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Mean Clutch Size (mean + clutch_size)
Selected AbstractsBreeding success in a Houbara Bustard Chlamydotis [undulata] macqueenii population on the eastern fringe of the Jungar Basin, People's Republic of ChinaIBIS, Issue 2 2002O. Combreau Nesting success and chick survival of a migratory population of Houbara Bustard Chlamydotis [undulata] macqueenii were studied during three consecutive years (1998,2000) in the Xinjiang province of north-west China. A total of 45 nests was monitored and 85 broods comprising 227 chicks were captured, of which 82 chicks were radio-tracked. Start of laying varied between 6 and 17 April between years but the laying mode fell consistently between 26 and 30 April. Mean clutch size was 4.0 (sd = 0.8) (range 2,6) for early clutches and 3.3 (sd = 1.1) for late clutches (range 2,5). The average nesting success was 0.588 (sd = 0.270) but great variations were observed between years ,0.882 in 1998, 0.530 in 1999 and 0.351 in 2000. This was related to increased predation in 1999 and 2000, which is reflected by increased predator density (chiefly Corsac Fox Vulpes corsac and Long-legged Buzzards Buteo rufinus). The overall hatchability, defined as the proportion of eggs hatched in successful nests was 0.839 sd = 0.238). The average brood size at hatching varied from 2.9 (sd = 0.8) to 3.3 (sd = 0.9) according to years, and no significant decrease in brood size was observed in the first 5 days post-hatching. In 1999 and 2000 the brood size diminished sharply (14% and 27%, respectively) in prefledging chicks. A further severe decrease (37%) was observed in fledglings in 2000, probably due to predation by raptors. For the 3 years of the study, a successful female Houbara would bring on average 2.3 (sd = 0.9) chicks to fledging and would have lost 30.2% (sd = 14.9%) of its brood to adversity during the rearing process. The proportion of females that lost their entire brood was 0.181 in 1998, 0.708 in 1999 and 0.453 in 2000. For the 3 years of the study, only 55.3% (sd = 26.3%) of the females hatching eggs brought chicks to fledging. The overall chick production was 0.827 per breeding female per year and the probability of an egg laid producing a fledgling of 8 weeks old was 0.190. [source] Life on a limb: ecology of the tree agama (Acanthocercus a. atricollis) in southern AfricaJOURNAL OF ZOOLOGY, Issue 4 2002Leeann T. Reaney Abstract One hundred and sixty-four museum specimens of the tree agama Acanthocercus a. atricollis were measured and dissected to examine sexual size dimorphism, reproduction and diet. Foraging mode and behaviour were also quantified in a wild population to obtain a broader picture of their foraging ecology and to test the hypothesis that tree agamas are ambush foragers. Males and females did not differ significantly in snout,vent length (SVL) or tail length; however, mature males had larger heads than females of the same body size. The smallest female showing sexual maturity was 96 mm SVL and the smallest male was 82 mm SVL. Mean clutch size was 11.3 and was positively correlated with female body size. Reproduction was seasonal and male and female reproductive cycles were synchronous. Testicular volume was greatest during August,September and females contained enlarged follicles during August,December and showed no evidence of multiple clutching. Tree agamas fed on a broad spectrum of arthropods (10 orders), including millipedes, which other lizard taxa have been reported to avoid. Gut contents were dominated numerically by ants (92%), followed by beetles (4%). Volumetrically, orthopterans (26.8%) were most important, followed by beetles (26.3%) and ants (17.9%). Compared to adults, juvenile diet by volume was dominated by ants and consisted of fewer large prey items (e.g. beetles and orthopterans). Seasonal effects in both prey diversity and volume were evident. Tree agamas are classic ambush foragers. They spent only 4% of their time moving and made few movements per minute (mean = 0.4). When stationary, adult tree agamas positioned themselves on tree trunks (34.7%), on lateral branches (41.8%) and occasionally, on the ground (23.4%). No evidence of trophic partitioning (intraspecific niche divergence hypothesis) was found and field observations revealed that males defend territories and engage in combat. This supports the idea that selection may be favouring larger head size in males, as an outcome of male contest competition. [source] Do voles make agricultural habitat attractive to Montagu's Harrier Circus pygargus?IBIS, Issue 3 2007BEN J. KOKS Loss and degradation of habitat threatens many bird populations. Recent rural land-use changes in the Netherlands have led to a shift in habitat use by breeding Montagu's Harriers Circus pygargus. Since the 1990s, unprecedented numbers of this