Registered Pesticides and Citrus Terpenes as Blackbird Repellents for Rice

Abstract: Nonlethal management alternatives are needed to minimize bird depredation of agricultural crops. We conducted 8 caged feeding tests and 2 field studies to evaluate 2 registered fungicides (GWN-4770, Gowan Company, Yuma, AZ; Quadris®, Syngenta Crop Protection, Greensboro, NC), a neem oil insecticide (Aza-Direct®, Gowan Company), and a novel terpene formulation (Gander Gone, Natural Earth Products, Winter Springs, FL) as avian repellents. For all candidate repellents, red-winged blackbirds (Agelaius phoeniceus) discriminated between untreated and treated rice during preference-testing in captivity. We observed a positive concentration-response relationship among birds offered rice treated with 2,500 ppm, 5,000 ppm, 7,500 ppm, 11,000 ppm, or 22,000 ppm GWN-4770. Relative to pretreatment, blackbirds consumed 34% and 77% less rice treated with 11,000 ppm and 22,000 ppm GWN-4770, respectively, during the concentration-response test. Maximum repellency among other tested compounds was <40% during the concentration-response test. Blackbirds consumed 28% of rice seeds treated with 20,000 ppm GWN-4770 and 68% of untreated seeds broadcast within rice fields in southwestern Louisiana, USA. We observed 50% fewer unprotected seedlings than those treated with 10,000 ppm GWN-4770 within a drill-seeded rice field in southeastern Missouri, USA. The manufacturer subsequently applied for a United States patent for the active ingredient of GWN-4770 as an avian repellent. Although additional registration criteria and formulation optimization must be satisfied to enable the commercial availability of GWN-4770 as an avian repellent, additional efficacy studies of GWN-4770 and other promising repellents under extended field conditions are warranted for protection of newly planted and ripening rice.     

Egg color as an adaptation for thermoregulation

ABSTRACT.   Avian embryos are incubated at temperatures only 2–6 °C below that at which hyperthermia begins to influence survival. In habitats where sunlight directly strikes the eggs, even for short periods, heat gain may be a substantial threat to survival, and reflective pigmentation may reduce the rate of heat gain. The results of previous studies suggest that light-colored eggs acquire heat slower than dark eggs, but artificial pigments were used to create differences in egg coloration. This approach is problematic because natural eggshell pigments have low absorbance in the near-infrared waveband that encompasses about half of incident solar radiation. We used naturally-pigmented eggs to measure the influence of egg coloration on heat gain. Triads ( N = 18) of eggs from Brewer's ( Euphagous cyanocephalus ), Red-winged ( Agelaius phoeniceus ), and Yellow-headed ( Xanthocephalus xanthocephalus ) blackbirds were crossed with six nests of each species and either exposed to full sunlight or placed under a diffusing umbrella. Thermisters recorded internal egg temperature every minute until an asymptotic temperature was reached. Eggs in full sunlight acquired heat more rapidly than eggs in the shaded environment, but heat gain did not vary with egg color in either environment. Eggs placed in Yellow-headed Blackbird nests took longer to reach asymptotic temperature, but there was no significant egg-by-nest interaction. Thus, it appears that differences in reflectivity of eggshell pigments in the visible range (400–700 nm) do not result in different rates of heat acquisition. The thermoregulation hypothesis was not supported.     

Laboratory Efficacy of Chemical Repellents for Reducing Blackbird Damage in Rice and Sunflower Crops

Abstract: Nonlethal alternatives are needed to manage blackbird (Icterids) damage to rice and sunflower production in the United States. We evaluated 4 registered fungicides on rice seeds (i.e., Allegiance® FL, Thiram 42-S, Trilex®, and Vitavax® 200 preplant seed treatments) and 2 foliar pesticides on sunflower seeds (Cobalt™ insecticide and Flock Buster bird repellent) as candidate blackbird repellents. Red-winged blackbirds (Agelaius phoeniceus) preferred untreated rice relative to rice treated with Thiram (P < 0.001) and Vitavax (P < 0.001), and untreated sunflower relative to sunflower treated with Cobalt (P < 0.001). Blackbirds preferred untreated sunflower relative to sunflower treated with Flock Buster repellent on day 1 of a 4-day preference test (P < 0.001). We observed no difference in consumption of treated versus untreated rice during the Allegiance preference test (P = 0.928), and blackbirds preferred rice treated with Trilex relative to untreated rice (P = 0.003). Although repellency was positively related to tested concentrations of Thiram (P = 0.010), Trilex (P = 0.026), and Vitavax (P < 0.001), maximum repellency was < 50% during our concentration-response tests of these seed treatments. Repellency was also positively related to tested concentrations of Cobalt (P < 0.001), and we observed >80% repellency of sunflower treated with Cobalt at ≥50% of the label rate. We observed no concentration-response relationship for the Allegiance seed treatment (P = 0.341) and Flock Buster repellent (P = 0.952). We recommend implementation of supplemental field studies to compare laboratory efficacy, repellency, and chemical residues of effective avian repellents throughout periods of needed crop protection.     

