Does the reproductive status of male round gobies (<Emphasis Type="Italic">Neogobius melanostomus</Emphasis>) influence their response to conspecific odours?

While pheromone communication has been well documented in the female round goby, male responses have not been examined. We determined if male round gobies responded to odours of their conspecifics, and whether that response varied with their reproductive status (reproductive and non-reproductive). No significant differences were observed for any treatment (dechlorinated water, or water conditioned by reproductive males (RM) and non-reproductive males (NRM) and females), although RM spent more time inside shelter than NRM (p < 0.05). Morphologically, length and weight did not vary, but gonadosomatic index, seminal vesicle somatic index and relative head width did differ between the two male groups (p = 0.000). Round goby males guard nests in cavities, and so a preference for shelter with increasing reproductive status is expected. Also, a lack of male responses to conspecific odours may be adaptive in this species, since males nest together in high densities, where increased aggression might prove detrimental for nesting males.     

Discovery of a regular nesting area of loggerhead turtle <Emphasis Type="Italic">Caretta caretta</Emphasis> in southern Italy: a new perspective for national conservation

Loggerhead turtle Caretta caretta nesting in Italy had been reported to be limited to the Pelagian Islands and only sporadically elsewhere. As presence of loggerhead turtle nests had occasionally been reported (1988–1999) along about 200 km of the Ionian coast of Calabria, we carried out a project to assess the actual state of the nesting population between 2000 and 2004. We divided the coastline in two sectors (A: 52 km, and B: 146 km) that were monitored from mid-June to end of July for a total of n = 174 monitoring days and 1,813.6 km patrolled on foot with different intensities (extensive versus intensive). In sector B, through extensive monitoring we did not find any emergence tracks, but in sector A by intensive survey (2002–2004: one survey/3.64 days) we detected 3–8 nests/year. In total, 25 nests (both observed and reported), were recorded in our study area, and an assessment of a total of 15–16 nests/year was suggested. These figures, within the national scenario depicted from the review of known nesting events in the last 40 years (88 records concerning more than 143–144 nests), show that loggerhead turtle nesting has been underestimated in Italy, due to inadequate monitoring protocols, and that nesting is more frequent than expected (at least 30–40 nests/year). Conservation strategies in Italy should then focus not only on the reduction of mortality at sea, but also include large-scale actions to preserve scattered (but regular) nesting events.     

Male‐skewed adult sex ratio,survival, mating opportunity and annual productivity in the Snowy Plover Charadrius alexandrinus

Sex differences in adult mortality may be responsible for male‐skewed adult sex ratios and male‐skewed parental care in some birds. Because a surplus of breeding males has been reported in serially polyandrous populations of Snowy Plover Charadrius alexandrinus, we examined sex ratio, early‐season nesting opportunities, adult survival and annual reproductive success of a Snowy Plover population at Monterey Bay, California. We tested the hypotheses that male adult survival was greater than female survival and that a sex difference in adult survival led to a skewed adult sex ratio, different mating opportunities and different annual productivity between the sexes. Virtually all females left chicks from their first broods to the care of the male and re‐nested with a new mate. As a result, females had time to parent three successful nesting attempts during the lengthy breeding season, whereas males had time for only two successful attempts. Among years, the median population of nesting Plovers was 96 males and 84 females (median difference = 9), resulting in one extra male per eight pairs. The number of potential breeders without mates during the early nesting period each year was higher in males than in females. Adult male survival (0.734 ± 0.028 se) was higher than female survival (0.693 ± 0.030 se) in top‐ranked models. Annually, females parented more successful clutches and fledged more chicks than their first mates of the season. Our results suggest that in C. alexandrinus a sex difference in adult survival results in a male‐skewed sex ratio, which creates more nesting opportunities and greater annual productivity for females than for males.     

