Mélanie F. Guigueno

Nest sanitation in passerine birds: implications for egg rejection in hosts of brood parasites

We reviewed information on nest sanitation (nest cleaning) by passerine birds because the act of cleaning nests is thought to be associated with egg rejection by hosts of brood parasites, and yet there has been no synthesis of the literature on nest sanitation. In the first part of the review, we summarized information on nest sanitation. We found that birds remove a variety of objects from nests such as egg shells, fecal sacs, pieces of vegetation, invertebrate parasites, dead chicks, uneaten food, and occasionally unhatched eggs. Fecal sac removal, the most commonly considered type of nest sanitation behavior, is not divided equally between the sexes across species; females remove more fecal sacs than males. In addition, larger species tend to carry fecal sacs farther than smaller species. In the second part of the review, we discuss the importance of nest sanitation in the evolution of egg rejection behavior of brood parasite hosts. Recent studies involving the experimental addition of non-egg-shaped objects to nests or to the vicinity of nests suggest that nest sanitation plays a role in host rejection of avian brood parasitism. Most objects added to nests prior to hatching (usually hard) and after hatching (usually soft) were rejected. In a logistic regression model, shape and size were the significant factors in eliciting rejection for all hosts that received experimental non-egg objects added to their nests prior to hatching. Nest sanitation may be an exaptation for antiparasite defences and thus plays an important role in the host-parasite arms race.ZusammenfassungWir überprüften Daten zur Nesthygiene (Nestsäuberung) bei Singvögeln. Es wird angenommen, dass Nestsäuberung assoziiert ist mit der Zurückweisung von Eiern durch Wirte von Brutparasiten. Bislang gibt es jedoch keine Synthese der Literatur zur Nesthygiene. Daher fassen wir im ersten Teil der Arbeit die vorhandenen Informationen zur Nesthygiene zusammen. Wir fanden heraus, dass Vögel eine Vielzahl von Objekten aus ihren Nestern entfernen, beispielsweise Eierschalen, Kotpakete, Vegetationsteile, wirbellose Parasiten, tote Küken, Futterreste und gelegentlich nicht geschlüpfte Eier. Die Beseitigung von Kotpaketen, das am meisten beobachtete Nesthygieneverhalten, wird von den Geschlechtern nicht gleichverteilt durchgeführt. Weibchen entfernen mehr Kot aus den Nestern als Männchen. Darüber hinaus tendieren größere Arten dazu, Kotreste weiter weg zu bringen als kleinere Arten. Im zweiten Teil der Studie diskutieren wir die Bedeutung von Nesthygiene in der Evolution des Verhaltens der Gelegeablehnung durch Wirtsarten für Brutparasiten. Aktuelle Studien, bei denen experimentell nicht eierschalenförmige Objekte in die Nester oder in deren Nähe gelegt worden sind, deuten an, dass für die Wirtsarten Nesthygiene eine Rolle spielt bei der Vermeidung von Brutparasitismus durch andere Vogelarten. Die meisten Objekte, die vor (normalerweise harte) und nach dem Schlupf (normalerweise weiche) den Nestern hinzugefügt wurden, werden entfernt. In einem logistischen Regressionsmodell sind Form und Größe die entscheidenden Faktoren für die Zurückweisung der Eier durch die Wirtsvögel, deren Nestern vor dem Schlupf nicht-eierförmige Objekte hinzugefügt worden sind. Nesthygiene könnte eine besondere Anpassung (Exaptation) für Parasitenabwehr darstellen und spielt daher eine bedeutende Rolle in der Beziehung zwischen Wirt und Parasit.

Female cowbirds have more accurate spatial memory than males

Brown-headed cowbirds (Molothrus ater) are obligate brood parasites. Only females search for host nests and they find host nests one or more days before placing eggs in them. Past work has shown that females have a larger hippocampus than males, but sex differences in spatial cognition have not been extensively investigated. We tested cowbirds for sex and seasonal differences in spatial memory on a foraging task with an ecologically relevant retention interval. Birds were trained to find one rewarded location among 25 after 24 h. Females made significantly fewer errors than males and took more direct paths to the rewarded location than males. Females and males showed similar search times, indicating there was no sex difference in motivation. This sex difference in spatial cognition is the reverse of that observed in some polygynous mammals and is consistent with the hypothesis that spatial cognition is adaptively specialized in this brood-parasitic species.

Spatial and temporal trends in brominated flame retardants in seabirds from the Pacific coast of Canada

Polybrominated diphenyl ethers (PBDEs) and hexabromocyclododecane (HBCDD) are bioaccumulative flame retardants. PBDEs increased in many ecosystems during the late 20th century, but recently have declined in some environments. To examine trends in the northern Pacific, we analysed PBDEs, HBCDD and carbon and nitrogen stable isotopes (δ13C and δ15N) to account for dietary effects in archived eggs of three seabird species from British Columbia, Canada, 1990-2011 (rhinoceros auklets, Cerorhinca monocerata; Leachs storm-petrels, Oceanodroma leucorhoa; ancient murrelets, Synthliboramphus antiquus, 2009 only). PBDEs increased until approximately 2000 and then decreased, while HBCDD increased exponentially throughout the examined period. No significant changes in dietary tracers were observed. HBCDD and ΣPBDE levels varied among species; ΣPBDE also varied among sites. Temporal changes in contaminant concentrations are unlikely to have been caused by dietary changes, and likely reflect the build-up followed by decreases associated with voluntary phase-outs and regulations implemented in North America to control PBDEs.