Effectiveness of AV-1011® to reduce damage to drill-planted rice from blackbirds

We determined efficacy of AV-1011® (a 50% anthraquinone product; Arkion® Life Sciences, New Castle, Delaware) on drill-planted rice seed to reduce blackbird damage and determine residue levels of anthraquinone (AQ) in rice seeds and seedlings and in the mature rice crop under field enclosures at the University of Missouri-Delta Center farm near Portageville, Missouri. Red-winged blackbird (Agelaius phoeniceus) damage was higher for untreated than AV-1011® treated rice seedlings at assessment period 3, 15 days postplanting (F_1,141 = 15.81, P < 0.001), and at assessment period 4, 19 days postplanting (F_1,136 = 11.54, P = 0.001). Blackbird damage to AV-1011-treated seedling for assessment periods 3 and 4 was 8% and 7%, respectively, while blackbird damage to untreated seedlings during the same assessment periods was 52% and 44%. More blackbirds used untreated plots than AV-1011-treated plots during assessment periods 2–4 (F_1,17.8 = 20.02, P < 0.001). Overall concentrations of AQ on seeds averaged 5,993 µg/g or 0.59% during the test period. Concentrations of AQ in mature rice seed and plant collected at harvest averaged 1.22 µg/g and 0.10 µg/g, respectively. AV-1011 offers promise for reducing bird depredations to newly planted rice, but additional testing should be conducted to evaluate this repellent in a large-scale field setting. © 2011 The Wildlife Society.     

BODY SIZE AND HAREM SIZE IN MALE RED-WINGED BLACKBIRDS: MANIPULATING SELECTION WITH SEX-SPECIFIC FEEDERS

We experimentally manipulated the strength of selection in the field on red-winged blackbirds (Agelaius phoeniceus) to test hypotheses about contrasting selective forces that favor either large or small males in sexually size dimorphic birds. Selander (1972) argued that sexual selection favors larger males, while survival selection eventually stabilizes male size because larger males do not survive as well as smaller males during harsh winters. Searcy (1979a) proposed instead that sexual selection may be self limiting: male size might be stabilized not by overwinter mortality, but by breeding-season sexual selection that favors smaller males. Under conditions of energetic stress, smaller males should be able to display more and thus achieve higher reproductive success. Using feeders that provisioned males or females but not both, we produced conditions that mimicked the extremes of natural conditions. We found experimental support for the hypothesis that when food is abundant, sexual selection favors larger males. But even under conditions of severe energetic stress, smaller males did not gain larger harems, as the self-limiting hypothesis predicted. Larger males were more energetically stressed than smaller males, but in ways that affected their future reproductive output rather than their current reproductive performance. Stressed males that returned had smaller wings and tails than those that did not return; among returning stressed males, relative harem sizes were inversely related to wing and tail length. Thus, male body size may be stabilized not by survival costs during the non-breeding season, nor by energetic costs during the breeding season, but by costs of future reproduction that larger males pay for their increased breeding-season effort.     

Early arrival, initiation of nesting, and social status: an experimental study of breeding female red-winged blackbirds

Red-winged blackbirds (Agelaius phoeniceus) arrive at breedingsites several months before nests are constructed. Males inthis highly polygynous species presumably return early to defenddesirable territories. Females, however, also begin to arrivealmost two months before nesting is attempted. Early returnto breeding sites could enhance reproductive success by increasinga female's social status and thereby allowing earlier nesting.I measured the effect of experimentally delayed arrival on thetiming of nesting, reproductive success, and social status offemales. Birds were captured as they arrived in early springand detained in an aviary. These experimental females were laterreleased at their capture sites before control females beganconstruction of nests; controls had arrived during the sameperiod as experimentals but were not detained. Experimentalfemales nested, on average, more than a week later than controls,although I could detect no effect of timing on reproductivesuccess during this study. By manipulating arrival date, butnot covariates of arrival time such as age or experience, thisresult indicates that timing of arrival directly influencedlaying date. Delayed females were subordinate to control femaleswith the same mate. This decline in social status may have beenresponsible for the delay in nesting and could have fitnessconsequences for females in some years, because the offspringof earlier nesting, dominant birds are more likely to receivemale parental care in this population.     