Lack of costs associated with nest‐related behaviors in an arachnid with exclusive paternal care

Nest‐related behaviors may benefit males by increasing offspring survival and their attractiveness to females, but may also limit males’ foraging activity, increase their metabolic expenses, and expose them to increased mortality during nest attendance. Although intensively studied among birds and ectothermic vertebrates, the costs of nest‐related behaviors in arthropods remain poorly explored. Females of the Neotropical harvestman Zygopachylus albomarginis (Arachnida: Opiliones) lay eggs exclusively inside mud nests that are built, repaired, cleaned and defended by males, which may remain stationary and associated with the nest for up to five months. To assess energetic and survival costs of nest‐related behaviors in this arthropod species, we measured body condition of nesting and non‐nesting males and conducted a field capture‐mark‐recapture study to estimate their survival rates. Despite the long period of nest attendance, nesting males sustained good body conditions and presented higher survival rates than non‐nesting males and females. Two ecological conditions may play an important role modulating the costs of nest attendance in the species. First, high food supply in tropical rainforests may provide males with frequent access to food in the vicinity of their nests, reducing or eliminating the costs related to limited foraging opportunities. Second, predation pressure seems to be directly mostly to vagrant individuals, so that the more they move, the more likely they are to be singled out by predators. Taken together, our findings indicate that nest and offspring defense in Z. albomarginis provide numerous benefits, surprisingly imposing no evident cost to the males.     

Brain and gonadal aromatase activity and steroid hormone levels in female and polymorphic males of the peacock blenny Salaria pavo

In the peacock blenny Salaria pavo large males with well-developed secondary sexual characters establish nests and attract females while small “sneaker” males mimic female sexual displays in order to approach the nests of larger males and parasitically fertilize eggs. These alternative reproductive tactics are sequential, as sneakers irreversibly switch into nesting males. This transition involves major morphologic and behavioral changes and is likely to be mediated by hormones. This study focuses on the role of aromatase, an enzyme that catalyses the conversion of androgens into estrogens, in the regulation of male sexual polymorphism in S. pavo. For this, sex steroid plasma levels and aromatase activity (AA) in gonads, whole brain and brain macroareas were determined in sneakers, transitional males (i.e. sneakers undergoing the transition into nesting males), nesting males and females collected in the field. AA was much higher in ovarian tissue than in testicular tissue and accordingly circulating estradiol levels were highest in females. This supports the view that elevated AA and estradiol levels are associated with the development of a functional ovary. Transitional males are in a non-reproductive phase and had underdeveloped testes when compared with sneakers and nesting males. Testicular AA was approximately 10 times higher in transitional males when compared with sneakers and nesting males, suggesting high AA has a suppressive effect on testicular development. Nesting males had significantly higher plasma levels of both testosterone (T) and 11-ketotestosterone when compared with the other male morphs and previous studies demonstrated that these androgens suppress female-like displays in sneakers. In the brain, AA was highest in macroareas presumably containing hypothalamic nuclei traditionally associated with the regulation of reproductive behaviors. Overall, females presented the highest levels of brain AA. In male morphs AA increased from sneakers, to transitional males, to nesting males in all brain macroareas. These results suggest that the transition into the nesting male tactic is accompanied both by an increase in testicular androgen production and by a higher conversion of androgens into estrogens in the brain. The increase in androgen production is likely to mediate the development of male secondary sexual characters while the increase in brain AA may be related to the behavioral changes associated with tactic transition.     

Long‐term studies on restoration of Connecticut River anadromous sea lamprey,Petromyzon marinus Linnaeus 1758: Trend in annual adult runs,abundance cycle,and nesting

This study is the first to evaluate the results of 60 years of restoring anadromous sea lamprey, Petromyzon marinus, to historical spawning and rearing habitats using fish passage at barrier dams in the Connecticut River, USA. We obtained counts of pre‐spawning adult P. marinus annually passed upstream at Holyoke Dam (river km 140), Connecticut River, MA, during 37 years (1978–2014), and we counted P. marinus nests during 25 years (1986–2010) in the Fort River, a tributary upstream of Holyoke Dam. These two data sets were used to study relationships between adult passage and subsequent nesting and to study nesting timing and ecology. During the 37 years, annual adult P. marinus abundance at Holyoke Dam ranged from 15,000 to 95,000, but regression analysis found no trend (p = .50) for increasing annual adult abundance with years. However, during the 37 years, adults gained access via fish passage at dams to an estimated double the amount of spawning and rearing habitat upstream compared to the 1970s. The lack of a trend for increased adult abundance is consistent with a hypothesis of non‐natal river homing by adults. However, the lack of a trend in adult abundance, when many more larvae are likely present in the watershed compared to the 1970s, is inconsistent with the hypothesis that greater numbers of larvae (and greater concentration of larval pheromone) results in greater number of adults attracted to a river. Instead of an abundance trend of adults with years, we found a rare life history phenomenon occurs in anadromous adult P. marinus ─ an abundance cycle with peaks at 6 year intervals (autocorrelation analysis, p = .04). Comparison of passage timing with nesting timing found passage did not affect nesting initiation or duration (p = .61). Annual date of nesting initiation strongly affected the duration of nesting with earlier nesting resulting in longer nesting (p = .001). Time series comparing Fort River temperature and discharge with nesting found these factors did not clearly predict annual initiation of nesting. This suggests a role for day length (photoperiod) as the trigger for nesting initiation (most nesting began annually during 1–14 June, all year mean, 7 June), regardless of river conditions. However, river discharge may affect nesting ecology because most nesting occurred during decreasing discharge when variability in daily discharge was small (stable discharge). The present research on passage and nesting contributes to a new Connecticut River restoration program for P. marinus, which is a keystone fish species in the watershed.     

