding, although this
relationship with weather was not seen for urban pairs using nest boxes.
Furthermore, weather did not impact breeding performance directly (breeding
success and fledged brood size), but timing of breeding did, with earlier
breeders producing more fledglings.
Our
study shows that falcons breeding in specially provided nest boxes were less
sensitive to local weather dynamics than pairs using more natural nest sites.
This has important implications as it suggests that the managed provision of
such nesting sites can help this key urban species to cope with extreme weather
events, which are predicted to increase with climate change
Contrasting parental color-morphs increase regularity of prey deliveries in an African raptor: Data
The paper based on this dataset has been published in Behavioral Ecology with the title "Contrasting parental color-morphs increase regularity of prey deliveries in an African raptor"Abstract: Disassortative mating in color-polymorphic raptors is a proposed mechanism for the maintenance of color polymorphism in populations. Selection for such a mating system may occur if there are fitness advantages of mating with a contrasting morph. In the black sparrowhawk (Accipiter melanoleucus), mixed-morph pairs may have a selective advantage, since they produce offspring which have higher survival rates. Two hypotheses, which may explain the mechanism, are the 'avoidance-image' and 'complementarity' hypotheses: The first suggests that within a predator's territory, prey develop a search-image for the more commonly encountered parental morph, for example, the male morph during incubation and brooding. Females of a contrasting morph to their partner would then have higher capture rates once they commence hunting in the later nestling phase. Thus, the avoidance-image hypothesis predicts higher provisioning rates for mixed-morph pairs. Alternatively, the 'complementarity' hypothesis posits that different color morphs exploit different environmental conditions, allowing mixed-morph pairs to hunt under a wider range of conditions and predicts that food is delivered more consistently. We test these hypotheses using nest cameras to record prey delivery rates during the late nestling phase when both parents are foraging. We found support for the 'complementarity' hypothesis, with mixed-morph pairs delivering food more consistently, but not at a higher rate. The higher consistency in prey deliveries may explain the improved survival of the offspring of mixed-morph pairs, and therefore play a role in maintaining the stability of color-polymorphism in this system.</div