Month: December 2024

There are many possible reasons for why there were different results from these two studies. First of all, the difference in ages tested in these two studies could have played a role as Norman et al. found there was greater success for 28-29 day old chicks when compared to14-15 day old chicks. Additionally, the use of opaque tiers prevented the chick from seeing the reward on the tier in Norman et al. . It is possible that the inability to see the reward reduced the birds’ motivation to jump to the raised platform. Most importantly, the different rewards used could have also played a role in the different performances observed. Regardless of the reasons for the difference in results, this test poses issues when used as an evaluation of spatial cognition. The aspect of spatial cognition being measured was not specified and, more importantly, this test confounds spatial cognition with physical ability. The task increases in difficulty to reach the reward with each trial. This would explain the decrease in number of birds in both rearing treatments that were able to successfully reach the tier as the difficulty increased. Also, providing perches to pullets increases leg muscle deposition in adult hens , which could explain the different performances among the birds of the two rearing treatments. Gunnarsson et al. defended this test as a valid measure of cognition because there was “no obvious reason to believe that the physical effort required to jump from 40 to 80 cm was substantially different” . Although jumping from the ground to the 40 cm tier may not be more physically taxing than reaching the 80 cm tier from the 40 cm tier, these were not the only heights presented to the birds.

It would be reasonable to presume that reaching the 80 cm tier without the aid of an additional platform would be more difficult than reaching the 40 cm tier. The jump test may be used to evaluate differences in physical ability to reach higher tiers, square pots however this task cannot separate physical ability from spatial cognition . For these reasons, the jump test may not be an ideal test to determine if spatial cognition is impaired by lack of access to vertical space during rearing. This test involves presenting a subject with a variety of baited and unbaited holes arranged in a grid. An animal is placed in the arena and is given free choice to visit any or all of possible holes. However, revisiting a previously baited hole will not be reinforced, as the food reward will have already been consumed. Working memory keeps a small amount of relevant information readily accessible while an animal is completing a task . Spatial working memory can be evaluated by measuring how often the subjects revisit holes where they already consumed the reward or holes which have already found to be unbaited . This is measured by the ratio of rewarded visits to the number of visits to the baited holes . Alternatively, reference memory is a form of long-term memory. Spatial reference memory can be examined using the hole board apparatus by repeating the same array of baited and unbaited holes over the course of multiple trials to determine if the animals’ rate of finding baited holes improves . This is determined using the ratio of the number of visits to baited holes to the number of visits to all holes . This improvement implies the location of the food rewards is being retained in reference memory and is being successful retrieved during trials .

Tahamtani et al. investigated the impacts of rearing environment on navigation and spatial memory in laying hens using a hole board task. Chicks were housed in cages for 4 weeks after which the aviary-reared birds were released into multi-tiered aviaries while the cage-reared birds remained in cages until 16 weeks, when all birds were placed in group-housed furnished cages. The hole board task consisted of nine chalk circles with a blue cup positioned in the center, concealing a food reward of live meal worms. The birds were trained to associate the cups with a food reward and only those that readily explored the test arena and found meal worms were selected. Four phases were used for training and testing: uncued acquisition, cued acquisition, over-training, and reversal phase. Uncued training and testing involved baiting only three of the nine cups in the same configuration for all exposures without any specific cues for guidance. This acts as a baseline for the hens’ ability to learn the location of the baited cups without any specific cues. Cued acquisition followed, where hens were trained and tested on the same configuration, however red boards were placed under the baited cups to serve as an extra cue for the location of the food reward. This presents new information that may improve the birds’ ability to complete the task. For over-training, the cues were removed to reestablish their baseline performance. Finally, for the reversal phase, the hens were trained and tested on an alternate configuration of three baited and six unbaited cups. The reversal phase requires flexibility in reference memory, as the birds must override the previously learned configuration in favor of the new information.