Unravelling the evolution of complex reproductive traits with phenotypic engineering

The social dynamics surrounding courtship, mating and parental care are complex enough when just a single male and female are involved, but for species that employ multiple strategies for achieving fertilization success, the network of interactions among rivals, allies and suitors can be utterly complicated. Such is the case in the ocellated wrasse, Symphodus ocellatus, in which males adopt one of three mating strategies. The large, colourful “nesting males” court females, defend territories and care for fertilized eggs until they hatch. The smaller “satellite males” help the nesting males court females and guard against the third morph, the “sneaker males”, which sneak in when a nesting male is spawning with a female and surreptitiously release sperm. Sneaker males perform no courtship displays nor defend territories, so their reproductive investment is devoted entirely to sperm production. And these alternative male strategies work: 100% of nests contain some eggs fertilized by sneaker and satellite males, despite the fact that parental care is solely the responsibility of nesting males In this issue of Molecular Ecology, work to untangle the proximate mechanisms regulating the reproductive physiology of nesting males and their behaviour towards other males, which impacts the entire social network. Moreover, they describe how variation in neuroendocrine regulation can give rise to variation in reproductive traits, upon which sexual selection can act.     

THE BREEDING OF HEUGLIN'S MASKED WEAVER AND ITS NESTING ASSOCIATION WITH THE RED WEAVER ANT

Grimes, L. G. 1973. The breeding of Heuglin's Masked Weaver and its nesting association with the Red Weaver Ant. Ostrich 44: 170–175.

The breeding season of Heuglin “s Masked Weaver Ploceus heuglini at Legon began in the latter half of the major dry season in January and February; continued through the main wet season and ceased in late August and for the rest of the year. The Accra colony had a similar breeding activity but in addition was active for a short period in November which had ended by mid-December. Although the majority of males formed colonies in which the number of males ranged from two to twenty, solitary breeding occurred equally frequently. Most males within the Legon colony, and possibly this is true for all colonies, were polygynous while most solitary males were monogamous. More nests were built by each male than the number of females involved in the polygyny.

A close nesting association with the Red Weaver Ant Oecophylla longinoda existed and the data suggested that the weaver sought the ant. Two cases were found of nesting association with the wasp Belanogaster grisens.     

Nesting habitat characteristics of Marbled Murrelets occurring in near‐shore waters of the Olympic Peninsula,Washington

Marbled Murrelets (Brachyramphus marmoratus) are listed as threatened in the portion of their range extending from British Columbia to California due to loss of nesting habitat. Recovery of Marbled Murrelet populations requires a better understanding of the characteristics of their nesting habitat in this part of their range. Our objective, therefore, was to describe their nesting habitat in Washington State and Vancouver Island, British Columbia. We captured Marbled Murrelets from 2004 to 2008, fitted them with radio transmitters, and followed them to nests (N = 20). We used Cohen's unbiased d effect size to assess differences between forest plots surrounding nest sites and nearby control sites (N = 18). Nest sites had less canopy cover of the dominant conifers and fewer, but larger, trees than control sites. Nest sites also had greater percentages of trees with platforms >10 cm diameter and >15 cm diameter, and more platforms of these sizes than control sites. The mean diameter at breast height of nest trees was 136.5 cm (range = 84–248 cm) and all but one nest was in dominant or co‐dominant tree species. At the landscape scale, we used vegetation maps derived from remotely sensed data and found greater canopy cover, higher density of mature trees, more platforms >10 cm/ha, and more old‐growth habitat at nest sites than at random sites. Our findings suggest that, at the site scale, nesting Marbled Murrelets selected the most suitable features of forest structure across expansive potentially suitable habitat. Our landscape‐scale analysis showed that habitat features in nesting stands differed from those features in available stands in the murrelet's range in Washington. We also found that stands with nests were less fragmented than available forest across murrelet range. All nest sites of radio‐tagged birds in Washington were in protected areas in mostly undisturbed forest habitat. Conservation of these areas of inland nesting habitat will be critical to the recovery of Marbled Murrelet populations.     