species have bred in farmland compared with numbers in natural habitat. Destruction of nests by agricultural operations, however, compromises breeding success. Between 1992 and 2005, the number of breeding pairs in the northeastern Netherlands was positively, though weakly, correlated with previous-year estimated abundance of voles, mostly Microtus arvalis. In good vole years, the onset of laying was earlier and mean clutch size was larger. Vole abundance was relatively higher in set-aside land and in high and dense vegetation. We suggest that agri-environmental schemes aimed at increasing the availability of voles in agricultural breeding areas may be an effective management tool for the conservation of Montagu's Harriers in the northeastern Netherlands. [source] Molecular determination of paternity in a natural population of the multiply mating polygynous lizard Eulamprus heatwoleiMOLECULAR ECOLOGY, Issue 3 2002S. F. Morrison Abstract We studied the mating system of the southern water skink, Eulamprus heatwolei, during spring and summer (encompassing the breeding season) in a population in southeastern Australia. We examined potential attributes that might influence the mating system and male reproductive success including home range size, physical proximity of adults and body size, and then genotyped all mothers, offspring and potential sires. Home range overlap of both sexes was extensive, with adult females sharing the greatest amount of space with each other and adult males the least amount of space with each other. However, not all adults hold home ranges. We classified approximately one quarter of adult males as home range holders and the rest as ,floaters'. Adult females occupy home ranges more than males, with approximately three-quarters classified as home range holders. Home range ownership is not correlated with body size for either sex, however, male body size is positively correlated with the number of adult female home ranges that his home range overlaps and adult male home ranges are larger than those of females. We used microsatellite genotyping to assign paternities to 55 offspring from 17 litters and then compared this data with our home range and behavioural observations. This species displays extreme levels of multiple paternity given the small mean clutch size of three. Multiple paternity was confirmed in 11 (64.7%) of 17 clutches but three other clutches (for a total of 82.4%) also may display multiple paternity. A total of 30 offspring from 12 litters were assigned to 10 of the 32 genotyped adult males from our study site. Of these 10 adult males, half were home range holders. Five complete clutches and a total of 25 out of the 55 offspring could not be positively assigned to any male surveyed as part of the study and were attributed to floater males or resident males adjacent to our study site that had not been genotyped. While sample sizes are small, neither male home range ownership nor body size is significantly correlated with the number of paternities a male obtained. Our study suggests a polygynous mating system for this species. [source] Climate warming and reproduction in Chinese alligatorsANIMAL CONSERVATION, Issue 2 2009F. Zhang Abstract The Chinese alligator Alligator sinensis is a critically endangered species endemic to China, and one of the most endangered crocodilian species in the world. Like many other reptiles, important aspects of alligator biology such as foraging, timing of hibernation, breeding and the sex ratio of offspring are all affected by temperature variation. We examined the effects of long-term temperature change on oviposition dates and clutch sizes of the Chinese alligator in a semi-natural facility in southern China. Our study focused on two captive generations including an old breeding generation captured from the wild and a generation composed of their F1 offspring. Median oviposition date shifted to earlier in the year and mean clutch size was larger for both generations as the monthly mean air temperature in April increased over the 19 years of data collection. We observed a mean advance in oviposition date of 10 days for the old breeding generation from 1987 to 2005 and 8 days for both generations from 1991 to 2005. Correspondingly, clutch sizes for the two generations also increased during this period. There were no differences in median oviposition dates and clutch sizes between the two generations from 1991 to 2005. Our results suggest that Chinese alligators have responded to increasing global temperatures. Our findings also suggest that recent increasing global temperatures have the potential to have a substantial effect on Chinese alligator populations in the wild, thus prompting an urgent need for field monitoring of the effects of global warming on this endangered alligator species. [source] | ||||||||||