It was found that cage-reared birds took longer to complete the hole board task during the reversal phase than the aviary-reared birds, while the aviary birds had a better score for their working memory during the reversal phase when compared to cage-reared birds. This impairment of working memory during task reversal may be due to the decreased complexity found in caged systems when compared to aviary systems. Multi-tiered aviaries provide a greater amount of variability in terms of social interaction and location of resources than caged systems,potentially aiding in the development of spatial learning and memory. The hole board task is an excellent test for evaluating spatial learning and memory, however this test is not relevant at determining if these birds are more capable of navigating vertical space, since it occurs on a flat surface, or geometric plane , and does not take into account vertical space. It offers insight on differences in the working memory of cagereared and aviary-reared birds, however these results do not suggest that chicks reared with access to vertical space have an enhanced ability to avoid colliding with structures.A radial maze is a cognitive task that is designed to evaluate spatial working memory . It involves multiple walkways, or arms, radiating out from a central chamber. A food reward is located at the end of each arm and the subject is placed in the center. The subject is then allowed to freely choose to enter the arms of the maze until all food rewards have been found. The optimum strategy for finding the food rewards would be to enter each arm only once, as previously visited arms will no longer contain a food reward. In order to efficiently solve the maze, the subject must employ working memory to retain information about which arms have already been visited. The animal does this by noting cues, typically extra-maze cues, to determine which arms they have already entered . Since this maze requires adequate spatial memory, it has been employed as a technique to evaluate spatial cognition in fowl raised in environments of varying complexity. Wichman used a radial maze to investigate spatial ability in 16 week old laying hens raised in three different rearing environments. All rearing treatments had access to perches at 20 and 40 cm of height but the control group had not additional enrichments. The floor enrichment group had the addition of wooden blocks while the hanging enrichment group had hanging discs and bottles at beak height. At 16 weeks of age, once all birds had been regularly perching, square plant pot the birds were tested on an eight arm radial maze. Each arm of the maze was baited at the end with a meal worm and birds were given 20 minutes to freely explore the maze. In order to simulate the practice of moving hens from their rearing house to the laying house, all birds were moved to larger, more complex pens at 18 weeks of age. These new pens included perches at varying heights , which could be reached from the floor or by jumping from one perch to another. It was found that there was a relationship between performance on the radial maze and propensity to perch. Birds that used perches the most during the two hours period after being released into the new, complex pens required fewer visits to the arms of the radial maze in order to find all eight of the meal worms. Wichman suggested that based on these results, there is a relationship between two-dimensional spatial ability required for performance on the radial maze and three-dimensional skills required for perching. However, there were no significant differences between the treatment groups for onset of perching or performance on the radial maze. The author suggested that the low height of the perches might have allowed for easy access to vertical space between all treatments. Therefore, there may not have been enough variation between the perching behavior of the chicks to result in clear differences between treatments.

Whiteside et al. used an eight arm radial maze to investigate the impacts of floor rearing on spatial cognition and survivability of pheasants raised in captivity and released for hunting. Whiteside et al. reared one day old chicks until 7 weeks of age in three different environments: standard commercial rearing with no access to perches; access to natural hazel boughs perches; and access to artificial perches. There were no significant differences between the natural and artificial perch groups, so these conditions were combined for analysis.At 6 weeks of age, 27 chicks were tested on an eight arm radial maze to assess their spatial working memory. At the center of the maze there was a circular starting compartment and at the end of each arm of the maze there was a barrier, which concealed a food reward. Orientation in the maze was possible using extra-maze cues as the walls of the testing room were all different in color. The birds were first habituated to the arena for four days and were tested on the task on the fourth day. To solve the maze correctly, the birds had to enter each arm only once and consume the food reward. If a bird entered an arm where they had already eaten the food reward, it was recorded as an error. Those that made the fewest errors were determined to have better spatial memory than those that made more errors. Birds reared without access to perches made significantly more errors in their first eight choices than birds reared with access to perches. This suggests that access to perches at a young age improved the spatial memory of pheasants, potentially aiding in their survival post release. It is also of interest to note that birds reared with perches roosted at night during the two weeks post-release significantly more than birds reared without perches. These two studies demonstrate that performance on a two-dimensional test of spatial memory may impact future use of vertical space. This could have implications for hens’ ability to recall the location of resources and ability to navigate complex environments as an adult .In the detour paradigm, the most direct route to a goal is blocked; the animal must walk around a barrier to reach the goal . For the initially visible goal detour task, the goal is visible at the starting point but then becomes occluded by opaque walls as the animal begins to move through the apparatus. When the goal is initially visible, spatial working memory as well as route planning must occur in order to hold the location of the goal in memory and make choices about what route should be taken. Success on this task is often interpreted as the animal making a mental representation of the location of the non-visible goal and then using this representation to determine the best route . Due to the use of route planning and the need to hold the location of the goal in working memory in order to successful solve this task, the detour paradigm has been frequently used to evaluate spatial working memory and route planning.

