Host activity and the risk of nest parasitism by brown-headed cowbirds

Proportions of nests parasitized by brown-headed cowbirds (Molothrus ater) vary greatly among host species, but factors underlyingthis variation remain poorly understood. Cowbirds are believedto find nests by watching host behavior. We tested the hypothesisthat the activity of hosts during nest building correlateswith the probability of parasitism among and within four sympatrichosts: dusky flycatchers (Empidonax oberholseri), warblingvireos (Vireo gilvus), yellow warblers (Dendroica petechia),and American redstarts (Setophaga ruticilla). Daily probabilityof parasitism varied substantially among these species, from3% for dusky flycatchers to more than four times that for warblingvireos. The four species did not differ in the proportion ofcowbirds fledged from their nests. Differences in nest placementdid not explain differences in probability of parasitism amongor within species. Parasitism frequencies increased among speciesthat made longer nest-building visits, had a greater propensityto perch during nest approach, spent more time near their nests,and had males that vocalized more often near nests. Within species, females that visited their nests less often, spent more timeon the nest per visit, and males that sang more and were activein a smaller area around their nests were more likely to beparasitized by cowbirds. These data support the hypothesisthat cowbirds use the activity of hosts during nest buildingto locate nests.     

CULTURAL INHERITANCE AS A MECHANISM FOR POPULATION SEX-RATIO BIAS IN REPTILES

Abstract.— Although natural populations of most species exhibit a 1:1 sex ratio, biased sex ratios are known to be associated with non‐Mendelian inheritance, as in sex‐linked meiotic drive and cytoplasmic inheritance (Charnov 1982; Hurst 1993). We show how cultural inheritance, another type of non‐Mendelian inheritance, can favor skewed primary sex ratios and propose that it may explain the female‐biased sex ratios commonly observed in reptiles with environmental sex determination (ESD). Like cytoplasmic elements, cultural traits can be inherited through one sex. This, in turn, favors skewing the primary sex allocation in favor of the transmitting sex. Female nest‐site philopatry is a sex‐specific, culturally inherited trait in many reptiles with ESD and highly female‐biased sex ratios. We propose that the association of nest‐site selection with ESD facilitates the maternal manipulation of offspring sex ratios toward females.     

Botanical and Topographical Factors Influencing Nesting-Site Selection by Chimpanzees in Kalinzu Forest,Uganda

We examined the relative importance of various botanical and topographical factors that influence nesting-site selection by chimpanzees ( Pan troglodytes schweinfurthii) in the Kalinzu Forest of Uganda. All of them—vegetation type; topographical features; frequency of preferred tree species; frequency of preferred tree size; fruit abundance—significantly influenced nesting-site selection. Fruit abundance and vegetation type had much stronger influences on site selection than the other factors did. In a dense forest environment like the Kalinzu Forest, the local and seasonal distributions of chimpanzee nests seem to reflect the pattern of home range use for feeding.     

Orangutan Nesting Behavior in Disturbed Forest of Sabah,Malaysia: Implications for Nest Census

High concentrations of orangutans remain in the multiple-use forests of the Lower Kinabatangan, Sabah, Malaysia. Compared to primary forest, the habitat is highly fragmented, characterized by a low tree density (332 stems/ha), small tree size (83.6% of trees are <20 m high), low basal area (18 m²/ha), abundance of canopy gaps and high level of soil disturbance. The forest structure and composition influence orangutan nesting patterns, and thus directly influence the results of nest surveys used to determine orangutan population size. In logged forests, tall and large trees are the preferred nesting sites of orangutans. The scarcity of suitable nesting sites in the logged-over forests of Kinabatangan, could partly explain the lower daily rate of nest construction (r = 1.00) versus those of other orangutan populations. The nest decay rate t recorded at the study site (average ± SD = 202 ± 151 days) strongly depends on the species of tree in which a nest is built. Our results illustrate that the nest-related parameters used for orangutan censuses fluctuate among habitat types and emphasize the need to determine specific values of r for specific orangutan populations and of t for different tree species in order to achieve accurate analysis of census data.     