The potential for worker reproduction in the ant <Emphasis Type="Italic">Aphaenogaster cockerelli</Emphasis> and its absence in the field

A reproductive division of labor between subordinates and established reproductives is a hallmark of eusociality. In most groups, however, workers retain some reproductive capabilities. Across insect societies, measures of successful worker reproduction in the presence of a queen, with few exceptions, indicate that worker reproduction is kept at very low levels. There are, however, certain colony-level characteristics that may influence the degree to which worker reproduction is promoted, such as queen number, queen mating frequency, and physical presence of a queen in species with multiple nesting sites (polydomy). In this study, the level of worker reproduction in field colonies of the ant species Aphaenogaster cockerelli was measured. A. cockerelli is a monogynous and polydomous species, so worker reproduction across nesting sites was investigated. None of the 297 males sampled provided any evidence of worker reproduction. Worker reproduction would have been detectable if it was present at or above a level of 1.5 % of the total males per colony. An effective mating frequency for queens of this species was found to be 1.03. Although A. cockerelli colonies have many colony-level factors potentially promoting worker reproduction (workers with active, trophic egg-producing ovaries, a single singly-mated queen, workers who are physically separated from the queen), it is evident that worker reproduction is highly regulated. Synthesizing the extensive amount of policing and fertility signaling data previously reported on this species, A. cockerelli is presented as case study for how worker reproduction is repressed and cooperation is maintained in insect societies.     

No short‐ or long‐term effects of geolocator attachment detected in Pied Flycatchers Ficedula hypoleuca

Tracking small passerines using miniaturized location tags is a rapidly expanding field of study. In a 1‐year study, we tested whether there were any short‐ or longer‐term effects of fitting geolocators weighing 3% of body mass on male Pied Flycatchers Ficedula hypoleuca. In the deployment year, we compared adult provisioning rates to nestlings, nestling growth and nest success between nesting attempts in which adult males were fitted with a geolocator, with control nests where males had the same capture history but were not tagged. We found no difference between treatments in provisioning effort by males or their associated female 2 days after geolocator fitting, in terms of nestling growth, subsequent brood reduction or nest success. Return rate, arrival date on territories, nest timing and breeding parameters were compared between tagged and untagged males in the following breeding season. We found no difference in return rate or arrival date, and no difference in nest timing, fecundity or outcome. Our study suggests that fitting lightweight tags to small passerines need not affect behaviour, breeding or apparent between‐year survival. However, tagging new species should still require assessment and comparison with well‐matched control cohorts, and it should be recognized that tag effects could vary between years and populations, mediated by environmental conditions.     

Nest‐site selection by Interior Least Terns and Piping Plovers at managed,off‐channel sites along the Central Platte River in Nebraska,USA

Given the high productivity of Interior Least Terns (Sternula antillarum athalassos) and Piping Plovers (Charadrius melodus) on constructed off‐channel nesting sites along the central Platte River in Nebraska, USA, and the possibility of creating similar habitats at other locations in their breeding range, understanding how these species use off‐channel nesting habitats is important. We used data collected along the central Platte River in Nebraska, USA, over a 15‐year period (2001–2015), and a discrete‐choice modeling framework to assess the effects of physical site attributes and inter‐ and intraspecific associations on off‐channel nest‐site selection by Interior Least Terns and Piping Plovers. We found that Piping Plovers avoided nesting near each other, whereas colonial Interior Least Terns selected nest sites near those of conspecifics. In addition, the relative probability of use for both species was maximized when distance to the nearest predator perch was ≥ 150 m and elevation above the waterline was ≥ 3 m. Probability of use for nesting by Interior Least Terns increased as distance to water increased, whereas the probability of use by Piping Plovers was maximized when distance to water was ~50 m. Our results suggest that important features of constructed, off‐channel nesting sites for both species should include no potential predator perches within 150 m of nesting habitat and nesting areas at least 3 m above the waterline. Efficient site designs for Interior Least Terns would be circular, maximizing the area of nesting habitat away from the shoreline, whereas an effective site design for Piping Plovers would be more linear, maximizing the area of nesting habitat near the waterline. An efficient site design for both species would be lobate, incorporating centralized nesting habitat for Interior Least Terns and increased access to foraging areas for nesting and brood‐rearing Piping Plovers.     