For organic growers, two AIs, spinosad and pyrethrins, are available to target those physiological functions. The “unknown” category, which is mostly sulfur, accounted for a significant portion of treated acreage in organic agriculture. Insecticides that target the midgut, which includes Bacillus thuringiensis and several granulosis viruses, are widely applied in organic fields. Conventional growers rarely use them due to the high cost. In 2015, acreage treated with midgut targeted insecticides was 1% of total treated acreage in conventional agriculture and 24% in organic agriculture. A detailed discussion of insecticide and fungicide use by mode of action in conventional and organic production is in the appendix.Insecticides and fungicides in the two pest management programs have different modes of action and pose different levels of environmental impact. Simply comparing treated acreage or the amount of pesticide products used does not identify the differences in environmental impacts. In this context, the PURE index serves as a consistent measure across farming systems.Figure 1.3 plots PURE indices for conventional and organic fields by year. Index values for air and soil are significantly higher than those for the other environmental dimensions in both farming systems, which means that pesticide use in general has greater impacts on air and soil quality than groundwater, pollinators, and surface water. Risk indices of conventional fields are relatively stable from 1995 to 2015, with no obvious overall changes for air or soil, despite the many changes that have occurred during this 20-year period in regulations and grower portfolios. While PURE indices decreased 16% for surface water, 26% for pollinators, grow bag for blueberry plants and 7% for groundwater over the same time period, these three were much less impacted by pesticides in 1995, the beginning of the study period.

Despite the numerous regulatory actions designed to reduce environmental impacts over this 20-year period, such as the methyl bromide phase-out, large-scale substitution of pyrethroids for organophosphates, and regulations to reduce VOC emissions from non-fumigant products, the overall environmental impacts of conventional pesticide use show only limited reductions when aggregated across all crops. PURE indices for organic fields are similar to conventional fields in that the air and soil have significantly higher index vales than the others. However, the aggregate risk indices in all five dimensions are much lower in organic fields. Compared to conventional agriculture, organic agriculture has dramatically lower PURE indices for surface water , groundwater , air , soil , and pollinators . The reduction for air varies greatly across major California crops. Large reductions in the PURE index for air are observed for table grapes , wine grapes , and processing tomatoes , while others had relatively small ones such as leaf lettuce and almonds . The reduction in the PURE index for soil varies across crops as well, ranging from leaf lettuce to carrots . For surface water, groundwater, and pollinators, the differences between the PURE index in organic and conventional fields are similar across crops. A noticeable spike in PURE indices appeared in 1998 for organic agriculture caused by a single application of copper sulfate with an application rate of 150 lb/acre, which is ten times larger than the average application rate and clearly a data abnormality. The PURE index is a measure of environmental impacts on the per acre basis.One could use the yield difference between conventional and organic agriculture to adjust values in Figure 1.3 and transfer them to a measure of impacts per unit of output. Organic agriculture is found to have 10%-20% lower yields than conventional agriculture . If we use the 15% yield loss as an average to adjust the results for all crops, organic agriculture reduced the PURE index for surface water , groundwater , air , soil , and pollinators .

The impact of organic practices on pesticide use is crop specific. This aggregate result is derived based on current crop mix in California. Each crop is susceptible to a different spectrum of pests, which are managed by a distinct pesticide portfolio as part of a broader pest management program. Comparing PURE indices for individual crops shows the benefit from pesticide use in organic agriculture varies significantly. Based on value, production region, and the acreage share of organic production, four crops are selected to illustrate this point: lettuce, strawberries, wine grapes, and processing tomatoes. Lettuce, strawberries, and wine grapes are the three highest-valued organic crops in California, with organic sales values of $241, $231, and $114 million in 2016 respectively . Production of strawberries and lettuce is concentrated in the Central Coast region. Processing tomatoes are an important crop in the Central Valley. Wine grape production occurs in a number of regions across the state. In 2015, the acreage shares of organic production are 8% , 9% , 4% , and 2% for the selected crops.For my analysis, the unit of observation is a field-year, defined as a field with one or more pesticide applications in a given calendar year. In total, more than 3 million field-year observations are included in the PUR database from 1995 to 2015. Table 1.1 provides field-year summary statistics for key variables by crop. Overall, 3% of them applied only pesticides approved in organic agriculture. For all crops, conventional farms are significantly larger in size and have higher PURE indices. The average farm size in PUR is smaller than the average number in the USDA Census . One potential explanation is that one farm could have fields in different counties and apply for multiple pesticide application permits within in each county, which classifies it as multiple “farms” in the PUR. For all crops, lettuce, strawberries, and processing tomatoes, growers who operate conventional farms have significantly more experience, measured by years they are observed in the PUR. For wine grapes, conventional growers have less experience than organic growers. Ideally, farming experience is measured directly or researchers use age as a proxy. However, the PUR database does not contain any demographic information, which limited my ability to measure experience. The PUR experience is smaller than the farming experience reported in the Census, which has many reasons. . First, the PUR database I use started in 1995. Any farming experience before 1995 is not recorded. The Census is conducted every 5 years. Farms that entered and exited within the 5 year gap are included in the PUR database but not the Census, which reduce the average experience. Conventional strawberries have significantly greater impact on surface water and less impact on groundwater, measured by the PURE indices, comparing to other conventional crops. Organic strawberries, on the other hand, had a higher PURE index for air and a lower PURE index for soil than other organic crops. Pesticides used in conventional production of wine grapes have less impact on pollinators than pesticides used in other conventional crops.To identify the effect of organic agriculture on pesticide uses and associated environmental impacts, I must address the issues of selection bias at both the grower and the field levels. Compared to growers who utilize conventional practices, growers who adopt organic ones may have different underlying characteristics, such as attitudes toward environmental issues, which can also affect their pesticide use decisions directly. If grower characteristics are time-invariant, an unbiased estimation could be achieved by including a grower fixed effect in the regression.