Clutch Abandonment by Parasitized Yellow Warblers: Egg Burial or Nest Desertion?

Abstract. In response to brood parasitism by the Brown-headed Cowbird (Molothrus ater), some female Yellow Warblers (Dendroicapetechia) bury cowbird eggs and sometimes their own eggs, whereas other females desert parasitized nests and renest at new sites. We identified circumstances that elicit burial or desertion by analyzing the histories of 132 naturally parasitized nests inspected over 13 breeding seasons in Manitoba. Damaged nests and clutches reduced to zero, one, or two host eggs were deserted, whereas the clutch was buried when zero, one, or two host eggs were present the morning cowbirds laid and the probability of hatching was high. Response times for burial (2.3 ± 0.1 [SE] days) and desertion (2.5 ± 0.3 days) were similar, but the variance differed significantly (1.29 days2 for burial versus 2.58 days2 for desertion). Burial is the Yellow Warblers more frequent method of rejection, though desertion is used about one-third of the time, and it may be elicited by factors unrelated to brood parasitism, such as interference by predators and inclement weather.

Determining Seabird Body Condition Using Nonlethal Measures

Energy stores are critical for successful breeding, and longitudinal studies require nonlethal methods to measure energy stores (“body condition”). Nonlethal techniques for measuring energy reserves are seldom verified independently. We compare body mass, size-corrected mass (SCM), plasma lipids, and isotopic dilution with extracted total body lipid content in three seabird species (thick-billed murres Uria lomvia, all four measures; northern fulmars Fulmarus glacialis, three measures; and black-legged kittiwakes Rissa tridactyla, two measures). SCM and body mass were better predictors of total body lipids for the species with high percent lipids (fulmars; ) than for the species with low percent lipids (murres and kittiwakes; ). The relationship between SCM and percent body lipids, which we argue is often a better measure of condition, was also poor () for species with low lipids. In a literature comparison of 17 bird species, percent lipids was the only predictor of the strength of the relationship between mass and total body lipids; we suggest that SCM be used as an index of energy stores only when lipids exceed 15% of body mass. Across all three species we measured, SCM based on the ordinary least squares regression of mass on the first principal component outperformed other measures. Isotopic dilution was a better predictor of both total body lipids and percent body lipids than were mass, SCM, or plasma lipids in murres. Total body lipids decreased through the breeding season at both sites, while total and neutral plasma lipid concentrations increased at one site but not another, suggesting mobilization of lipid stores for breeding. A literature review showed substantial variation in the reliability of plasma markers, and we recommend isotopic dilution (oxygen-18, plateau) for determination of energy reserves in birds where lipid content is below 15%.

Brominated flame retardant trends in aquatic birds from the Salish Sea region of the west coast of North America, including a mini-review of recent trends in marine and estuarine birds

Polybrominated diphenyl ethers (PBDEs) increased in many matrices during the 1990s and early 2000s. Since voluntary restrictions and regulations on PBDEs were implemented in North America circa early 2000s, decreases in PBDEs have occurred in many of these same matrices. To examine temporal trends in the North Pacific, we retrospectively analysed PBDEs and eight non-PBDE flame retardants (FR) in eggs of two aquatic bird species, great blue herons, Ardea herodias, and double-crested cormorants, Phalacrocorax auritus, collected along the British Columbia coast, Canada from 1979 to 2012. Increasing PBDE concentrations were observed in both species followed by significant decreases post-2000 for all dominant congeners and ΣPBDE. Non-PBDE FRs were generally undetected in cormorant eggs, or detected at very low levels in heron eggs, except for hexabromocyclododecane (HBCDD). HBCDD, currently unregulated in North America, was not detected in early sampling years; however low concentrations were observed in both species in recent sampling years (2003-2012). Dietary tracers (δ(13)C and δ(15)N) did not change significantly over time, indicating that temporal changes in PBDEs are likely caused by implemented regulations. A comparison with recently published temporal trends of ΣPBDE in marine birds from North America and Europe is given.

Factors influencing legacy pollutant accumulation in alpine osprey: biology, topography, or melting glaciers?