浙江五峙山列岛黄嘴白鹭的巢位选择研究

黄嘴白鹭(Egretta eulophotes)是全球性受威胁鸟类。2005年7月, 我们在浙江五峙山列岛对黄嘴白鹭的巢位选择进行了研究, 共测量了74个巢。研究发现, 在0.99 hm2的馒头山小岛上, 黄嘴白鹭的巢呈聚集性分布, 平均巢间距为119.6 cm, 最小巢间距为15 cm。黄嘴白鹭对巢位具有明显的选择性, 优先选择在灌丛, 尤其是那些相对较高的灌丛(高于50 cm)下营巢, 其次是较低的灌木(低于64 cm)内部和草丛上。多数巢存在遮蔽物。避风和遮荫是黄嘴白鹭巢位选择的主要要求。台风是决定五峙山列岛黄嘴白鹭巢位选择的最主要因素, 而高灌木的数量直接影响五峙山列岛黄嘴白鹭的繁殖成功和今后的资源状况。     

Conformity to Bergmann's rule in birds depends on nest design and migration

Ecogeographical rules attempt to explain large‐scale spatial patterns in biological traits. One of the most enduring examples is Bergmann''s rule, which states that species should be larger in colder climates due to the thermoregulatory advantages of larger body size. Support for Bergmann''s rule, however, is not consistent across taxonomic groups, raising questions about what factors may moderate its effect. Behavior may play a crucial, yet so far underexplored, role in mediating the extent to which species are subject to environmental selection pressures in colder climates. Here, we tested the hypothesis that nest design and migration influence conformity to Bergmann''s rule in a phylogenetic comparative analysis of the birds of the Western Palearctic, a group encompassing dramatic variation in both climate and body mass. We predicted that migratory species and those with more protected nest designs would conform less to the rule than sedentary species and those with more exposed nests. We find that sedentary, but not short‐ or long‐distance migrating, species are larger in colder climates. Among sedentary species, conformity to Bergmann''s rule depends, further, on nest design: Species with open nests, in which parents and offspring are most exposed to adverse climatic conditions during breeding, conform most strongly to the rule. Our findings suggest that enclosed nests and migration enable small birds to breed in colder environments than their body size would otherwise allow. Therefore, we conclude that behavior can substantially modify species’ responses to environmental selection pressures.     

Benefits of communal breeding in burying beetles: a field experiment

1. The ultimate causes of communal breeding and joint parental care in various species of Nicrophorus burying beetles have not been resolved satisfactorily. One hypothesis suggests that females remain on the carcass for extended periods of time because joint defence affords them improved probabilities of retaining the carcass successfully in the face of intense competition from intra‐generic competitors. 2. In a field experiment designed to test this hypothesis in N. defodiens (Mannerheim), breeding associations of two females and a male were no more successful at retaining their carcass than were monogamous pairs, lending no support to the hypothesis. 3. Intra‐generic intruders that usurped already‐buried carcasses were typically much larger than the original residents. 4. The body size of original residents affected both the burial depth and the probability of a takeover. Larger beetles buried the carcass deeper and were more likely to retain possession of the carcass. Group composition also did not affect the depth at which carcasses were buried. 5. Severe and even fatal injuries incurred by some residents indicated the occurrence of violent and damaging fights between competitors over carcasses in the field.     

布氏田鼠越冬集群贮草面积的两种估算方法比较

布氏田鼠 (Ｍｉｃｒｏｔｕｓｂｒａｎｄｔｉ)为内蒙古典型草原区的主要害鼠 ,具贮草越冬习性[2 ,5～ 7] 。因此 ,研究其越冬集群的贮草面积 ,对于分析该鼠的越冬生态特征以及定量衡量其危害程度 ,具有重要的意义。本文提出两种估算布氏田鼠越冬集群贮草面积的方法 ,即黄蒿根计数法和跑道测量法 ,并对两种估算方法进行了比较。1　材料与方法本项研究是于 1 995年度在内蒙古赤峰市克什克腾旗阿其乌拉苏木 ( 1 1 6°2 5′Ｎ ,37°5 1′Ｅ)以及中国科学院内蒙古草原生态系统定位研究站 ( 43°37′Ｎ ,1 1 6°4 1′Ｅ)进行的。1 0月中旬 ,在阿其…