There is also time-variant heterogeneity that is associated with individual growers, due to factors such as farm size and experience, blueberry grow bag that simultaneously influences the adoption of organic production and pesticide use decisions. The identification concern here is that growers with more farming experience or larger farms, including both conventional and organic acreage, are more likely to operate organic fields and use less pesticides . Therefore it is not reasonable to compare environmental impacts of pesticide use for growers without considering these characteristics. For each grower, annual total acreage and experience serve as measures of time-variant heterogeneity. As shown in Table 1.1, there is a significant difference for these two variables between conventional and organic growers. There could be field-level heterogeneity as well, due to pest or disease pressure, that undermines my identification strategy. Fields with less pest or disease pressure need less pesticides and are more likely to be converted into organic production at the same time. Including field fixed effects in the estimation is one approach to address these issues. Organic fields tend to be concentrated spatially to avoid pesticide drift from nearby conventional fields . Spatial relationships are not considered here because the PUR database does not have information on the distance between fields.For all five PURE dimensions, pesticides used in organic agriculture reduced environmental impact. The reduction, captures by the variable Organic, is significant at the 1% level for five environmental dimensions. Relative to the intercept, organic practices reduced environmental impacts for surface water by 86%, for groundwater by 93%, for soil by 60%, for air by 53%, and for pollinators by 76% on a per acre basis holding other variables fixed. The relatively small impact on air is linked to the facts that natural AIs do not have less VOC emissions in general. Regulations regarding high VOC-emitting pesticide AIs also contribute to this result partially because they do no affect two systems evenly. In 2015, the sale and use of 48 pesticide products were restricted due to their VOC emissions, which accounted for 5% of treated acreage in conventional agriculture and 1% of treated acreage in organic agriculture. Although reductions in PURE index values do not translate directly into dollar values or health outcomes, results from Table 1.2 suggest that pesticide use in organic fields substantially reduced environmental impacts. The coefficient for Organic × t represents the change of the difference between two farming systems over time and is positive for all environmental dimensions, which supports the hypothesis that, comparing with conventional agriculture, the environmental impacts associated with pesticide use in organic agriculture have grown over time. Air has the largest coefficient among the five environmental dimensions, which is consistent with previous figures that environmental impacts increased the most for air across all crops. The variable t is the common time trend for all conventional fields and t is negative for surface water and groundwater, which means the environmental impacts from pesticide use decreased in conventional agriculture on those dimensions. The environmental impact on soil and air increased. The combination of variables t and Organic × t shows the time trend for organic fields alone, which is upward sloping for groundwater, soil, air, and pollinators, and downward sloping for surface water. Two variables Acreage and Exp, capture time-invariant grower heterogeneity. Although the variable Organic dominates the overall effect, coefficients for both Acreage and Exp influence the environmental impact associated with crop production. For the same grower-crop combination, a larger farm size is associated with pesticide application pro-grams that pose more negative impacts for all five environmental dimensions. Meanwhile, more experience is correlated with the environmental impacts on soil, air, and pollinators. The PURE indices for surface water and groundwater are positively correlated with experience. This is partially due to the fact that experienced farmers use less organophosphate insecticide per acre, which are more toxic to earthworms and honeybees than alternative AIs.The sub-sample estimation yields similar results . Namely, in conventional agriculture, the environmental impacts on surface water and groundwater associated with pesticide use decreased over time, pesticides used in organic agriculture significantly reduced the environmental impacts measured by the PURE index, the difference between conventional and organic pesticide use decreased.The intercept is smaller than the coefficient of Organic occasionally because the crop and time fixed effects are oftentimes positive and significant and the impacts on those dimensions in organic fields are small. For the sub-sample with fields that have transitioned between production systems, total farm acreage is no longer significantly associated with impacts on groundwater, soil, and pollinators and the environmental impact on surface water is negatively correlated with farm acreage. The main reason for this seemingly dramatic difference, comparing to the full sample estimation, is that there are more wine grape vineyards and fewer almond orchards and alfalfa fields in the sub-sample. Although the organic price premium is limited for wine grapes, the organic farming practices are associated with high quality of grapes, which encourage growers to adopt organic production .