Persistent organic pollutants (POPs) can be transported long distances and deposited into alpine environments via cold trapping and snow scavenging processes. Here we examined biotic and abiotic factors determining contaminant variability of wildlife in alpine ecosystems. We measured POPs in eggs and plasma of an apex predator, the osprey (Pandion haliaetus) breeding in 15 mountainous watersheds across a broad latitudinal, longitudinal and altitudinal range in western Canada. After accounting for proximate biotic factors such as trophic level (δ(15)N) and carbon source (δ(13)C), variability in contaminant concentrations, including ΣDDT (sum of trichlorodiphenylethane-related compounds), toxaphene, hexachlorobenzene (HCB), total chlordane, and ΣPCBs (polychlorinated biphenyls) in osprey tissues was explained by interactions among relative size of watersheds, water bodies, elevation, and glacial input. ΣDDT in nestling plasma, for example, decreased with lake elevation, probably as a result of local past inputs from agricultural or public health usage at lower altitude sites. In contrast, toxaphene, never used as an insecticide in western Canada, increased with elevation and year-round snow and ice cover in both plasma and eggs, indicating long-range atmospheric sources as dominant for toxaphene. Lower chlorinated PCBs in plasma tended to decrease with elevation and ice cover consistent with published data and model outcomes. Temporal trends of POPs in osprey eggs are coincident with some modeled predictions of release from melting glaciers due to climate change. Currently we suggest that contaminants largely are released through annual snowpack melt and deposited in large lower elevation lakes, or some smaller lakes with poor drainage. Our study highlights the importance of understanding how biological processes integrate physical when studying the environmental chemistry of wildlife.

Rejection of parasitic eggs in passerine hosts: Size matters more for a non-ejecter

ABSTRACT The evolution of egg mimicry by parasites and the recognition of foreign eggs by hosts are important components of the coevolutionary arms race between brood parasites and their hosts, which is one of the most behaviorally complex of all host–parasite interactions. To examine cues used by the Yellow Warbler (Setophaga petechia), a non-ejecter that buries or deserts eggs laid by parasitic Brown-headed Cowbirds (Molothrus ater), we added model eggs of different sizes and colors to nests. We also reviewed the literature to investigate the effects of model egg surface color (background and maculation) and size on the response of hosts that eject. We predicted that size would be more important for Yellow Warblers as they likely use tactile cues to bury or desert parasitized clutches and color cannot be assessed tactilely. In Yellow Warblers, rejection frequency increased as size and color diverged more from real warbler eggs. Egg size was not generally used as a criterion for egg rejection, however, across different species that eject parasitic eggs. Color was the only model egg parameter, out of color and size, that significantly affected rejection in these ejecter hosts. Tactile cues are therefore not used by ejecters but are more important in a host that uses methods of rejection that do not require egg discrimination, such as burial and desertion. Of metrics that took into account the ultraviolet range, achromatic Just Noticeable Differences (brightness) in Yellow Warblers better predicted rejection of model eggs based on color than chromatic Just Noticeable Differences (hue). The high costs of burial and desertion may have led to multiple (size and color) egg discrimination abilities in the Yellow Warbler.

Sex and seasonal differences in hippocampal volume and neurogenesis in brood-parasitic brown-headed cowbirds (Molothrus ater).

Brown‐headed cowbirds (Molothrus ater) are one of few species in which females show more complex space use than males. Female cowbirds search for, revisit, and parasitize host nests and, in a previous study, outperformed males on an open field spatial search task. Previous research reported a female‐biased sex difference in the volume of the hippocampus, a region of the brain involved in spatial memory. Neurons produced by adult neurogenesis may be involved in the formation of new memories and replace older neurons that could cause interference in memory. We tested for sex and seasonal differences in hippocampal volume and neurogenesis of brood‐parasitic brown‐headed cowbirds and the closely related non‐brood‐parasitic red‐winged blackbird (Agelaius phoeniceus) to determine whether there were differences in the hippocampus that reflected space use in the wild. Females had a larger hippocampus than males in both species, but hippocampal neurogenesis, measured by doublecortin immunoreactivity (DCX+), was greater in female than in male cowbirds in the absence of any sex difference in blackbirds, supporting the hypothesis of hippocampal specialization in female cowbirds. Cowbirds of both sexes had a larger hippocampus with greater hippocampal DCX+ than blackbirds. Hippocampus volume remained stable between breeding conditions, but DCX+ was greater post‐breeding, indicating that old memories may be lost through hippocampal reorganization following breeding. Our results support, in part, the hypothesis that the hippocampus of cowbirds is specialized for brood parasitism.

Sex Differences in Spatial Memory in Brown- Headed Cowbirds: Males Outperform Females on a Touchscreen Task

Spatial cognition in females and males can differ in species in which there are sex-specific patterns in the use of space. Brown-headed cowbirds are brood parasites that show a reversal of sex-typical space use often seen in mammals. Female cowbirds, search for, revisit and parasitize hosts nests, have a larger hippocampus than males and have better memory than males for a rewarded location in an open spatial environment. In the current study, we tested female and male cowbirds in breeding and non-breeding conditions on a touchscreen delayed-match-to-sample task using both spatial and colour stimuli. Our goal was to determine whether sex differences in spatial memory in cowbirds generalizes to all spatial tasks or is task-dependant. Both sexes performed better on the spatial than on the colour touchscreen task. On the spatial task, breeding males outperformed breeding females. On the colour task, females and males did not differ, but females performed better in breeding condition than in non-breeding condition. Although female cowbirds were observed to outperform males on a previous larger-scale spatial task, males performed better than females on a task testing spatial memory in the cowbirds’ immediate visual field. Spatial abilities in cowbirds can favour males or females depending on the type of spatial task, as has been observed in mammals, including humans.