An observational and brood-exchange sudy of paternal provisioning in the red-winged blackbird, Agelaius phoeniceus

Male red-winged blackbirds (Agelaius phoeniceus) provisioned50%(118/235) of available broods over an 8-year period. In mostcases, each male provisioned only the oldest brood on his territory,but in 21 cases, the male fed a younger brood after first feedingan older one. In 10 of these cases the switch to the youngerbrood followed predation of the older brood, but in the remaining11 cases the cause of the switch was unknown. To determine whethermale red-winged blackbirds adjust their provisioning when thedemands of their broods change, we exchanged broods betweenpairs of nests on 10 territories. Before each exchange, eachmale had been feeding nestlings of only one of the two broods.In response to the exchanges, male (and female) red-winged blackbirdsimmediately adjusted their rates of provisioning to the increasedor decreased demands of the broods. In addition, most malesswitched their provisioning within a day after the exchangeso that they fed the same broods as before the exchanges. Ourresults show that male red-winged blackbirds adjust their provisioningwhen the demands of their broods change and suggest that maleshave enough information about other nesting attempts on theirterritories to shift to a more profitable brood when the expectedbenefits of provisioning change. Male red-winged blackbirdsdo not appear to follow an investment strategy based on priorinvestments (i.e., they do not commit the "Concorde fallacy").     

A test of the good-genes-as-heterozygosity hypothesis using red-winged blackbirds

Brown recently proposed that the "good genes" that females pursuewhen choosing mates may be individual heterozygosity becausemore heterozygous mates sire offspring with higher fitness.Further, because heterozygosity might enhance developmentalstability, males with more heterozygosity are recognized bythe reduced fluctuating asymmetry (FA) of their bilaterallypaired traits. We used a point sample of 67 male red-winged blackbirds(Agelaius phoeniceus) to test two predictions of this hypothesis:(1) males with more heterozygosity have higher fitness, and(2) males with more heterozygosity have lower FA. We identified7 polymorphic loci from an initial screening of 16 enzymes;32 individuals were completely homozygous, and 35 individualswere heterozygous at at least 1 locus. Larger and older malesrealized higher mating success in this population, but neither sizenor age was related to heterozygosity. Heterozygous males werenot in better condition than homozygous males, nor were theyless infected by hematozoa, lice, or mites. Among 1-year oldmales, epaulet length did not differ between homozygotes andheterozygotes, but among older males, heterozygotes did havelonger epaulets. Homozygotes and heterozygotes did not differin their mean FA scores for nine individual characters. Althoughthe two groups of males did differ in composite FA, heterozygousmales were less symmetrical. Interestingly, this differencewas attributable to a single allele at the PGM-3 locus. Combinedwith previous results showing that FA was generally unrelatedto male health, viability, parental care, social dominance,or mating success, the present results indicate that Brown's hypothesisdoes not explain mate choice or male quality in this populationof red-winged blackbirds.     

MEASURING THE EFFECTS OF PAIRING SUCCESS,EXTRA-PAIR COPULATIONS AND MATE QUALITY ON THE OPPORTUNITY FOR SEXUAL SELECTION

Sexual selection can act through variation in the number of social mates obtained, variation in mate quality, or variation in success at obtaining extra-pair fertilizations. Because within-pair fertilizations (WPF) and extra-pair fertilizations (EPF) are alternate routes of reproduction, they are additive, rather than multiplicative, components of fitness. We present a method for partitioning total variance in reproductive success (a measure of the opportunity for selection) when fitness components are both additive and multiplicative and use it to partition the variance into components that correspond to each mechanism of sexual selection. Computer simulations show that extra-pair fertilizations can either increase or decrease total variance, depending on the covariance between within-pair and extra-pair success. Simulations also suggest that for socially monogamous species, extra-pair fertilizations have a greater effect than variation in mate quality or pairing status on the opportunity for selection. Application of our model to data gathered for a population of red-winged blackbirds (Agelaius phoeniceus) indicates that most of the variance in male reproductive success was attributable to within-pair sources of variance. Nevertheless, extra-pair copulations increased the opportunity for selection because males varied both in the proportion of their social young that they sired and in the number of extra-pair mates that they obtained. Furthermore, large and positive covariances existed between the number of extra-pair mates a male obtained and both social pairing success and within-pair paternity, indicating that, in this population, males preferred as social mates also were preferred as extra-pair mates.