Effects of experimental food provisioning on reproduction in the Jackdaw Corvus monedula, a semi‐colonial species (original) (raw)
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Sex-specific hatching order, growth rates and fledging success in jackdaws Corvus monedula
Journal of Avian Biology, 2003
In the jackdaw Cor6us monedula, eggs hatch asynchronously with the youngest chicks in the brood often starving to death. So far, it is unknown whether there are sex differences in vulnerability to starvation. Adult females are smaller than males suggesting that daughters should be cheaper to produce than sons and so, less likely to starve when nest conditions are poor. Here, we determine whether sex, laying order and season interact to influence growth and fledging success. In a nestbox population of jackdaws, we found a non-significant female bias at both hatching (112:120) and fledging (37:52). Generalised linear models revealed that parents seemed to be investing differently in sons and daughters depending on their chances of success. Broods produced late in the season were significantly female biased, particularly those from small clutches. Females hatched towards the end of the season, when conditions were poor, were more likely to fledge than males. Nestlings that were relatively large at hatching were more likely to fledge. This effect was particularly important for last hatched individuals. Overall, males had a higher mortality rate than females. The most likely cause was starvation due to higher energetic requirements, because males were larger than females at fledging. We suggest that in species with brood reduction, sex-biased mortality may be at least as important as primary sex ratio manipulation in determining avian sex ratios.
Colonial breeding reduces nest predation in the common gull (Larus canus)
Animal Behaviour, 1984
It is often suggested that colonial breeding reduces nest predation for birds with a high defence capacity, but experimental comparison of predation at solitary and colonial nests is seldom feasible within a single species. We here report on such a test in the common gull (Larus canus). The rate of predation on experimental eggs was significantly lower near colonies than near solitary gull nests, and the eggs survived longer at the edge of a colony than farther away. Communal mobbing of nest predators is the likely reason. In both of two years, almost all nests of solitary gulls were destroyed by predators, while most clutches survived in colonies. Nest predation hence selects strongly for colonial breeding in the present population of common gulls.
Effect of supplemental feeding on nesting success in the Lesser Kestrel (Falco naumanni)
Israel Journal of Ecology and Evolution, 2019
The effect of food supplement to Lesser Kestrel (Falco naumanni) nests during the nestling period (from hatching to fledging) was studied in two nesting colonies in Israel – Alona and Jerusalem. Our hypothesis, based on diminishing returns considerations, was that food supplement will have a greater effect on fledgling success in the food-limited, urban colony of Jerusalem, than in the rural colony of Alona. Indeed, food supplement had a significantly positive effect on breeding success in both colonies. However, and contrary to our prediction, the decrease in chick mortality between supplemented and control nests in Jerusalem was not larger than in Alona (actually it was numerically smaller, albeit not significantly so). This implies either that additional factors, possibly urbanization associated, other than food limitation, might be responsible for the difference in nesting success of Lesser Kestrels between Alona and Jerusalem, and/or that the amount or the nutritional quality o...
Effects of Cowbird Parasitism on Parental Provisioning and Nestling Food Acquisition and Growth
The Condor, 1998
Brood parasitism by Brown-headed Cowbirds (Molothrus ater) is known to affect tbe fitness of many hosts by causing a reduction in the number of chicks that fledge from parasitized nests. However, little is known about less immediate effects on host fitness. We studied nestling growth and food acquisition and parental provisioning in parasitized and unparasitized nests of the Indigo Bunting (Passerina cyanea). Indigo Bunting nestlings in parasitized nests exhibited reduced rates of mass gain, but not tarsus growth, relative to bunting chicks in unparasitized nests. Bunting nestlings in parasitized nests received less food than did buntings in unparasitized nests. Buntings in parasitized nests spent more time begging than did those in unparasitized nests, but energy expended in this behavior may not have detracted greatly from the amount of energy available for growth. Adults at parasitized nests exhibited a higher provisioning rate than those at unparasitized nests. Increased provisioning by adult buntings at parasitized nests did not come at the expense of time spent brooding nestlings, but increased provisioning has the potential to affect the survival and future reproductive success of host adults. Because cowbird parasitism appears to impose substantial costs on Indigo Bunting nestlings and adults, concern over the conservation implications of parasitism should not be limited to species that suffer total reproductive failure when parasitized.
A study on the nesting biology of the House Crow Corvus splendens was conducted at Hazara University, Garden Campus (50 hectares), Mansehra, during the 2013 breeding season (June to September). Details about nest locations, tree characteristics, nest and egg characteristics were recorded. The mean nest density of House Crow was 0.9 nests/ ha. Mean tree and nest heights were 14.8±6.30 and 11.8±5.42m. The mean tree canopy spread 9.5±2.48m. The mean maximum and minimum nest diameters were 42.3±2.08 and 39.0±1.73cm respectively, while maximum and minimum diameters of nest cup were 15.6±1.52 and 13.3±1.15cm respectively. Nest depth and nest cup depths were measured as 19.3±2.08 and 8.3±1.15cm respectively. The mean nest weight was 1.4±0.24 kg while the mean clutch size was 4.0 (range 1-6). The mean egg length was 38.6±0.69mm, breadth 26.0±0.69mm, egg volume 13.3±0.83cm 3 and egg shape index 1.42±0.83. The mean egg weight was 12.3±0.70g. Egg and nest success were calculated to be 55.1% and 69.0%. Hatchlings and fledglings produced per nest were 2.20 and 1.44 respectively. The main reasons for reproductive failures were unhatched eggs, poor nest construction, bad weather conditions and observer's disturbance.
The Auk, 2018
Predation is a key factor in the nesting preferences of birds. Studies indicate that cavity-breeding birds prefer deeper nest sites, possibly because they are more safe from predation. We studied the Blue Tit (Cyanistes caeruleus), a cavitybreeding passerine, to test (1) whether nest-site depth affects breeding success and (2) whether potential effects of nest-site depth on breeding success are related to predation risk. We performed 2 experiments to separate effects of nest-box depth from potential effects of the quality of the breeding pair. In the first (free-choice) experiment, Blue Tits competed for scarce deep nest boxes that were provided well before nest-box choice, enabling an association between nest-box quality and bird quality. In the second (forced-choice) experiment, we randomly altered nest-box depth after Blue Tits had chosen a nest box, thus disconnecting the association between nest-box quality and bird quality. We found no evidence that the occurrence of signs of predation was related to nest-box depth. However, we did find clear positive effects of nest-box depth (1) on clutch size and hatching success throughout the study area and (2) on fledging success, the number of fledglings, and the overall probability of nest success, specifically in parts of the study area with high predation. We found no indication of independent effects of parental quality on breeding success. Parents also seemed to perceive the shallower boxes as more risky; in shallower boxes, nest thickness was decreased, irrespective of the local predation pressure during the free-choice experiment. Parents nesting in shallow boxes may have had lower breeding success because of (1) increased actual (but undetected) predation and (2) reduced reproductive investment by parents, based on the latter's experience with predation or an evolutionary response to past predation risk.