Vocal Behavior During Territorial Intrusions in the Lusitanian Toadfish: Boatwhistles Also Function as Territorial ‘Keep‐Out’ Signals

Male signals are frequently studied in a single behavioral context, but in some cases they may assist multiple functions, namely for both male–male competition and female mate choice. Boatwhistles are known as the mate attraction calls of toadfishes typically produced during the breeding season. However, recent observations with the Lusitanian toadfish Halobatrachus didactylus (Batrachoididae) indicate that the emission of boatwhistles is not restricted to this period, which suggests a function in other behavioral contexts such as agonistic territorial interactions. We experimentally manipulated the social context of toadfish males to investigate whether boatwhistles are produced during territorial defense, by introducing ‘intruders’ in an experimental tank containing nesting ‘resident’ males. Furthermore, we examined whether parental care (eggs in the nest) affected the behavioral responses of resident males during territorial defense. Resident males defended their shelters producing sounds, mostly boatwhistles, towards intruders. Parental males revealed higher aggression levels, exhibiting additional threatening and attack behaviors. Boatwhistles registered during agonistic events were compared with the mate advertising boatwhistles recorded from small aggregations of nesting males in a natural breeding intertidal area. Agonistic boatwhistles were produced in lower and variable calling rates comparing with the advertising ones that were typically emitted in long series of calls. Agonistic boatwhistles were similar in duration and frequency harmonic structure (with a middle tonal phase) to the advertising calls, but presented less amplitude modulation, and lower dominant and fundamental frequencies. These acoustic differences were probably related to differences in calling rates and broadcast demands associated to the distance to the intended receiver. We provide first evidence that, apart from attracting mates, the toadfish boatwhistles also function as active ‘keep‐out’ signals during territorial defense.     

Home sweet home: evidence for nest‐fidelity in the rocky intertidal fish,the shanny Lipophrys pholis

The ability to be faithful to a particular area or site was analysed in the shanny Lipophrys pholis. Using passive integrated transponders, adults from a population of L. pholis at Cabo Raso, Portugal, were followed over a period of 3 years. The findings showed that site fidelity is a consistent behaviour during the breeding season with specific breeding males being found only in particular sectors within the area, and in specific nests throughout the years. The fact that, in general, L. pholis individuals were absent from the study area during the non‐breeding season and breeding males were recorded returning to the same nests and sectors for consecutive breeding seasons suggests that they have developed excellent homing abilities. Translocation data corroborate this idea showing that breeding males successfully returned to their nests after a displacement of >100 m. Altogether, these findings highlight the relevance of life‐history traits (e.g. nesting) in the conditioning of site fidelity and homing for this species of rocky intertidal fish, and more importantly, provide evidence for the need of a well‐developed navigational system.     

Biology of <Emphasis Type="Italic">Lasioglossum</Emphasis> (<Emphasis Type="Italic">L.</Emphasis>) <Emphasis Type="Italic">majus</Emphasis> (Hymenoptera: Halictidae), a largely solitary sweat bee with behavioural adaptations to communality

Within the bee family Halictidae there have been three origins of sociality. Although detection of origins and reversal from sociality requires phylogenetic studies, at a behavioural level a predisposition to sociality can be detected by analysis of intra-specific interactions. We studied aspects of nesting biology and behavioural interactions in Lasioglossum (Lasioglossum) majus, a poorly known halictine inhabiting temperate regions of Europe, which is suspected to be solitary. Nests were found to be largely used by one female, but some were shared by more than one individual. These few nests, whose entrances were very close to each other, were found to be connected underground. A few individuals were observed to enter in a nest where a female was waiting, behaving as a guard and allowing the incoming bee to enter the nest. By use of circle-tube experiments, the behavioural repertoire exhibited by females during encounters was assessed. Levels of withdrawal and cooperative events were comparable with those observed in other solitary nesting species, but aggressive events were very rare, as in several observed communal species. We conclude that L. (L.) majus females, despite general solitary nesting, possess behavioural components enabling them to adopt, probably in high nest-density areas, nest-sharing strategies. A similar kind of local social polymorphism has been observed in two other species of the subgenus Lasioglossum, but these are the first data available on a European species and the first record of subterranean connections among nests of halictid bees.     

Saccular potentials of the vocal plainfin midshipman fish, <Emphasis Type="Italic">Porichthys notatus</Emphasis>

The plainfin midshipman fish, Porichthys notatus, is a vocal species of teleost fish that generates acoustic signals for intraspecific communication during social and reproductive behaviors. All adult morphs (females and males) produce single short duration grunts important for agonistic encounters, but only nesting males produce trains of grunts and growls in agonistic contexts and long duration multiharmonic advertisement calls to attract gravid females for spawning. The midshipman fish uses the saccule as the main acoustic endorgan for hearing to detect and locate vocalizing conspecifics. Here, I examined the response properties of evoked potentials from the midshipman saccule to determine the frequency response and auditory threshold sensitivity of saccular hair cells to behaviorally-relevant single tone stimuli. Saccular potentials were recorded from the rostral, medial and caudal regions of the saccule while sound was presented by an underwater speaker. Saccular potentials of the midshipman, like other teleosts, were evoked greatest at a frequency that was twice the stimulus frequency. Results indicate that midshipman saccular hair cells of non-reproductive adults had a peak frequency sensitivity that ranged from 75 (lowest frequency tested) to 145 Hz and were best suited to detect the low frequency components (≤105 Hz) of midshipman vocalizations.     

Mating success in brood-guarding male rock bass,Ambloplites rupestris: the effect of body size

Synopsis The hypothesis that variation in a paternal trait associated with offspring survival will result in female mate choice based on that trait was tested in rock bass,Ambloplites rupestris, a temperate fresh water fish with uniparental male care. The number of eggs acquired by 108 nesting male rock bass, in Cranberry Lake (New York State, U.S.A.), was estimated in two different spawning episodes that differed in the size structure of the nesting male stock. Early breeders (between the 4–7 June 1989) were mainly medium and large males (101–300 g), as compared to late breeders (between the 19–21 June 1989) which were mostly small (50–100 g). Because survival of larvae in rock bass is significantly lower in nests guarded by small males as compared to nests guarded by medium and large males, it was hypothesized that female mate choice should have been (1) size-based, and (2) more intense late in the season when the nesting stock was comprised mostly of small males. The results were consistent with these hypotheses. Variation in egg numbers per nest was significantly higher during the late spawning episode. In addition, egg number per nest were normally distributed during the early spawning episode, but were positively skewed and leptokurtic during the later episode. The correlation between male size and egg number was significant for both spawning episodes. However, during the late episode male size explained 23% of the variation in egg numbers versus only 8% of the variation during the earlier episode.     

Escape to the high canopy—thermal deficiency causes niche expansion in a forest‐floor ant

The small formicoxenine ant Temnothorax saxonicus was known from about 40 localities in Central Europe nesting in anorganic substrates on floor of xerothermous forests whereas investigations of 198 tree canopies in 19 forest sites of the same region provided no indication for arboreal nesting or foraging. We present the first evidence for canopy‐nesting populations of T. saxonicus on old Quercus trees in 3 sites having maximum calibrated topsoil temperatures of 17.9 ± 0.3 °C which were significantly (P < 0.007) lower than 22.8 ± 2.0 °C measured in 5 sites with ground‐nesting populations. The thermal deficit on forest floor inhibits brood development in ground nests and caused a moving to canopy were maximum calibrated temperatures of the, now wooden, substrates are at least 26.1 °C for the whole canopy and 30.8 °C in more sun‐exposed spots. T. saxonicus competed here successfully with the obligatory canopy ants T. affinis and T. corticalis. The distributional data of this rope‐climbing study support former results that highest nest densities of small arboreal ants occur in temperate climate over the entire canopy mantle of single trees situated in open land or in park‐like environments but occur in the top of the canopy in tree stands with high degree of canopy closure.     

Sex differences in nest defence by the red-backed shrike<Emphasis Type="Italic"> Lanius collurio</Emphasis>: effects of offspring age,brood size,and stage of breeding season

The red-backed shrike Lanius collurio is an open-cup nesting passerine bird, which protects its nest aggressively attacking predators near the nest. The response of parents to a human observer was investigated during the nesting period 1999–2001 in Poland. The intensity of nest defence increased as the breeding cycle progressed in accordance to the offspring value hypothesis. However, we did not find an increase in the level of aggression according to the number of offspring and the time of season. Contrary to previous predictions, we did not find gender differences in nest defence. More aggressive parents, both females and males, have significantly better breeding success than quieter individuals.